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Musings of an Energy Nerd

Is OSB Airtight?

Builders and researchers in North America and Europe report that air can leak right through oriented strand board

Billowing polyethylene provides evidence that air is leaking through this OSB panel. At a Passivhaus job site in Scranton, Pennsylvania, the homeowner, Declan Mulhall (in the green shirt) and building science consultant Pete Vargo (wearing a cap) observe that the sheet of polyethylene billows outward when the blower door is pressurizing the building.
Image Credit: Images #1, 2, 3, and 4: Richard Pedranti

UPDATED on August 13, 2015

Most builders assume — and GBA has long reported — that oriented strand board (OSB) is a good air barrier. If a builder uses a high quality tape like Siga Wigluv, Zip System tape, or 3M All Weather flashing tape to seal sheathing seams, OSB wall and roof sheathing can act as a building’s primary air barrier. Energy consultant Marc Rosenbaum used the technique at two dormitory buildings at the College of the Atlantic in Maine and several projects on Martha’s Vineyard, and subsequently gave a presentation at a Vermont conference at which he advised builders who wanted low blower-door numbers to tape the seams of their OSB sheathing.

In recent months, however, many building experts have been surprised to read reports that some brands of OSB may not be airtight. The reported leakage isn’t coming from poorly taped OSB seams; instead, the air is allegedly leaking through the OSB panels themselves, even when the seams are flawlessly taped. While this type of air leakage sounds unlikely, evidence is accumulating that the reports must be taken seriously.

Among recent developments:

  • An Irish engineer, Niall Crosson, has reported problems with two OSB-sheathed buildings that were too leaky to meet the Passivhaus airtightness standard.
  • Architect Richard Pedranti and energy consultant Pete Vargo performed job-site testing in 2014 that convinced them that air was leaking through the Weyerhaeuser OSB installed on the walls of a Passivhaus project in Scranton, Pennsylvania.
  • Three Belgian researchers — J. Langmans, R. Klein, and S. Roels — have published the results of laboratory tests showing that some European brands of OSB aren’t very airtight.

Defining acceptable air leakage

What’s the definition of an air barrier? In North America, some building codes have adopted the following definition: an “air barrier material” is defined as a material with…

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  1. wjrobinson | | #1

    Insane to think cheap is not cheap.
    This blog s a mile too long for this farmer taught boy.

    Premise; Let's build an expensive high tech PH. Let's build it with crap. What's wrong, oh the crap is bad? Those lousy manufacturers!!! How can they be so bad! I want top notch cheap not!!

    Cheap cheap! That is my short message instead of a thousand word blog and million dollars of future studies. Give me a break.

    PH folks... here's the lesson to learn. You get what you pay for!

    Buy Zip, even my nearby home being built horribly has Zip!!! It also has 1/2" dow foam going over the Zip. I guess 2" is too much money.

    Money, budgets drive us all to make stupid decisions and choices.

    If I were to build PH I would try the liquid coatings mentioned. and not frame in December! There are two homes going up where I travel daily and both could care less that the Zip tape is peeling off.

    Good luck trying to convince a homeowner that since the permit process had delays we should not start the project now on January 1st! Twice for me they just said push ahead. Nuts. I just signed a job for a civil engineer who easily saw the merit of going with a finish date not a start date of Jan 1. Thank you sir for your sensibilities.

  2. wjrobinson | | #2

    Without the fan.
    How many

    Without the fan.

    How many homes have blower doors in them while they are occupied? NONE.

    My question is... what would have been the added fuel cost or whatever if this home in Scranton had been finished and they gave up on the PH plaque for the wall?

    $3,000 saved right away.
    Toss the PH Pro off the project and end payments.
    A couple weeks of fidgeting and fretting and paying carpenters to do the same. $$$$

    I bet the fuel cost wouldn't go up $10/yr. and

  3. wjrobinson | | #3

    Martin, get a hold of the
    Martin, get a hold of the testing experts and ask them how leaky the crappy OSB is if it is not under 50 pascal pressure more like a normal everyday pressure like the pressure of the stack effect?

  4. wjrobinson | | #4

    Martin this is a serious
    Martin this is a serious request. What pascal number is normal average for a home to be put at over the course of a year averaged?

    A PGH home with 1.2 number like these over the top boys got at the test would be heaven for this farmer taught gent.

  5. wjrobinson | | #5

    4 PA verses 100,000 PA
    natural air pressure difference is 4 PA

    14psi is 100,000 PA

    Can't believe 4/100,000 is something shoving air molecules through crappy OSB.

  6. wjrobinson | | #6

    50 PA is used to obviate the
    50 PA is used to obviate the effects of stack and wind.

    It also must make OSB do something it most likely does not do at 4 PA which is said to be the natural pressure difference.

    Somebody tell me I'm crazy or they are.

  7. GBA Editor
    Martin Holladay | | #7

    Response to AJ Builder
    The questions you are asking are the same questions that I raised in the last three paragraphs of my article.

    I look forward to seeing the results of air leakage testing on North American brands of OSB. At this time, the data do not exist.

    You're correct that it would be interesting to compare leakage rates at 50 Pa to leakage rates a lower pressures -- perhaps 25 Pa, or 10 Pa, or 4 Pa, as you suggest. We need labs and manufacturers to perform the tests so that these questions can be answered.

    In the meantime, anyone who builds a Passivhaus has to meet the 0.6 ach50 requirement. Meeting this target is not optional. For these builders, the performance of OSB at 50 Pa of pressurization and 50 Pa of depressurization is absolutely relevant.

  8. AntonioO | | #8

    I'd look at the glues
    Having done some work on the micro adhesion properties of soft polymers some time ago, I'd take a close look at the glues used to make this material. Even the same generic polymer can have quite different properties depending on how it was processed and its temperature history. It wouldn't surprise me to find that the polymerization of glues used by a particular brand is considered a trade secret though. The next logical thing to think about along these same lines is how well the OSB glue performs after 5 to 10 years of winter/summer cycles--especially in cold climates. I'm guessing manufacturers were more concerned about strength properties than airtight-ness when deciding what to test.

  9. wjrobinson | | #9

    Antonio in the real world this debate is about nothing.
    Say you build a PH, then the glue performs less so in a decade so now your natural ACH is what? It wouldn't change enough to be measurable is what! Change in heating degree days due to solar flares does more to change an annual fuel cost by a $10 bill. Islamic Estate is changing your annual costs way more than your crappy OSB folks.

    Get real. We in the USA live in a glass house. Martin knows much of this with his world travels and my two visits had me in tears upon seeing swimming pools in every back yard flying back into Miami.

    If you want the PH plaque the simple answer is to enhance your sheathing, ZIp comes enhanced and there's liquid applied and all the rest.

    It's not worth improving OSB for air leaks IMO. The aim of OSB production is low cost low cost low cost. That is the main objective given to the engineering group no matter what the marketing folks are saying as they are given the task to make an ugly duck smell like roses or something like that. LOL

  10. mackstann | | #10

    50Pa vs. real world
    Air pressure is air pressure... intuitively (and I know intuition can be wrong), it seems very unlikely that OSB somehow leaks at high pressure but does not leak at normal pressures. Sure, its leakage is low compared by any but Passive House standards, but this is all about PH testing. If you're worried about gaps and cracks, you might as well be worried about leaky OSB too.

    I don't pretend to know enough to not possibly be taking this out of context, but I found an interesting statement in this paper:

    "In addition, extrapolation of results from tests at high pressures to those typically experienced by a building envelope does not introduce a bias in infiltration predictions."

  11. Richard Beyer | | #11

    I'd look at the glues by Antonio Oliver
    "Fiberboard and particleboard lumber are built-up from wood particles bonded together by an adhesive, the adhesive being selected according to the intended use of and the properties desired for the lumber. Often times, the adhesive is combined with other additives to impart additional properties to the lumber. Common additives are fire retardants, insect repellants, moisture resistants, fungus resistants and color dyes. In some fiberboard and particleboard lumber products, wood particles have been combined with other cellulosic materials, such as vegetable fibers, pulp and the like. A significant advantage of fiberboard and particleboard lumber products is that they have many of the properties of plywood, but can be made from lower grade wood species and waste from other wood product production,

    Commercial phenol–formaldehyde (PF), used as oriented strandboard face and core resins..

    (P-MDI) Polymeric and (E-MDI) emulsion type Isocyanate Resins and Acetone (used to even out the resins during manufacture) are also used in High Performance OSB.

  12. dankolbert | | #12

    Is it air-tight?
    As Martin describes, "air barrier" is just a line that got drawn, with thought but still somewhat arbitrarily, not a bright line dividing one side and the other. If a material is good enough to get you to 1.0 but not 0.6, what does that mean? I don't know. Some material is always going to be your weak link no matter how tight you get it.

  13. GBA Editor
    Martin Holladay | | #13

    Response to Nick T
    Q. "Is this air leaking OSB different then the OSB of old?"

    A. There are no data on this issue whatsoever, other than a couple of European studies. So the answer to your question is: we don't know.

    Q. "Is it maybe intentional to increase the drying ability of the boards or walls?"

    A. There is absolutely no evidence of that. Certainly none of the OSB product specialists at any of the manufacturers I contacted suggested that.

    Q. "Isn't perm of sheathing a spec on lumber?"

    A. While many laboratories have tested the vapor permeance of different brands of OSB, I don't think there are any regulations requiring a specific vapor permeance range.

  14. Cjb80 | | #14

    I had posted a question
    I had posted a question about this subject here in the Q&A section about a year ago and the general wisdom at the time was that OSB was air tight (a search could probably find this question). At the time I had done some internet searches and found some forums were builders from outside of NA were finding that their OSB was leaky....

    Anyways, my question is what evidence do we have that plywood is not leaky?

  15. GBA Editor
    Martin Holladay | | #15

    Response to Chris Barnes
    Q. "What evidence do we have that plywood is not leaky?"

    A. The evidence comes from laboratory testing performed by Canadian researchers in 1998. My article includes a link to a report of their findings: Air Permeance of Building Materials.

    The rate of air leakage through 8 mm plywood sheathing was found to be 0.0067 l/s-m2@75 Pa.

    The rate of air leakage through 9.5 mm plywood sheathing was so low it was called "non-measurable."

  16. jinmtvt | | #16

    AJ ur the man lately!
    You seem to be "on fire" as of late!!

    Cheap arse products are used on some PH projects because the "budget" was spent elsewhere.
    No other reasons.

    Plywood is my friend.
    I like it alot.
    It looks like actual wood, not a compressed puzzle of particles.

    Never found numbers,
    but as i stated before, i am quite sure that plywood has more wood and less glue to it
    than OSB, thus it should be greener.

    There are some very cheap painting products that could be used to coat plywoods right before being applied ( like coated in a shop ) that would make them fully water resistant.
    I bet we could find some natural oil ,wax mix or something similar that woudl be green.

    Something i'll try and look out for in the next years,
    before spending hundreds on peel sticks and wraping buildings in bad for health adhesives
    and plastics .

  17. ntisdell | | #17

    Perm of OSB?
    Is this air leaking OSB different then the OSB of old? A push for less glue, due to weight? Glue costs? Or is it just a batch issue - kind of hit or miss - depending on humidity/glue/compression/dryng speed...etc?

    Is it maybe intentional to increase the drying ability of the boards or walls?

    I know that Perm and Air barriers are different - but have to imagine something riddled with holes will also have a higher vapor/moisture transfer ability. Isn't perm of sheathing a spec on lumber?

  18. user-1026988 | | #18

    The Langmans paper dates back to 2010. I have been having this conversation with The Euros' since about '08. The reality is that some OSB products are airtight and some are not. When dealing with PH levels of airtightness it can and does make a huge difference. Having designed, built and tested many homes using OSB as an air barrier ranging in airtightness from .95 (lame) to .18 ACH 50(beyond robust) I can attest to the real world in situ performance of OSB as an airtight later.We have also used fabrics and bituminous membranes as well as fluid applied. I have opinions on all of them. Not all fluid applied membranes are created equal and not all OSB is created equal. To label OSB as crap because of its expense is ridiculous. The cost of an item does not affect its performance.
    When it come's to leaky OSB I am less inclined to look to the glues and more inclined to think of the 'strands' themselves. OSB manufactured in the north is fabricated from hardwood; predominantly Aspen, and in some cases I have heard of poplar,oak and and other hardwoods being thrown into the mix but I have never been able to verify ( or tried to hard for that matter).
    In the south OSB is fabricated predominantly with SYP. Softwood. The same phenomenon occurs in the EU. For what it is worth stepping up to 5/8 and especially 3/4 closes the air tightness gap.
    I have personally tested both Arbec ( Quebec and NB. Canada) and LP ( Holden Maine) OSB's and found them to both be airtight at 75-125 PA. The Langmans' study poses an important result:
    1- not all OSB is equal
    2- OSB ranges from airtight to not airtight
    3- Nobody knows who the hell is what in the study, so none of us are wiser consumers (gotta love European govt. funded social graces)

    Air tightness is a quality thing as well as the best bang for the buck to save energy, but the quality thing to me is much more important. The less the infiltration and exfiltration, the less vapor is traveling through the assembly. The more robust the assembly.

    Thanks to Richard Pedranti for publishing his results with leaky OSB. Not only proving me wrong in a 5 year disagreement with some other plugged in dudes, but also for 'possibly'? edifying the notion that this is an issue of materials (Hardwood v. softwood) in the production process.

    Who knows???????????

  19. jackofalltrades777 | | #19

    Just use ICF
    Simple solution: Just build with ICF (2.5" EPS x 6" concrete x 2.5" EPS) and that is about as airtight as you can get.

  20. jinmtvt | | #20

    2.5" ICF forms are sooooo yesterday!
    You gotta up to 4" +4 " if u wanna get some respect around these parts mate! :p

    I do agree with all of my ICF walls ( my house ) that they tend not to leak much.
    The window bucks area is another problem though and need to be detailed very carefully!

  21. GBA Editor
    Martin Holladay | | #21

    Response to Christian Corson (Comment #18)
    Thanks for your comments. Almost all of your observations are consistent with what I wrote.

    I appreciate the fact that you have added two brands of OSB to the list of "probably OK" brands: Arbec OSB from Quebec or New Brunswick, and LP OSB from Houlton, Maine. Thanks.

    I'd like to point out that one of your statements -- "stepping up to 5/8 and especially 3/4 closes the airtightness gap" -- is an unproven hunch, especially in light of the fact that all of the samples of OSB tested by the Belgian researchers were 3/4 inch thick.

    For what it's worth (if I am reading the OSB grade stamp correctly), the OSB on the house in Scranton, Pennyslvania was 418/1000 inch thick -- a little less than 7/16 inch.

  22. GBA Editor
    Martin Holladay | | #22

    Remember the topic of this article
    A note to readers: the topic of this article is air leakage through OSB. I'm grateful to Christian Corson (and several other posters) who submitted comments that were relevant to the topic.

    A few readers (one of whom admits he hasn't read the article, and another of whom says he doesn't have to read the article) have posted off-topic comments. We've learned that OSB is cheap, for example, or that ICF walls are great, or that in the future we will all be sheathing our homes with carbon fiber panels.

    All comments are welcome -- but I am especially interested in comments on the topic of air leakage through OSB.

  23. RZR | | #23

    I didn't read the article, no need. Out of all the composites I have designed for decades OSB makes the least sense. If you have ever been part of the manufacturing processes the battle is always voids and delaminations. Take a porous material wood throw it in with some phenolic resign and catylist in hopes that is seals the wood without a ultra sound or x-ray test most manufactures do not perform results in any of number of permability to the consumer. The ASTM does not call out a void or delam size nor inspection criteria and corrective action. Having to find the them and fill them with injections is costly, OSB would not be the cheap. There is definitely a relationship between cost and quality.

    One could take some wood chips and lime mixed in a mortar mixer and have a MUCH better product. In this case, the casting over framing would seal as it dried, and breath (voids are good). You run some test like the manufactures to determine a ratio, r-value, perm rating, easy! No siding, insulation, drywall, vapor protection, needed.

    A sheet of phenol resin and catalyst with glass fibers would make more sense. If structural, woven glass fibers, or better graphite, embeded in resin....when this day arrives we will not need framing, siding. "Marine Board" plastic sheet does much better and handles moisture, you get at a local plastic manufacture without the wood chips. It cost a little more, you don't need siding.

    The resin is the moisture and air barrier in this laminated assy, the wood is to cut cost of the resign an create voids that the resign needs to infiltrate and seal.

    OSB-Glue-OSB, SIPS, same issues, junk!

    The best ply's are "pre-pregs" Here a manufacture takes glass or graphite cloth and impregnates it with resign to reduce voids. You stack up plies to a desired thickness, the only voids are between plies if the manufacture does not get the temperature and pressure correct. If they don't then we get dry areas or resign starved. In that case, a disposition to fill the area, costly. The edge in another area of bleed out from the pressure plates used to put the assembly under pressure.

    It won't be long as cost drops carbon fiber reinforced plastic (CFRP) sheeting pre-preg replaces junk OSB and is SIPS.

    Lots of varaibles manufactures can screw up including Huberd and GP the big fish.

    Taping seams won't last, not room temp cure adhesives with low lap tensile-shear of less than 100 psi, after so many thermal cycles they will leak. I have validated this time and time again. Take a blower door after 5-10-15 years see for yourself. If you are going to do this DO NOT design it, use a ZIP systems where Engineers have tested the type and content of phenol-cat ratio's that mate to their tapes adhesive type and properties. You could always ask for lap tensile and shear of any tape against the specific OSB you are attempting to design, and ask the tape manufacture for fatigue life testing against the OSB you are using. I doubt you find that, it is an unknown you chance. Noone should advise others to use something there is no data for or they do not understand completely!

    ZIP is an improvement since if I remember right they came back with a co-cured glass ply in a second stage bond operation to add a WRB and seal any voids, however there is always the possibility of a delamination.

  24. RZR | | #24

    Air leakage through OSB
    Marin, read my post again. I discussed it in great detail. I don't need to read the article since I have 30 years experience manufacturing composites at companies like Georgia Pacific GP and Huber and larger. Last I checked direct experience speaks volumes.

    If anyone has any question as to why exactly they leak you will find that in my last post along with tape properties that cause leakage. If you have never worked for the manufacture or have direct experience producing OSB you probably won't get it.

    Also, feel free to call the engineers at Hurber and GP to validate the accuracy of my post, I have discussed this with them many times.

  25. STEPHEN SHEEHY | | #25

    My contractor and I discussed using cdx sheathing, but his recent experience here in Maine is that cdx available locally more often than not is badly warped, has too many voids, etc. We opted for Advantech instead. Joints are taped with 3M 8067 tape. The tape sticks really well to cold, damp surfaces.

  26. user-1026988 | | #26

    Thanks Martin
    Your comment : I'd like to point out that one of your statements -- "stepping up to 5/8 and especially 3/4 closes the airtightness gap" -- is an unproven hunch, especially in light of the fact that all of the samples of OSB tested by the Belgian researchers were 3/4 inch thick. - You are absolutely right, and I apologize for the context getting lost in brevity

    This comment was made in regards to conversations about the potential for leaky OSB in the US market and whether a thicker specimen would make a difference. 7/16 being the standard thickness used in in the US as sheathing.Again I reiterate that my thought is that the difference is in the material fibers. The reality is that the thickness is mute point. If one were to step up to 3/4 in OSB per say than the cost delta to zip sheathing would make that particular product a more attractive option.

    As far as I know RP's experience is the first documented case of leaky OSB that I know of in the US. This deficiency is well known in Europe and one reason why dedicated control layers are intrinsic to resiliency in buildings.

    OSB was designed as a racking layer, It is sheathing. Not as an air barrier. The structural integrity of OSB is certified by TECO and the APA so to blatantly call it "crap" borders on trolling.

    Martin, thanks for a great article and bringing this discussion forward. It is disheartening the see the quality of these articles sullied by some on the comments.

    Huber ZIP and LP OSB are manufactured in Houlton NOT Holden Me. Typo on my part.

  27. RZR | | #27

    Thickness is not the issue, do not be fooled into thinking that there is a direct relationship to it and air-tightness, more is better. More thickness, more material, more temp, more pressure, more potential for voids. It is not a problem to design and produce air tightness in any thickness if the quality and manufacturing process is right.

    Since the so called topic is "air tightness" I won't get into too far into "structural integrity" since I'm the one Martin will call out on going "off topic", hummm! ;) but let me tell you, OSB does not provide THAT much 'racking" resistance, or a better definition is resistance to rotational moments, or 2nd moments of inertia. Actually, OSB differs in it's ability to take out loads unilaterally since the strands and grains are multi-directional....this is nothing new, laying down multi-directional plys or, adding wood or glass fibers to resign systems has been around for decades and is the basis for the design. Plywood has better directional properties along the grain direction and is not as unidirectional, it is stronger, however, at resisting racking or bending, and/or shear plane loads at the multiple bond lines. The bond lines, depending on voids, are the structure and gives it "integrety" or strength. If there are voids or delams the structural properties and knocked down. Most failures occur or should occur at the bond lines. There are better choices than both.

    I advise manufactures to use a oil additive to help with resign flow and saturation of the wood chips along with pre-preg soaking. Air tightness has is very dependent on bonding temps and pressures, FOD (foreign objects damage) along with the ratio of resign-to-catalyst-to-oil that can vary drastically between manufactures, not thickness. I believe advantec due to the glass second stage bond is air and vapor impermeable, and very strong......structurally it combines the best of both worlds, multi- and uni-directional strength.....again not new, that came from laying down fiberglass plies at different orientations (0, 45, 90, 180, 270) degrees and either room temp of elevated temp and pressure cures)....

    Tapes will never see the mechanical and thermal air sealing or strength at room temp cures that high temp and pressure bonds have. As I said, it is a system stick with the same manufacture or look at properties if you are a designer.

  28. Kopper37 | | #28

    Engineered Sheet Good

    I worked in a high-end cabinet shop for a couple of years. During that time we upgraded our CNC equipment. With the older model we secured the machining substrate (MDF) and the hardwood parts with fasteners. We fastened the MDF to the CNC frame with screws, countersunk from the top; we then screwed the hardwood parts to the MDF with screws, from the back. It was a cumbersome process.

    The newer model used a vacuum manifold to hold the MDF substrate in place. To our amazement, the vacuum also held the hardwood parts in place--through the 3/4" MDF substrate! As the manufacturer described the phenomenon, the MDF was extremely porous. The tiny gaps between the wood particles acted as a filter, but did not significantly inhibit the level of vaccum achieved at the MDF surface.

    I'm sure there are significant differences between MDF and OSB (and the rate of depressurization between a CNC vacuum and a blower door test). However, there are a lot of similarities. Both are engineered sheet goods. They are both manufactured with wood strands or wood flours, resins, heat, and pressure. They are both porous products--look at these products closely and you will see the gaps between the particles. And they are both produced in various densities.

    I recenty had a lengthy discussion with a Huber sales representative. He clearly described the differences between their product line-up (AdvanTech flooring, AdvanTech sheathing, and ZIP sheathing) and other OSB manufacturers. He stated that the strand size, strand orientation, resin type, resin content, and overall board density all affected product performance. He emphasized that they used a more costly and difficult-to-use resin to manufacturer their boards: MDI, methylene diphenyl di-isocyanate. He said that the resin was very important in determining their OSB quality.

    Interestingly, their AdvanTech products are tested and rated according to ESR-1785, which qualifies their product as having greater stiffness and nail holding power. Handling a sheet will reveal the density difference between various OSB products. And their ZIP sheathing is tested according to ASTM E 2178 (<0.02 L/s.m2). I believe they are the only OSB manufacturer that has actually tested and rated their product as an air barrier. Whether this product parameter is a result of the sheathing overlay or the actual OSB board . . .who knows?

    This is not a plug for Huber. We are using GP's Plytanium plywood for our sheathing layer and air barrier. Plywood has its own faults, which are well documented, but we still lean in that direction.

    As a final thought, perhaps a call to Huber's technical department might shed some light on Chris Corson's theory about hardwood vs. softwood strands. They have a plant in Easton, ME, but most of their manufacturing takes place in the south (presumably with SYP strands). Personally I think the gaps between strands--and how they communicate with each other--are more important. In any case, they are probably best positioned to address the issue of OSB leakage since they have studied the issue enough to figure out what it takes to make a board capable of meeting the ASTM standard.

  29. GBA Editor
    Martin Holladay | | #29

    Response to Daniel Ernst
    Thanks very much for your useful comments. The anecdote about the air permeance of MDF is quite interesting.

    Advantech seems to be an excellent air barrier; if you look closely at the photos of the OSB on the College of the Atlantic in Maine -- the project where Marc Rosenbaum first used taped OSB sheathing as an air barrier -- you can see that Advantech was used on that project. That probably accounts for the project's success.

    I've never heard of any air barrier problems attributable to Huber products (Advantech or Zip).

  30. user-1026988 | | #30

    For non specific lateral forces on frame, OSB gets the job done. If you want to use CF more power to you. I appreciate your comments, and to the greater extent agree with most of them, but we are talking about building building's here. When GBA changes its name to Green Aerospace Advisor everything you just said will become much more relevant.
    Just Sayin. ( I dont use emoticons but if I did, I would insert a winky,smiley here.)

  31. RZR | | #31

    I'm laughing! I do tend to over think, can't help my background. I sit back and look at the titles now, no need to read what I have been a part of solving for the past decades.

    "Green Aerospace Advisory", did you know they are green when they come off the line prior to paint? I was thinking more along the line, Green Foam Advisors....since it is the solution to most problems out here ;)

    OSB-FOAM-OSB ....Now we talking GBA talk ;) SIP it up, or ZIP it up, your call ;)

  32. user-1026988 | | #32

    Thanks for appreciating my sense of humor. For what it is worth, I am a cellulose guy. I know, I know, I could use aerogel, but then what we would have to talk about ?

  33. user-1081937 | | #33

    Killing two birds
    This is such a great conversation as using your sheathing layer as an air barrier is one of the few places we can kill two birds with one stone in our wall assemblies. I can only add some anecdotal information. We have had two houses sheathed and taped with OSB (LP 15/32 I believe) and one came in at .35 ACH 50p and the other .25 ACH 50p, and one house using CDX which came in at .45 ACH 50p.

    At these levels of airtightness its not possible to isolate a single product but bodes well in my book for taping a stock sheathing material. In Europe they have 4 grades of OSB, and this issue came up in conversation I had with Dr. Benjamin Kirck at PHI in Darmstadt. They have definitely seen a big difference in the air permeability between the grades. Since we are not using graded OSB it is more about learning from experienced folks what is working and what is not. Resorting to a ZIP wall, or heaven forbid ICF seems like a big leap in cost that may not be necessary. It also shows how important doing an air pressure test at sheathing stage is. I think that if there is doubt then use a four ply CDX and hope the knots don't line up!

  34. RZR | | #34

    ZIP and Engineering
    ZIP has not passed the test of time yet, we don't know what it's life cycle cost is. We do not see life cycle test on the data sheets. The tape will more than likley be the first failure in time, when depends on the temperature and pressure cycles. It's not if, it's when. Concrete in much stronger, especially in winds greater than 90 mph, or better hail, 150-250 mph, and large temp swings, acids, salts, rot, decay, fungi.

    Call an engineering dept have fun, lol! You'll more than likely get a college kid since the seniors are doing real work besides answering every joe blows questions. Ask a "sales rep" oh my, I'll leave that one alone....The new term is "sales engineeeeer' same ol, same ol, business degrees all they know is what they think they heard some Engineer say in a staff meeting or a manager that has no idea. Take ten different senior engineers, do not be surprised if you get ten different answers.....your best bet is to be an Engineer that knows what questions to ask and can tell how knowledgeable the person is you are talking to. Or better yet look at test data or lack of it (unknowns) on the site.

    A blower door test is a snap shot in time usually taken during or after new construction, not to be confused with life cycle. If you need several, you may want to look for a better lower cost solution that is clearer and reliable over long periods of time.

  35. RZR | | #35

    Vacuum Pressure
    ' I love big tools, but my sense is that there is a big a%# compressor lurking behind that CNC hold down table, and I like it. '

    Christian, it's not a compressor, it is a vacuum pump that pulls around an 1-3 inches of mercury to suck down plys. OSB is pressurized by caul plates, or pneumatic, hydraulic, mandrels. Autoclave cure temps around 200-350 F.

    Porous materials under sealed vacuum pressure have no effect on the required pressure, that is a well known fact anyone that has done this before would know.

    You have made some bad statements in your post that Martin seems to value because he obviously has no experience with it, I know are wrong. I'd pull out more but no need, I know.

    BTW: Most industries follow and market aircraft level technology which in most cases in sales hype BS! This industry is far behind it, but will take on alot of it's technology as it already has, I pointed out, to include graphite composites...stupid not to when the properties far exceed wood, concrete, e-s glass, hybrids.

  36. Kopper37 | | #36

    This is a porous conversation ;-)

    It sounds like you have studied the issue at great depth. The decision to use one sheathing over another is largely dictated by cost. Most of the industry uses commodity OSB because it has the lowest price point. Regardless of the manufacturer, if it has the stamp, then it meets the APA standards for sheathing. Like you said, they're not making it or advertising it as an air barrier.

    Builders of high-performance, energy-efficient, or "green" houses evaluate the products on very different levels. That's a small, but growing percentage.

    FWIW - Currently I can purchase a high quality CDX plywood for less than ZIP sheathing. Whatever helps you sleep at night, huh?

    It's funny that you mentioned the vapor permeance of the ZIP product. The Huber rep. quoted that figure to me also; I was quick to challenge the number. He clarified by stating that the overlay had a rating of 12-16 perms, not the sheet.

    Huber also likes to demonstrate the low wicking potential of the AdvanTech product (you've probably seen AdvanTech vs. plywood soaking in the red dye). I told the rep. that one of the reasons I choose plywood is the very fact that it does wick so well. He looked at me like I was crazy.

    There are several OOMs difference between the pressure of a CNC vacuum and a blower door (and yes, that big a%# pump is quite awesome!). That said, I guess I was trying to make the point that this is not a question of if, but how much. All of these engineered sheet goods are porous and air permeable. Whether or not a particular brand of OSB is porous enough to negatively affect a blower door result . . . that's the million dollar question. It sounds like most PH builders are winning that lottery--and unfortunate that Pedranti lost.

    Perhaps the attention that Martin is bringing to the conversation will lead to improved industry standards. Me, I'm still waiting for a company to start producing a plywood version of Huber's ZIP sheathing . . .

  37. Kopper37 | | #37

    "Duclos method of airtightness?"
    From the pictures it appears that Pedranti sheathed the entire structure before conducting the first blower door test (what Adam Cohen calls the "Duclos method"). Do you know if this was the case?

  38. gusfhb | | #38

    What makes me
    What makes me think.............

    If there is that much variance in airtightness, what is the variance in strength?

    I mean, air barrier is a secondary consideration, OSB is supposed to be a structural material, if the manufacturing varies that much......

  39. jackofalltrades777 | | #39


    You are being unnecessarily harsh on SIPs. The SIPs that were made back in the 1970's are still standing and still doing OK. They were OSB-EPS-OSB. Millions of homes are sheathed with OSB and they are still standing.

    I think people are making a mountain out of a molehill on this OSB issue.

  40. RZR | | #40

    Peter L, I agree SIPs has some great benefits I will expand on in great detail after I see the answers to some of the questions above, can't wait for Martin and perhaps AJ builder follower to spread some light here.....oh my, LMAO! :) I'm too afraid to go, well, you know, "off topic" although AJ builder does on just about ever thread I see him on which is most, go figure! :)

    Love it! :)

  41. GBA Editor
    Martin Holladay | | #41

    Response to Terry Lee
    While your comments frequently note that your knowledge exceeds that of everyone else who writes for GBA, and that most building materials are much worse than the materials used to build aircraft, I'm sorry to say that these observations aren't very relevant to the day-to-day problems faced by residential builders.

    It is perfectly possible to build a house with poured concrete walls and a carbon-fiber roof -- as well as a $50,000 engineering budget --- and you are free to do so. Such a house is likely to last a very long time. That said, many builders need to advise their clients on whether to sheathe their walls with OSB, plywood, or Zip sheathing. This article attempts to provide information that will help such builders understand the issues behind that choice.

  42. GBA Editor
    Martin Holladay | | #42

    Response to Daniel Ernst
    Yes, Pedranti was following the Duclos method. In his e-mail to me about his approach to air sealing and blower-door testing, he noted that he was following the three-test Duclos method.

  43. wjrobinson | | #43

    PH builders
    PH builders, I would think all of you would purchase your own blower doors and learn how to use them. Do you all do this? And now that it seems you need to use the lowest cost sheathing as a true air barrier then next on the list would be to build a simple sheathing tester. Build your box, and test a sheet from your supplier.

    You build expensive high tech homes. To test your sheathing seems like the simple next step.

    My earlier posts referred to OSB as cheap, where I come from any time the lowest cost item is preferred or purchased we call that the cheapest and call each other cheapskates. For example, go buy the lowest cost cell phone or a high cost cell phone. I bet most of you do not buy the lowest cost cell phone if you are a PH home builder. I make sense to me, you do not make sense to me, but there is room on the planet for both of us.

    Buy the lowest cost anything and good for you, you saved. You get what you pay for most of the time folks.

    Do some extra work, build a test box on a Saturday and you can rest easy that the low cost OSB you need is going to do the job. You don't need the industry to do a million dollar study, do a $100 dollar project for fun too in half a day. Even Terry Lee could do this for $100 and no team of Boeing engineers.

    [Inappropriate comments deleted by GBA editor.]

    Martin, why do we capitalize days of the week? Are they that important? sunday Sunday... sunday is fine for me... like aj... what am I a king? King Aj? Terry Lee, what do you think? terry lee or King Terry Lee?

  44. albertrooks | | #44

    Very surprising issue
    Hi all,

    To date I had only heard rumors of this issue. It's interesting to read about a well documented occurrence. For my part, this does not seem to have come up in the West, or at least the Pacific Northwest. It's true that many builders have moved to Huber Zip, but that aside, there have been many projects since 2010 that performed well below 0.60 ACH 50 using OSB (Including Dan Whitmores 1st project).

    Artisan group has reported that the last 2 project results at 0.06 & 0.075 ACH 50. This is a factor of 10x past the PH requirement. The typical build is with OSB. I'll check to see if that is still the case.

    People occasionally express concern about plywood since when taping it you can miss lateral voids at the top veneer layer. One way to deal with this is (if you like to tape) is to roll on a primer. It will fill any lateral void, nail tear out etc... Another good solution is to use Prosoco Joint and Seam Fill (Note that J&S should always be top-coated with Fast Flash in exterior flashing applications).

    I like Chris Corsons Hardwood/Softwood theory. Out here in the west we are mostly softwood in OSB. However an additional improvement to lowering the air permeance of a composite is to add "fillers" into the adhesive. While softwoods may compress more readily and "fill gaps", it's not hard to add a "filler" to the adhesive at the production line. The filler would also help keep water out of the "stands" making up the OSB by closing some gaps for moisture to travel. While I don't know this to be the case, it does make sense in a "soggy" climate.

  45. user-741168 | | #45

    only slightly off topic
    Well, we don’t know as much as we’d like to about OSB. Which reminds me of a story from a decade or so ago…
    The Fire Service Institute at the University of Illinois produced a video of a fire test of engineered lumber joists with OSB webs. In their setup, a weighted floor system with a fire below collapsed in 4 minutes with engineered joists, and lasted 30 minutes with dimension lumber. The Wood Products Association called a meeting. I was invited as a friendly outsider.
    The wood people complained that the engineered joists were overly dry and the dimension lumber was overly wet—good points. The Fire Service Institute complained that the burn properties were unknown for the engineered wood. I was asked to weigh in, and mentioned that my field is moisture and we do not know the vapor permeance or the change in structural properties when wet. At which point a young participant from a wood products manufacturer chimed in saying “Oh, we don’t have any mold or water problems with our products, we provide a wax coating to protect the panels…” at which point all eyes turned to him, and one of the firefighters asked “You slather your products with WHICH petroleum distillate?”
    Afterwards at the bar it turned out that all the firefighters build homes in their spare time and they all prefer using engineered joists to dimension lumber.

  46. albertrooks | | #46

    Reply to aj builder comment 46
    aj, If it gets stuffy, occupants can open a door. There are studies that talk about the volume of O2 in homes and how long it can take to be dangerous. The process is so slow that you have time to react. It's not like burning charcoal where occupants are replacing O2 with CO and unaware of the quick change.

    If the HRV fails then occupants are still safe, yet they now live in the 1970's. Not bad on a summer weekend.

  47. albertrooks | | #47

    Bill that was on topic.
    Was the wax coating covered in the above posts? I did not see it but might have missed it.

    Nice story Bill.

  48. wjrobinson | | #48

    Albert if ACH approaches zero
    Albert if ACH approaches zero and the HRV malfunctions ...? That's not good right? Are there alarm systems employed? CO2 monitors well placed? VOC concerns?

    Sounds like too low an ACH could and possibly should be corrected with passive air inlets or?

    Albert, no way does a sealed box = a 1970s home. How the heck are you in the PH business and say that? One is ACH 10-20 and one is ACH 0. One has whole house natural air changes in minutes or hours and one has no air change until a door is opened and left open? And I am talking doors closed, for example sleeping. Are the owners to wake up, feel like they are drowsy and then open doors till they figure out why? IF the HRV stops functioning a 0 ACH home I would think is in trouble sooner than later if well occupied and small.

    I'm not talking about imminent death but am talking rather super high C02.

  49. user-626934 | | #49

    Another anecdote... understanding from Gary Nelson at The Energy Conservatory (air-tightness testing equipment manufacturer) is that their calibration chamber is made from.....

    (drumroll please)...


  50. user-1026988 | | #50

    Daniel, Interesting stuff.

    Thanks for the anecdote. For what it is worth, I have spoken at great lengths with engineering at Huber and pretty much every other company that make sheet goods. Not only about the wood products used in the northern v. southern mills but also about MDI resins, PUF's, changing permeance of different products relative to RH, saturation rates,structural properties, and the reality that they misguided consumers by implying on their website at one time that zip sheathing has a PERM rate of 16. ( they have since added an asterisk to the statement to specifically denote that the coating Green and red is 16 PERMS) I like Huber products. Advantec is simply a superior product to regular OSB, no doubt about it. It is also 3 times the cost and isocyanates are toxic. This has always been a clean material choice v. cost decision for us.

    1 ATM = 14.7 psi = 103000 Pa. 50 pascals or KPa is not a lot of pressure. It simulates maybe 20 times exterior ambient conditions. It is really not a lot of pressure. The bottom of a swimming pool exerts more pressure. So does the wind.

    That being said, in the 10+ PH that we have site built and the 4 that we have manufactured we have never had a blower door test come back higher that .44 ACH 50. That is also using the EIN 13829 testing standard which is less forgiving that the ASTM volumetric calcs. Some of these homes used OSB as the sole airtight layer, but most used a combination of OSB and fabrics such as proclima's Intello.

    I have often wondered if we should just switch to zip sheathing or advantec but I have just not been able to justify the cost. I will continue to re-think.

    This is an conversation that I have been having for a long time with a lot of different folks.

  51. RZR | | #51

    Back to the entertainment and fun! Log in worked, not banned yet ;)

    Martin Wrote: It is perfectly possible to build a house with poured concrete walls and a carbon-fiber roof -- as well as a $50,000 engineering budget.

    Martin, I have noticed often you pull out portions of my post to challenge or make fun of since you can not address the technical aspects and contents due to your lack of knowledge and experience in certain areas. I respect your knowledge and appreciate it greatly but, you do not know it all. You also like to call out my post as "off topic" a few times now, when they are spot on topic, while you do not many other poster such as AJ builder for just one example. There are MANY post that are far off topic all over this site. By doing so you are sending a bad message to your readers. If you are going to call people out for being "off topic" I suggest to apply the rule to all readers and not single people out that know more than you in certain areas. I have been doing alot of this for decades all over the world, if it bothers you that I have gained some valuable knowledge I share that's your problem....again you are sending a bad message to your readers that is entirely up you, not my site. You may want to work on the accuracy of addressing the technical content of my post since there is no way in he## incorporating carbon into a home design would cost a "$50,000" engineering budget". It has been done for so long now including building's there is no need for anymore design budget than OSB....there is plenty of allowables, span tables, properties available to not have to take the material into a lab to develop it. Obviously, you have never been a part of developing material properties or designing to them too. You spend too much time trying to find fault in my post, it becomes foolish!

    Word of caution: Do not build the box AJ builder described, waste of time. To test out OSB air seal life cycles and manufacturing quality a proper hot box test would need to be conducted. I recommend if there any questions about a manufactures ability to produce OSB such a test by a professional third party is required. It is done all the time in this industry and many more. AJ builder as proven once again he has no idea what he is recommending to the GBA readers, trash! If he's not bringing the Dreamliner into off topics he relating cell cheap cell phones to cheap OSB, now writing DIY hot box test plans for GBA......My, my, and Martin finds him "on topic" I guess, lol! I love this site!

    Keith Wrote:

    What makes me think.............
    If there is that much variance in airtightness, what is the variance in strength?

    I mean, air barrier is a secondary consideration, OSB is supposed to be a structural material, if the manufacturing varies that much......

    This is an EXCELLENT question that did not get answered so I will. Structures should be the first consideration very in sight full on your part, many have lost sight of with this energy efficiency craze.

    It depends on the magnitude and type of load, but in general small voids or delaminations will not have a large impact on structure if designed with the proper margin of safety(IE: 2-3). This is why we have positive margins for manufacturing or design anomalies. If designed with a negative margin voids can become more of issue. Code has the margins or allowable which means limit or operating load is safe if you follow code. The manufacture should identify them and fill them, a question you could ask them when shopping around, or ask to see test results and inspection paper.

    Peter L: You are being unnecessarily harsh on SIPs.

    Yes I was because I have designed better skins than fiber(wood, glass, carbon,) reenforced plastic and foam sandwich construction. SIPS will surpass a stick(panel brakers is what they are) on and OSB shear web in air sealing and structures by far! The dual adhesive bond lines are redundant for an air barrier, the bond lines are the (nails) which resist shear and tensile much better. Racking? Bending, SIPs is much better. The panels, sub assemblies that is. Large loads will transfer from the subs to the installation fasteners that can result is large bending, worse case being high seismic or wind, so, the sub-assembly installation fastening will be critical as well as air sealing these gaps. We can find good and bad history on most building methods, it just depends on the design and environment they are proven or not proven in.....

    A step up to SIP is no installation gaps and fastening, monolithic structure such as concrete or continuous homogeneous mass.

    Wood type has nothing to do with voids, again, it is the manufacturing process. The wood IS the "filler" in a bed of resign. The only "filler" or additive or transport should be oil....You could make 100% plastic sheathing with the same properties, no problem, but more expensive. Fillers in most bonds are used to take down cost in this case resign or fill with no purpose but to create a void. The silica content of wood will have a part in the bond to the catalyst or binder which is critical, but the proper ratios and types of phenol-cat-oil will bond to most any wood....they use OSB since they can take any scrap wood and make a product cheap, good engineers can find ways to make any wood problem, trust me. Hemp fiber due to it's higher silica content and tensile strength would be a top performer if it were more available. The longer and stronger the cellulose strands the better, no different than glass or graphite. Continuous stands such as cloths or uni-directional tapes have the best properties including a reduction in voids and delams due to an even load distribution of cross sectional areas.

  52. rdhvicenergy | | #52

    Vapour Barriers
    SIGA Majpell has a vapour permeance of 0.5 Perms. Applying it as an air barrier on the exterior of a stud-cavity insulated wall assembly in a cold climate places a vapour retarder on the cold side of the assembly. Why were other products not considered?

  53. GBA Editor
    Martin Holladay | | #53

    Response to Robert Lepage
    At the Passivhaus in Scranton, Pa., the OSB you see in the photos was on the interior side of the insulation. Once the air leakage problem was fixed, the builders installed vertical I-joists on the exterior side of the OSB sheathing (installed like Larsen trusses). Insulation was later installed between these I-joists. That means that the Siga Majpell ended up on the interior side of the wall insulation.

    This type of wall is called a Klingenberg wall. (For more information, see The Klingenberg Wall.)

  54. rdhvicenergy | | #54

    Response to Martin
    Ah, it's one of those beasts. Thanks for the response Martin.

    If they weren't intending to use a membrane as part of the air barrier, where they intending on using the OSB as vapour control? I'm not as familiar with my American building codes, but as I recall, the IRC would require a Class II vapour retarder in a CZ 5 (?) with a ventilated cladding over plywood sheathing.

  55. JFink | | #55

    Great article, Martin!
    Great article, Martin! Thorough as always, and very interesting!

  56. GBA Editor
    Martin Holladay | | #56

    Response to Robert Lepage (Comment #54)
    Scranton, Pennsylvania is located in Climate Zone 5.

    The International codes require walls in Climate Zone 5 to have a Class I or Class II vapor retarder on the interior side of the insulation. In other words, the vapor retarder must have a permeance that is less than or equal to 1 perm. (For more information on this topic, see Vapor Retarders and Vapor Barriers.)

    There is a "ventilated cladding" exception in the code. The exception is poorly written and open to interpretation, but the exception appears to allow a Class III vapor retarder to be substituted for a Class I or Class II vapor retarder if the wall includes ventilated cladding.

    Some sources report that OSB has a permeance of 0.7 perm, meaning that it would qualify as a Class II vapor retarder. Other sources, however, report that most OSB has a permeance of about 2 perms, making OSB a Class III vapor retarder.

    Anyone who is uncertain of how these code provisions will be enforced should consult with their local code enforcement official.

  57. RZR | | #57

    Good Article
    I finally took the time to read the article. You do a great job at writing and pulling info together Martin.....I don't have that skill set.

    Nothing I stated above changes.....

    Niall: Thread had more listing of credentials, personal experiences, than good test data. A debate on which glue to apply where, but again no real data.

    Belgain Lab Test: This is a limited air permeability test that lacks world-wide environmental loads and conditions. A low budget test a manufacture would do to establish an air perm rating. I'm just amazed at how conclusions are drawn by "Building Experts" and Engineers without the proper testing and simulations of field conditions, especially when the design relies on glue. You don't have to look far into other industries to see that adhesives, especially room temp cures, that are subjected to fatigue as a result of temperature, pressures, chemicals, do not last long. OSB temp and pressure cure combined with room temp cures tapes, sealants, on a job site by any level of skill....does anyone see the problem here? You will find in any maintenance manual a schedule of periodic seal inspections based on failed test data from proper testing (just look at your automobile). It is very difficult and costly to test and isolate the many OSB, seals, and sealants, in a world class field test study to create accurate standards, so we are left with personal opinions from so called "Experts"....I never design to that.

    "Lap" tension and shear are two well known properties used for adhesives and tapes the manufacture should have a 3rd party bench test on the data sheets, not once mentioned anywhere. That is a begining for tapes and gives an indication how strong they are. Primers, others tactics, only according to the tapes installation manual and test data, not opinions.

    The test data you are looking for as a reliable source of design information is professional hot box testing that properly test field conditions, not just pressure. No more than pressure alone or perm rating's are a reliable source of data to draw conclusions from, or when and why OSB will fail, a blower door test only proves the home is Passive or whatever at the time the test was taken. It lacks all fatigue testing conditions too that the home will also experience over time.

    The most obvious way to conclude this lack of data is do not design to it or use it, including all the band-aids that are not fully tested either. If you do, due to the variables (including workmanship) and unknowns, there is no way of telling Mean Time to Failure (MTTF) or reliability data (Mean Time Between Maintenance, Replacement, MTBM, MTTR...there are formulas for this goggle it) and fatigue life cycles will be. No OSB or tape manufacture is exempt or better than the other from the proper lab testing and field data by a third party.. Anything less is guess work based on limited personal experiences anyone can draw from just use goggle.

  58. wjrobinson | | #58

    Zip tape installed at low temperatures
    Just for you Terry, the tape around the windows of this local house is peeling off this week.

  59. leighadickens | | #59

    @44, AJ builder, I can't believe you actually said that
    I know I'm late to this party, but I just have to say, about AJ builder's comment #44...

    Dude, your comment that "even a woman could do this" is quite inappropriate for this forum. There are quite a few women in the building industry, and as a rule, most of us don't appreciate having to listen to colleagues say crap like that, even in jest, as it just reinforces ideas we should be done having to fight, already. This is not the 1970's, ok? This is a place for professionals to meet and discuss ideas, and a comment like that in this forum when I'm trying to glean some interesting discussion is inappropriately unprofessional, and actually pretty hurtful. GBA editors, shame on you for letting someone make a comment like in this forum that un-contested. Remember that your audience is more diverse than you realize, and this is something you want to encourage, not discourage.

    As to the rest of the discussion: interesting stuff. I've got nothing much to contribute, aside from a desire to see more research on this, especially over time. We've always gone with CDX for structural reasons, as we're designing for very high wind zones.

  60. GBA Editor
    Martin Holladay | | #60

    Response to Leigha Dickens
    I apologize to GBA readers for not addressing AJ Builder's comments promptly. Such comments are entirely inappropriate, and my failure to address the comments should not be seen as endorsement.

    I have recently been quite busy challenging this type of stupidity -- most recently in regards to comments posted here: Energy Efficiency Is Narrowing the Stupid/Hurt Gap. I had to challenge a reader who blamed engineering problems on a company that hired a "woman manager" to "fill a quota," and then I had to challenge another reader who said that women are different -- they aren't attracted to mathematics like men are...

    So, it's been a discouraging week in the misogyny department. Thanks very much for your comments, Leigha. I'll try to stay ahead of the Neanderthals in the future.

  61. RZR | | #61

    In my defense
    Leigha, you will also find in the thread Martin referenced that he took what I wrote out of context. His efforts to let AJ builder take it too far, get away with anything from attacks on women to being far "off topic" on most threads I addressed above.

    My woman lead Engineer was with me when we laughed at the 3rd level woman that was incompetent and the job Boeing put her was clearly above her head, MANY people agreed, she eventually got let go. AJ builder high jacked that thread with a Dreamliner post Martin allowed that got it all started, now in AJ defense to blame and point the finger at me. I didn't blame her for that, it was clearly Boeing's fault as I posted. It happens, men, women, any ethnic group, my memory and example just so happen to be a woman. Martin and AJ turned it into something I did not intend.

    Your right in the fact that Martin allows AJ to get away with things he does not others until someone brings it to his attention. Thank you. I bet you are a better builder than AJ "builder"...whatever his real name is.

    BTW: My wife in an Engineer too. I know first hand how competent some women are, and men. We both have rehabbed many homes ourselves for decades, the two of us, now our son in a family business.

  62. Expert Member
    MALCOLM TAYLOR | | #62

    Take heart
    The last two university commencement ceremonies I went to (one for Law) were seas of pony tails with nary a male in sight. Individual attitudes may persist for a while but change in the professions is occurring, and occurring quickly.

  63. svglass | | #63

    Air permeance data for North American OSB in fact do exist

    I know you value measured data (and non-neanderthalic comments that stay on topic), so I thought you should be aware that the National Research Council (NRC) of Canada has published air permeance data for North American OSB products.

    The ASHRAE Handbook – Fundamentals includes air permeance data for three North American OSB products. The source of the Handbook data is an ASHRAE-sponsored research project that was completed in 2002 by NRC Canada. The project was titled, “A Thermal and Moisture Transport Property Database for Common Building and Insulating Materials.” This research project measured hygrothermal property data for roughly 40 materials in the laboratory. (As an aside, some of the material property data in WUFI’s North America database come from this project.) A summary of the project with a description of the materials and an overview of the properties can be found here:

    The full report is available (for a fee) here:

    Here’s the take-home message. First, a brief description of the three products.
    OSB 1: This product is available as 4’ X 8’ boards at a nominal thickness of ½”. The strands of this product are manufactured from poplar and aspen. The bulk density is (650 ± 30) kg m-3.
    OSB 2: This product is available as 4’ X 8’ boards at a nominal thickness of 3/8”. The strands of this product are manufactured from balsam, poplar and trembling aspen. The bulk density is (660 ± 30) kg m-3.
    OSB 3: This product is available as 4’ X 8’ boards at a nominal thickness of 7/16”. The strands of this product are manufactured from birch, poplar and aspen. The bulk density is (650 ± 30) kg m-3.

    And here’s a summary of the OSB air permeance data, with values converted to the same units that you’ve used in the article.
    OSB 1: 0.005 L/(s.m²) at 75 Pa
    OSB 2: 0.006 L/(s.m²) at 75 Pa
    OSB 3: 0.013 L/(s.m²) at 75 Pa

    Clearly all measurements were below the 0.02 threshold for an air barrier material. By the way, this project included three plywood products, all of which met the air barrier material definition.

    Another related project at NRC Canada was the “Moisture in Exterior Wall Systems” (MEWS) project. Again, lots of property data for lots of materials. See the “Summary Report from Task 3 of MEWS Project at the Institute for Research in Construction - Hygrothermal Properties of Several Building Materials” available here:

    Page 23 of the report lists measured air permeance values for plywood and OSB, stating, “Both products are very airtight materials.” A range is given based on six different OSB products and six different plywood products, with measurements on three test specimens of each product. The OSB products had bulk densities in the range 575 to 725 kg m-3 and varied in thickness from 10 to 11.5 mm. The strands included aspen, poplar, birch, and southern yellow pine, though the report does not specify which product included which species.

    Plywood: Air permeance varied between 0.00013 and 0.010 L/(s.m²) at 75 Pa.
    OSB: Air permeance varied between 0.00066 and 0.014 L/(s.m²) at 75 Pa.

    In summary, all the North American plywood and OSB lab measurements are below the threshold [0.02 L/(s.m²) at 75 Pa] for an air barrier material. Of course, this does not mean that all North American OSB products currently on the market meet the criterion. But given the fact that all the Canadian laboratory data point in one direction, and the majority of builders’ experience confirms that passive house levels of air tightness can be achieved with OSB as the air barrier, you would do well to revise your article to be more balanced. I think you're intelligent enough to figure out what needs fixing, so I'll stop here.

    Sam Glass
    USDA Forest Products Laboratory

  64. ntisdell | | #64

    So there is some good data, that is more then a decade old...

    Possibly when OSB was still made with "old school" methods and quality?

    Now with green and 'lean' manf efforts maybe things have changed?..."aaah we can use less glue/resin"...." look it still passes strength test"... "look at that cost savings..."

    Could just be a few bad batches also....

    I guess in the end it's not a spec'd or tested attribute of OSB - on top of that a very high majority of builders and home owners have no idea about this (or why it would be important) (...can't say i've seen taped OSB or taped fiberboard on any home I see go up)

  65. GBA Editor
    Martin Holladay | | #65

    Response to Sam Glass
    I'm very grateful for your comments, and for the links you provided to valuable papers.

    I'm delighted to learn that more data exist on this topic, and will revise my article to reflect the findings you cite.

    Thank you very much.

  66. Cjb80 | | #66

    OK then..
    Assuming that I can build a cube where 5 sides are made out of plywood and the 6th side is made out of OSB and all seams are taped, what equipment would I need to test how air permeable a sheet of OSB is? I think it would be good to come up with a guide on how to build a test setup and perform the test so that we can gather data on (currently available) OSB products.



  67. [email protected] | | #67

    Out of context ??
    Terry, here's something to ponder. You would have been fine if you left the word woman out of the sentence. Think about it. Think of the response you would have had if instead you said Black manager or Mexican manager or Muslim manager. In my opinion the word manager is enough.

  68. dankolbert | | #68

    Some of my best friends
    are engineers.

  69. [email protected] | | #69

    Osb,Zip tape, rain and the engineer
    Zip Tape, Zip Sheathing and OSB
    Here are my experiences with Zip tape, Zip sheathing and OSB. Zip tape was applied with the Zip tape applicator in the cool of the morning. By mid- afternoon the wall heated up and the Zip tape was hot and wrinkled due to expansion from the heat. How air tight is wrinkled Zip? I don’t know so I decided to remove the wrinkled Zip tape. I then reinstalled the tape during the heat of the day with the tape in tension. No more wrinkled tape. So my question to anyone who has an understanding of the properties of Zip tape is:
    •How many houses out there, built using Zip tape are leaking air more in the heat of the summer?
    •How long will Zip tape remain in tension to avoid the wrinkling in the heat?
    Osb and rain- After a few heavy rain the edges of ½” osb are now 5/8”-11/16” thick. This can’t be good. To the engineers out there, have you looked closely at the edge of ½” osb that is now over 5/8” thick. The glue is starting to fail and the osb is starting to unravel. Does this osb make for a good long term shear wall? I didn’t think so. Off came the osb and on goes the Zip. Zip got me through a very wet winter with no issues except a little bit of swelling at the nails. Osb swells with a few rain storms, Zip not so much. Does lack of resistance to moisture in osb correlate to unacceptable air leakage? My guess is probably not but how many folks building super tight want to take a chance. Are you going to test every sheet of osb? Not me, a dollar save is not a dollar earned, in this case. Can industry make a high quality osb at a decent cost? You bet they can. They can also put a stamp on the back saying “air barrier approved”.
    Hurrary for Martin, another great blog. Ps I have a 1/2" piece of plywood blocking the overflow in my pond. Its been there for 25 years. Little to no delamination and measures .52 ".

  70. RZR | | #70

    Hot box testing
    "Now with green and 'lean' manf efforts maybe things have changed?..."aaah we can use less glue/resin"...." look it still passes strength test"... "look at that cost savings..."

    I remember the "lean" buzz word birth about ten years ago.....Where do these clowns get this crap from, not discriminating against clowns btw....The idea to lean out the assemble line with less tooling such as jigs as here it comes.....AJs (assemble jigs) would that be nice less AJ ;)

    While the clowns were in the dog and pony shows I was on the shop floor working on tool designs with mechanics.....By the time they were out we had reduced non-recurring cost further in one hour more than the time charge to the meeting. The concept of "lean" is manufacturing applied (lean out the assy line) and recurring cost, but it does happen in design by now the lack of blue prints that have made a mess out of production, and some computer CAD_CAM technology. OSB manufacturing uses this technology, the bigger companies you are right, probably to cut cost anywhere possible without reducing quality of design-build is the intent. It is really no different than they way we have done things for decades, only that clowns sell managers buff word processes that get us no where.

    "Assuming that I can build a cube where 5 sides are made out of plywood and the 6th side is made out of OSB and all seams are taped, what equipment would I need to test how air permeable a sheet of OSB is? I think it would be good to come up with a guide on how to build a test setup and perform the test so that we can gather data on (currently available) OSB products."

    This is a hot box test set up of a seal that was leaking under atmospheric loads, I was the Project Engineer, wrote the test plan and final report. The insulated metal box has the seal in it's assembly inside with a sight glass, we had test and instrument Engineers on it too. We accelerated the test to 30 year life cycles based on the conditions it had in the field, we tried to simulate. The black line is CO2 for temps +/- 100 F as required, we had send and return lines for humidity, pressure, chemicals, control, feed into a PC program. Before we get too far, you are going to need alot of time and money to do a proper test, and some help by professionals. As I said, pressure and perm rating's are not enough, it would be if all OSB seen was pressure and moisture that degrades in life over time.

  71. Expert Member
    MALCOLM TAYLOR | | #71

    I may be wrong but my understanding is that neither Martin Holladay or Dan Kolbert own hot boxes, so perhaps they should in future refrain from commenting on building materials. Further, neither are qualified chefs so perhaps it would be best if they didn't do any cooking for guests or host barbecues.

  72. albertrooks | | #72

    Thank you Sam Glass
    Sam, That was very useful data. Thanks very much for posting it.

    Is there data available on the materials used in the formation of the OSB? I'm still stuck on wondering if it's the wax coating or?? that is the differences between the OSB products quoted. An understanding of this would help those who might want to specify a product or family of OSB products to be used as an air barrier. It does so well as an AB in so many cases.

  73. wjrobinson | | #73

    comment #44 is in support of women!!
    It was sarcasm to do with Terry.... For frivolity folks.

    We all have serious needs and hopefully can relax and smile amongst friends.

    I build. PH has a cost issue with me at least. I also am willing to do things myself. PGH is me. I can do it for much less cost for about the same result. If it can be afforded sure I respect those who prefer PH. Still even if I did PH work I would own a blower door . And if I used OSB, then I would build a simple test box. Some disagree, fine, we disagree.

    Not a PHD, I build. I love building. I appreciate all people even Terry. And I joke here. Sorry will try harderto make my sarcasm clear for the serious amongst us.

    So how many ajbuilders does it take to screw up a sarcastic post? One!

    Sam Glass, excellent on topic useful post. Shows the value of plywood and OSB too.

  74. RZR | | #74

    Lack of data
    ZIP Tape:

    Siga Tape:

    Tensile Lap: We are interested in tensile strength or pulling the tape off the bond(lap) to phenolic resign-cat-oils found in OSB, not of the tape itself.

    Shear Lap: Shear resistance at the lap (bond line) from building or OSB movement.

    Both acrylic neither list the basic critical properties so we can not answer ,

    How many houses out there, built using Zip tape are leaking air more in the heat of the summer?

    How long will Zip tape remain in tension to avoid the wrinkling in the heat?

    Because the proper hot box test has not been conducted and shown on the data sheets...Answer is unknown, unless someone can BBQ the stuff and figure it out ;)

    I'd personally stick with the same OSB and tape manufacture, less risk. It will function best at the install temp, again no real data on temp, pressure, moisture, salts, acids, etc exposure.

    Some companies bleed resign and catalyst to the edge to protect or add a layer to protect the wood from rot, not reinforced with a fiber, so it will not take much to delam or void an edge.

    Hey MT good to see you join the family fun, BBQ your place, dog and pony show? Pin the tail on the AJ?

  75. GBA Editor
    Martin Holladay | | #75

    Response to Debra Glauz
    There are many kinds of testing. I performed an outdoor test of Zip tape for 10 months, and reported my findings here: Return to the Backyard Tape Test. I tested Zip tape on OSB, plywood, housewrap, and XPS.

    Others have performed similar tests: Peter Yost performed some informal testing and reported his results on the BuildingGreen web site. John Straube is performing on ongoing outdoor tape test.

    The type of testing that Terry Lee describes is useful, especially when the results are shared by tape manufacturers. In the absence of good published data, however, builders have to resort to tests like the one I performed. We are a community of learners, and we all need to share what we know.

  76. RZR | | #76

    Back Yard Testing
    True, I have been testing some natural building materials I really struggle finding any pro-test for.

    Most pro-testing test several mechanical and thermal properties. Your thermal test was is your climate zone which of course can differ. The next time you do this, I suggest you add a lap shear test from substrate movements that happen in building's that are structurally restricted. That would entail some simple Engineering to figure a way to test the adhesive bond line in the transverse direction, or shear wall from racking, etc, by pulling the panels apart laterally. You'll more than likely find that shear is lower than the tensile test you did on the bond line. Compression is not applicable with tape bond lines, but it is in line with tension usually.

    Had some strain gages been under the adhesive one could calculate values for tension and shear in PSI. Those nominal values get knocked down due to insulation debri (sawdust, etc) or a safety factor.

    See attached: ESR 1473, Zip test configuration. If you are going to test a manufactures product you do so in accordance with the configuration and test parameters they set up. Get their baseline, change the gap, the nail schedule, the pressure delta(orientate the panels different in back yard to the wind, or use a fan, higher wind on one side means lower pressure to put the bond line in shear and tension), see what happens in tension and shear. If this configuration varies in the field (which we know it will since their test was performed in a controlled test environment with little to no installation errors) per ZIP installation instructions, one could expect variations in air seal. That is aside from Huber's OSB and tape detailed quality control issues, if any.

    Zip video "tape it last" is interesting. According to it there is "cross link" chemical bond that happens with their adhesive-to-osb, instantaneously I'll add as most chemical reactions are. They claim that bond has been "engineered" to not deteriorate over time compared to others. In that respect, if gets stronger over time, however, I know some binders such as lime are said to increase the mechanical properties(tension, shear, values) over time but, I have never seen proof or a value at installation, others over time, in any of the film and foam adhesive data sheets I have looked at. I think it is probably some tapes degrade over time more than others, from the sun, elements.

    Here is an example of the type of pro testing and studies that are needed.....all over the internet,

    This report presents an experimental evaluation of three different test configurations to
    determine the suitability of the techniques for generating shear data under cyclic fatigue
    loading conditions. Single-lap, tapered-strap and scarf joint configurations were
    considered. The test methods were evaluated in terms of fitness for purpose in assessing
    fatigue performance and provides a guide to specimen geometry, manufacture and testing.

    "Stress analysis of an adhesive lap joint subjected to tension, shear force and bending moment"

  77. user-1071391 | | #77

    OSB air barrier
    I'm disappointed to see so much off-topic ranting in the GBA blog. I have had more respect for most of what I have seen here.

    Of course I realise that this is also off-topic.

  78. GBA Editor
    Martin Holladay | | #78

    Response to Daniel Hagan
    I don't know if you are referring to my article or the posted comments.

    Needless to say, posted comments always vary in quality. It's an unfortunate fact of life.

    Sometimes you have to sift through a lot of ore to find the nuggets. Since this article contains comments by the likes of Christian Corson, Daniel Ernst, Andrew Michler, Albert Rooks, Bill Rose, John Semmelhack, and Sam Glass, I can't complain.

  79. Richard Beyer | | #79

    Terry Lee.... This is brilliant!
    "Green Foam Advisors....since it is the solution to most problems out here ;)"

    "OSB-FOAM-OSB ....Now we talking GBA talk ;) SIP it up, or ZIP it up, your call ;)"

  80. wjrobinson | | #80

    Martin simple works. My post
    Martin simple works. My post to me is worth mentioning, which is don't use the lowest quality sheathing if quality is important.

    Zip, plywood, Plytanium are better products or add an air barrier wrap, done.

    Very frustrating to see people put huge effort into building a home... which one has to to build to PH standards and then see such a push back against OSB when it is such a low cost component of a build if chosen. To me it's like buying the lowest cost car and expecting it to perform like cars sold for the high level of value not price. It just plain does not make sense to a partial degree engineer that has built many a plane and home and has gone through all it takes to learn aircraft mechanics to certify two experimental aircraft. It's like the person who I had to sell a few dozen AN bolts to that needed them not because he said he lost them, no because tight is good tighter is better till he started snapping bolts, AN hardware has fine threads and one can easily torque till they snap.

    OSB is OK. It is not tops. I respect my opinion and others should respect and know such. It is not the best product to sheath with.

    On topic? IMO exactly on topic and the best most practical direction to go tomorrow. If someone comes up with stamps and certifications, then we can revisit then. Tomorrow is here now, make a wise choice.

    And absolutely the names mentioned are highly valued by myself and all.

  81. GBA Editor
    Martin Holladay | | #81

    Response to Terry Lee
    All over the country, builders are performing blower-door tests. In some cases -- perhaps just a few, or perhaps many, because we don't know how many cases there are like Pedranti's -- leaky OSB may be making it difficult to attain blower-door targets.

    There are several reports from Europe, and now one from the U.S., that air is leaking through some samples of OSB.

    Builders want information on this issue. I want information on this issue. Currently, OSB manufacturers are neither providing information on the air leakage rates through OSB, nor are they testing their products for air leakage.

    This article attempts to share with builders the information we know.

    You write, "The article is flawed and lacks conclusive data." That is your opinion. But the data I report is accurately reported, and I have never claimed that the OSB industry has released conclusive data. One of my points, in fact, is that conclusive data are lacking.

    If this type of reporting strikes you as "flawed," you are of course welcome to your opinion. But some builders are interested in the issues discussed here.

  82. RZR | | #82

    Lack of Data
    Richard, I'm pretty sure that makes me a top poster like yourself :) Malcolm's "qualification's" post was the best and takes first place for the best poster.

    The article is flawed and lacks conclusive data.

    1. Blowing air into a box is not enough of a hot box test to determine when and how OSB will leak air in world wide environmental load conditions. The article does not address the proper testing to determine this.

    2. Lap shear and tensile determines an adhesives ability to sustain the test of time, none of the adhesive manufactures show this data on their sites. The back yard test Martin performed did not even test shear the weaker property that cause failure, more less bending-misalignments, installation anomalies that are common in building's across America and the world......A lack of data to determine what adhesives are best. Assuming adhesives 'get stronger' over time is not supported by manufactures of adhesives.

    3. Using primer and membranes to ensure air seal of tape and OSB has not been properly tested for world class applications.

    AJ, you seem to be a great guy with a great attitude. When you are wrong you do not attack people or do all you can to fault find their post or create rant like some out here. I value your post and every ones. I don't have a list, I thank everyone for their contributions....I'm not qualified in some areas to determine who is right or wrong or "top posters" that make the best contributions. You have seen me post that I seek experts as required. I will however tell you when I think you are wrong and I expect the same in return. That is what makes up a good forum, getting to correct data no matter how many ego's need crushing including mine, shoes need to be stepped on, or teeth need to be pulled. No matter who you are, the posters and readers make these sites successful, without them they do not exist. You can find inaccurate info anywhere, plenty of that out there.

    BTW AJ: Aircraft have not been assembled with mechanics torquing nuts and bolts for decades. Steel "hi-loks" or lockbolts very strong(100,000 psi tension) are used, see below and the one with the yellow collar at top. The way it works is a gun holds the bolt shank with a pneumatic allen wrench that inserts into the tip (threaded end) (the tip has a hex (female) like a allen-key insert (not shown in the pic) . The gun torques the collar (or nut, the rustic color one), until the reduced shank(shown in the pic) breaks off at the proper torque. This allows blind installation or from one side (in other words, no need for two wrenches). This takes human error out of the equation other than drilling which there are very sophisticated drill guides or, the big companies use auto-drilling and fastening by gantry and CNC. The gantries cost in the mutli-millions.

    You can get them "encapsulated" with a sealant collar to air seal, common in areas subjected to atmospheric loads, just like homes. The aircraft is pressure tested just like homes, after manufacture and in the field at scheduled maintenance. Data is collected for design purposes.

    AJ I got my FAA A&P mechanics license back in 1982, Northrop U, Inglewood, CA..worked few years and race cars decided it wasn't for me.

    It's good to see aircraft and where some have already taken and are still trying to take the building industry of the future :)

  83. RZR | | #83

    Well it is flawed...
    and I never pointed to anyone including the manufactures as fault. First, in-order to review were the issues are you have to properly identify them. Lack of manu data is just one. I provided great detail on the manufacturing process and the exact properties that lack for the specific products brought into the discussions.

    From a design perspective (and I already stated this) ....You do not design to unknowns, period. If you do you do not understand what you are doing.

    From a build-blower door test perspective, do not confuse this with life cycle data. It means very little that you got passive house cert with OSB and membranes. Sustainable data once again lacks over time.

    So if you are out for a reliable design-build life cycle, due to the lack of data OSB and tape is not a robust solution.

    I believe AJ stated all that first post.

  84. wjrobinson | | #84

    Terry off topic but... my planes are not airliners
    I build experimental aircraft, hang gliders, ultralights. We use two wrenches and old fashion AN hardware and even low quality pop rivets, along with higher quality pop rivets, some glues, some tapes.

    A tape failure tried to kill me one time. Didn't as you can see. Covering on a tip blew loose and inflated a bay of the wing. I had just enough rudder to counter it, just enough. Used up at least 9 lives flying all these aircraft around the country.

  85. Expert Member
    MALCOLM TAYLOR | | #85

    Thinking about the longevity of tape over time: Has anyone used a flexible caulking on the unsupported horizontal edges of the sheathing with or without tape?

  86. chuck77 | | #86

    Test box
    Comment #66
    I'm down for the DIY test box idea. Good idea, I want to test the OSB for my own build. I'll give some thought how to instrument this.

  87. wjrobinson | | #87

    My box idea. 2' square. Seal
    My box idea.

    2' square.
    Seal sample edge with European tape
    Test box with plex panel for how air tight.
    Add valve and manometer test port
    Sig tape sample to box.
    Pump out 6 cu inches of air (50 Pascal) and the test with and without a sheet of poly over OSB.

    Play with it till info is useable.

    Have scrap of this articles OSB shipped in to sample.

    Would be fun possibly useful.

  88. GBA Editor
    Martin Holladay | | #88

    Pedranti's OSB
    Richard Pedranti saved samples of the Weyerhaeuser OSB from the Scranton job, and he is now in discussions with one or two labs to see if one of the labs can test it for him.

  89. ErgoDesk | | #89

    Fact: OSB is Quality Crap, so everyone go use some.
    I demand seeking an OSB to Particleboard comparison article.

  90. AdamMark | | #90

    All about Air Testing
    Great post. Really looking forward to read more.

  91. RZR | | #91

    Proper Testing

    Leave the testing to the pro's....Read this sample standard test report, there is no need to reinvent the wheel(standard format) that has been turning for decades in massive quantities for MANY products. We have enough inconclusive amateur testing. If you don't completely understand this test (and it is basic) you have no business writing a test plan for even part of it, or communicating with a lab.

    Take note of the big fish manufactures that were involved and that funded it. The entire test starts with professional representative(s) that are capable of communicating requirements (usually a manufacture that fully understands the design, manufacturing, and installation processes) of the product, to generate a requirements document in writing that is used to develop, with the lab professional(s), an initial test plan that can change as more is learned, just like this test changed in the process (ie. induced air gap sizes to simulate the field better). Those professional manufactures have the burden of proof and are the ones you want to do business with, since they are looking for answers to improve the quality of their products and have nothing to hide...They fund projects like this with thier own R$D money to build a name, so do universities that have the knowledge and funding. The same needs to happen with different manufactures of OSB/tapes for world wide applications, or America. Perm rating's are not going to cut it, an accelerated comprehensive fatigue life test cycle (30 year min) needs to be performed by third party, and the final test report made available to the public. Anything less is a complete waste of time but, feel free to have fun.

    Martin's article provided some good field level test I thought were pretty it, again, no need to reinvent the wheel.

  92. travis71 | | #92

    We've tested and inspected THOUSANDS of homes at the framing and final stage and I've always said I could build a home WITHOUT ANY EXTERIOR SHEATHING and get it to pass a tight blower door test requirement because the drywall is the actual pressure boundary. I can't believe that this OSB is leaky enough to significantly impact the blower door reading of a fully finished home where the actual pressure boundary is sealed tightly. I'm not saying it's wise to have leaky exterior sheathing, I just don't agree that it is the major factor in determining the air tightness of the home.

  93. GBA Editor
    Martin Holladay | | #93

    Response to Travis Dunn
    Evidently you are a proponent of the Airtight Drywall Approach (ADA). That approach has been used for decades, and it works. But it is not the only way to create an air barrier.

    The ADA approach requires a lot of caulk and the use of airtight electrical boxes. Many builders have found that when the air barrier is moved to the sheathing layer, air sealing work is simplified. Moreover, this change allows electrical wiring to occur inside the home's air barrier, greatly reducing the number of penetrations that need to be sealed.

    You wrote, "I can't believe that this OSB is leaky enough to significantly impact the blower door reading of a fully finished home where the actual pressure boundary is sealed tightly." Your disbelief is based on a misconception. The homes experiencing this problem aren't using the ADA approach; rather, the OSB layer is the "actual pressure boundary."

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