Wall Sheathing Options

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Wall Sheathing Options

Choosing between OSB, plywood, fiberboard, rigid foam, diagonal boards, and fiberglass-faced gypsum panels

Posted on Nov 20 2015 by Martin Holladay
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For the past 30 years, the majority of new homes in the U.S. have been built with wood-framed walls sheathed with oriented strand board (OSB). Most builders are so comfortable with OSB wall sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. that they never consider using an alternative material.

In fact, a wide range of materials can be used to sheathe a wood-framed wall. In addition to OSB, builders can choose plywood, fiberboard, rigid foam, diagonal boards, and fiberglass-faced gypsum panels. If you’re a dyed-in-the-wool OSB user, it might be time to consider some of the available alternatives to OSB.

It’s sheathing, not “sheeting”

Before we compare different sheathing materials, we need to clear up a common misconception. Plywood and OSB are examples of sheathing, not “sheeting.” The word comes from the verb “to sheathe,” which means to encase something in a protective covering (as a dagger is protected by a leather sheath).

Builders who talk about “sheeting” apparently assume that the word is derived from the word “sheet” (as in, “a sheet of plywood”). These builders are wrong.

Sheathing serves many functions

No one has yet invented the perfect sheathing material. Ideally, a sheathing material should:

  • meet code requirements;
  • be affordable;
  • be strong enough to brace a wall (provide racking resistance);
  • hold nails and screws well without being so dense that nails and screws have a hard time penetrating the material;
  • be airtight (or able to be rendered airtight fairly easily);
  • be vapor-permeable;
  • be easy to install quickly;
  • be a "green" material that can be produced locally from recycled or renewable raw materials.

If you know of any material that complies with these properties, send me an e-mail.

OSB. OSB panels are made of large wood chips and glue. OSB is strong enough for wall bracing, and holds fasteners well. The main advantage of OSB over alternative products is its low price.

If OSB can be kept dry, it performs well. In cold climates, most types of wall sheathing go through regular cycles of wetting and drying; the moisture content of sheathing is typically relatively high in February and relatively dry in May. Some building scientists wonder what 50 years of this type of moisture cycling will do to the structural integrity of an OSB panel; time will tell.

If OSB gets wet and is unable to dry out fairly quickly, it swells irreversibly and then begins to rot. Of course, most types of wall sheathing — including plywood sheathing and board sheathing — will rot if they get wet and stay wet. But when exposed to persistent moisture, OSB rots faster than plywood.

In a paper on mold by Joseph Lstiburek, Nathan Yost, and Terry Brennan (“Mold: Causes, Health Effects and Clean-Up”), the authors explain, “Mold … likes processed wood better than it likes real wood. So mold likes oriented strand board (OSB) better than plywood and plywood better than a stud or a joist.”

Lstiburek expanded on this point in a Fine Homebuilding article called “The Mold Explosion: Why Now?”, noting, “OSB is the Spam of mold food. Because we peel and flake the tree, we can use smaller trees that are faster-growing and contain mostly sapwood. If you’re mold with the choice between 2x4s and OSB, which are you going to choose? OSB, every time.”

Builders who have had problems with OSB rot sometimes switch to one of the high-quality OSBs manufactured by Huber Engineered Woods. Huber makes both AdvanTech sheathing and Zip System sheathing, either of which can get wet without swelling like ordinary OSB.

Zip sheathing is a type of OSB with a special exterior facing (an overlay of kraft paper impregnated with water-resistant resins). Zip sheathing is much more water-resistant than other types of OSB, and that’s a good thing. Moreover, the Zip System approach includes a high-quality tape for OSB seams; once taped, the Zip sheathing layer is close to airtight and can even function as a water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (WRB).

However, AdvanTech OSB and Zip OSB cost quite a bit more than ordinary OSB, so anyone who specifies one of these Huber products isn’t getting the same cost advantage that most OSB purchasers enjoy.

Plywood. In the U.S., plywood was the dominant wall sheathing material for wood-framed walls from the early 1950s until the late 1980s. Like OSB, plywood is strong enough to brace a wall and holds fasteners well. Plywood has a proven track record for use as sheathing.

Plywood mills require high-quality logs with few knots. To make CDX plywood — the most common sheathing grade — softwood logs are rotated on their axis as a long, very sharp knife is used to slice off thin veneers. These veneers come off the log like sheets being pulled from a roll of paper towels. The thin veneers are then flattened and glued together, with the grain of each layer oriented at 90 degrees to the adjacent layer.

When exposed to enough moisture for a long enough time, plywood will rot — but not as fast as OSB will. Manufacturers of OSB point out that inexpensive brands of plywood can have problems with delamination or voids. That’s true, but these problems are rare with the more established plywood brands. In general, plywood has fewer performance problems than OSB. Of course, it also costs more.

Fiberboard. According to the North American Fiberboard Association, fiberboard “is a fibrous-felted, homogeneous panel made from ligno-cellulosic fibers – usually wood – which has a density of less than 31 lb/ft3 but more than 10 lb/ft3. Fiberboard is characterized by an integral bond which is produced by interfelting the fibers, but which has not been consolidated under heat and pressure as a separate stage in manufacture.” Many brands of fiberboard sheathing are impregnated with asphalt. Fiberboard has a measurable R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. ; most manufacturers report that 1/2-inch fiberboard is rated at about R-1.3.

Ordinary fiberboard sheathing isn’t strong enough to be used for wall bracing. There are fiberboard products rated for wall bracing, however; these are referred to as “structural fiberboard.”

North American manufacturers of structural fiberboard include:

One of the main advantages that fiberboard has over OSB or plywood is that fiberboard is more vapor-permeable. Depending on the brand, fiberboard has a permeance of between 5 and 28 perms. This high permeance allows a fiberboard-sheathed wall assembly to dry to the exterior more quickly than an OSB-sheathed wall or a plywood-sheathed wall.

One of the main disadvantages of fiberboard sheathing is its tendency to belly out when a builder installs dense-packed cellulose or blown-in fiberglass between the studs. In 2011, I interviewed Mark Dixon, who helped install fiberboard wall sheathing on a PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. residence in Olympia, Washington. Dixon told me that the fiberboard wall sheathing was unable to resist the pressure of the dense-packed blown-in fiberglass insulation. After the insulation contractor finished insulating the walls, the fiberboard had bellied out and was bulging as much as 3/4 inch in some stud bays. The workers eventually managed to force the bellies back, at least partially, but the experience revealed one potential drawback of fiberboard sheathing.

A Maine builder, Chris Corson, has this to say about fiberboard wall sheathing: “It worked; it did its job. But it’s difficult to work with. It’s hard to install. It’s dirty. It smells like asphalt. When we started installing the cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection., it really bellied out. Fortunately we caught the bellying before it became a big problem. We finished the job by watching it closely and babysitting the insulation contractor.”

Fiberboard sheathing can’t hold nails or screws, so siding needs to be installed with long fasteners that extend back to the studs, or to vertical furring strips installed over the studs.

For more information on fiberboard sheathing, see The Klingenberg Wall.

[Photo credit: HP Builders / YouTube]

Rigid foam. Builders who install a continuous layer of rigid foam insulation on the exterior side of their walls often install the foam over OSB or plywood sheathing. However, it’s also possible to skip the OSB or plywood, and to install rigid foam as the only sheathing material on the wall.

The main advantage of this approach is that the rigid foam provides a continuous layer of insulation that interrupts thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through the studs. It’s also an affordable approach, because you don’t need to install any OSB or plywood.

Any of the three most common types of rigid foam — polyisocyanurate, extruded polysturene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.), or expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) — can be used as well sheathing. Because of its relative fragility, EPS is rarely used for this purpose unless it is fully supported by OSB or plywood. Green builders prefer polyisocyanurate to XPS, because XPS is manufactured with blowing agents that have a high global warming potential. Foil-faced polyiso is the easiest type of rigid foam to tape, which is another reason it is often chosen for use on walls.

Builders in cold climates need to make sure that any rigid foam wall sheathing is thick enough to keep the interior surface of the rigid foam above the dew point during the winter. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

Anyone who wants to install rigid foam wall sheathing without any underlying OSB or plywood needs to come up with a method for bracing the walls. Here are four possibilities:

  • You can install a few strategically placed pieces of OSB or plywood (usually at the corners) to stiffen the wall.
  • You can install 1x4 let-in bracing.
  • You can install L-profile metal strapping.
  • You can install a few inset shear panels.

For more information on these bracing methods, see Four Options for Shear Bracing Foam-Sheathed Walls. Note that most of these methods require the help of an engineer, and that some of these methods don’t meet code requirements in high-wind areas.

For more information on fastening details for rigid foam and flashing details for foam-sheathed walls, see How to Install Rigid Foam Sheathing.

Rigid foam won't hold fasteners. To facilitate the attachment of siding to a foam-sheathed wall, most builders install vertical furring strips between the rigid foam and the siding. (Of course, the furring strips also create a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap which helps the siding dry quickly.) These furring strips are installed at 16 inches o.c. or 24 inches o.c., and are fastened to the studs with long screws. The siding is fastened to the furring strips.

Some types of siding (including vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). siding) can be installed directly over rigid foam, as long as the foam is no more than 1 1/2 inch thick. With this type of installation, the siding is fastened through the rigid foam to the studs with long nails or screws.

Builders who are considering the use of rigid foam sheathing may also want to consider the use of nailbase panels. For more information on this topic, see Nailbase Panels for Walls.

[Photo credit: Robert Swinburne]

Diagonal boards. Diagonal board sheathing was quite common in the U.S. before World War II, and the method is still used occasionally in rural areas of the U.S. In northern New England, affordable rough-cut spruce, fir, or pine boards — usually 1x6s or 1x8s — are commonly available at local sawmills.

Diagonal board sheathing has a lot of advantages for green builders: it’s usually produced locally; it’s strong; it’s vapor-permeable; it resists rot better than OSB; it holds nails well.

Diagonal board sheathing has three main disadvantages: it’s labor-intensive to install; it can’t be used as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.; and many building inspectors won’t accept the use of boards that lack a grade stamp.

Builders who install diagonal board sheathing usually let the boards run wild at window rough openings and corners. Once the wall is sheathed, the builder snaps vertical and horizontal lines where necessary and cuts off the wild ends neatly.

Fiberglass-faced gypsum panels. While fiberglass-faced gypsum panels like DensGlass Gold have long been used on commercial jobs, this type of sheathing is relatively rare on residential jobs.

Fiberglass-faced gypsum panels are structural (they can be used for wall bracing), fire-resistant, and vapor-permeable (23 perms). Some brands of fiberglass-faced gypsum, including DensGlass Gold, can be exposed to weather for up to 12 months. Because this type of gypsum panel is paperless, it is unlikely to be attacked by mold.

Unlike OSB or plywood, fiberglass-faced gypsum panels are not designed to hold fasteners: “All siding must be attached through the DensGlass sheathing and into the steel or wood framing.”

A recent web search shows that DensGlass Gold costs about $20 per sheet.

No sheathing material is perfect

All of the sheathing materials mentioned in this article a can be successfully used to build a quality home. The key to a durable wall is good detailing.

Good wall design requires careful consideration of the vapor permeance of all the layers making up the wall assembly. Dry sheathing is happy sheathing. Walls need to be detailed to limit moisture accumulation (either from the exterior or the interior) and to encourage rapid drying. Good wall details include high-quality flashing and a ventilated rainscreen gap between the sheathing and the WRB.

Martin Holladay’s previous blog: “Where Does the Air Come From?”

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Image Credits:

  1. Image #1: Lunenburgfirehouse.blogspot.com

1.
Nov 20, 2015 1:19 PM ET

Fiberglass sheathing
by Bill Dietze

Martin,

A typo for you. Under the fiberboard heading you wrote:

"This high permeance allows a fiberglass-sheathed wall assembly to dry to the exterior more quickly than an OSB-sheathed wall or a plywood-sheathed wall."

Which is certainly true, but maybe not what you intended to say.

Bill


2.
Nov 20, 2015 1:50 PM ET

Response to Bill Dietze
by Martin Holladay

Bill,
Thanks for catching that. The typo has been corrected.


3.
Nov 21, 2015 2:17 PM ET

Fiberboard sheating + D.P. Cellulose DOA?
by Bill Dietze

So is the idea of using fiberboard sheathing with deep dense-packed cellulose walls dead? Anybody doing this who would do it again? Use 3/4" fiberboard? Does 16" o.c. framing help?
...Or just run away and keep running?


4.
Nov 23, 2015 10:02 AM ET

Response to Bill Dietze
by Martin Holladay

Bill,
No, the idea is not dead. Both projects that I describe worked -- the builders just had to wrestle the bellies back in place. You need to anticipate the problem and pay attention.

One other approach that some people use is to install two layers of furring to create the rainscreen: first horizontal furring (a layer that addresses the bellying problem) followed by vertical furring. That's more materials and labor, of course, but you end up with an impressively well-ventilated rainscreen gap.


5.
Nov 23, 2015 11:36 AM ET

Perfect Sheathing
by David Stuhlsatz

I suppose we'll find a perfect sheathing in the same country that has unicorns and perfect HVAC systems.
I wonder if Huber is working on a "Mark II" version of their insulated Zip system, but I doubt it would meet an affordability criteria.

A rigid foam product with good shear performance, fastener acceptability, and some degree of vapor permeance would be useful. "Compac" foam as a sheet good might fit the bill.


6.
Nov 25, 2015 1:44 PM ET

Edited Nov 25, 2015 1:45 PM ET.

Felt faced polyiso
by Buzz Burger

This is not precisely a sheathing question but seems related; I think it is hard to overestimate the importance of keeping OSB sheathing warm (at least in a cold climate) which is one reason why I prefer loose fill plus a generous layer of exterior foam to double stud walls of equivalent R value (plus it deals with thermal bridging even better than double stud). Consider a 2 x 6 wall sheathed with OSB with a very carefully installed WRB on the exterior of the OSB (taped Zip, liquid membrane, or peel & stick). The idea being to use permeable loose fill in the stud cavities and a relatively permeable foam board exterior of the WRB (plus a ventilated rain gap of course) so that the wall can dry in either direction. Is there a problem using felt faced polyiso as the foam insulation board? You won't find it in big box stores but is readily available at roofing supply houses and it is much less expensive than the foil faced panels (I recently paid $17 for inch and a half R9 4 X 8 panels). I know that polyiso doesn't like to get wet and shouldn't be used below grade but it seems to me it should be okay with the ventilated rain screen and the lower cost will get you closer to double stud in your quest for max R per dollar. I've been to the manufacturer's website and it appears that it is not recommended for walls but I don't know why. My local roofing supply house didn't know either or why one side is labeled "this side up".


7.
Nov 25, 2015 1:55 PM ET

Edited Dec 7, 2015 6:48 AM ET.

Response to Buzz Burger
by Martin Holladay

Buzz,
You're correct that it's a good idea to keep OSB warm and dry, and that exterior rigid foam insulation is a good way to accomplish this goal. If you haven't seen it yet, you may want to read this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

If you have designed your foam-sheathed wall properly, there will be no need for the OSB or studs to dry to the exterior -- because the rigid foam will keep everything warm and dry. That's why it's perfectly OK to use foil-faced polyiso on the exterior side of a wall. Here's the idea: everything on the exterior side of the polyiso (the furring strips and siding) will dry to the exterior, while everything on the interior side of the polyiso (the OSB, studs, and fluffy insulation) will dry to the interior.

If you prefer to use polyiso without a foil facing, feel free to do so. (However, if you are installing a reservoir cladding like brick, the foil-faced polyiso is preferred, because it stops inward solar vapor drive.)

Your reference to peel-and-stick is confusing. Unless you are building a PERSIST wall without any insulation between your studs, use peel-and-stick with caution (unless it is one of the new-fangled expensive peel-and-stick products that is vapor-permeable). In general, it's safer to choose a vapor-permeable WRB like Tyvek or Typar than a peel-and-stick product for use on the exterior side of OSB wall sheathing. [P.S. For further discussion of this topic, see Comment #17, below.]


8.
Dec 3, 2015 11:09 AM ET

We use "Advantech"
by Robert Knight

Advantech is another Huber OSB product--but unlike regular OSB it doesn't swell when it gets wet--waterproof glue is used. We have had very bad experiences with OSB as wall sheathing--even when cut edges get painted, which they rarely do. Take a look at FHB's study of sheathing from some years ago when they put Advantech in its own category because it was so good. Sure it costs more, but this is the bones of the building. I like diagonal boards too--but our builders groan.


9.
Dec 5, 2015 8:54 AM ET

Edited Dec 5, 2015 9:05 AM ET.

non-foam options missing
by Ken Levenson

Martin,
Although you have a fiberboard section - you've focused on the N.A. derived asphalt impregnated direction and neglected another great set of wood fiberboard options, coming from Europe - two examples:
GUTEX from 475 here: https://foursevenfive.com/the-gutex-wood-fiber-board-primer-vapor-open-c...
Agepan from PeakBP here: http://www.peakbp.net/agepan.html

They are not structural either but provide very sustainable and fully integrated moisture and thermal protection. We are seeing growing interested in these products.

RIgid foam is given as the only continuous insulation option - but the fiberboards above as well as rigid mineral wool boards by Roxul or others - should be considered along side foam.


10.
Dec 6, 2015 1:22 PM ET

Peel and stick.
by Buzz Burger

I've become obsessed with air tightness and I mentioned peel and stick because I suspect that a vapor impermeable membrane is more air tight than a vapor permeable membrane. I would agree that all things being equal the ideal WRB would be air tight and vapor permeable. I am also aware that products exist that the manufacturers claim have those properties. But there are degrees of air tightness and it seems intuitive to me that the most airtight would also be vapor impermeable. If I'm not mistaken, vapor permeability relies on tiny holes -- too small for water to pass but allowing water vapor to pass. Would that not also suggest that very small amounts of air could also pass? I guess the real question is: would it matter? Would the amount of air be so small to be inconsequential? Or is there something different about vapor drive that allows it to work through microscopic openings more readily?

You correctly surmised that the inspiration for this scheme resulted from my reading about the PERSIST system. But it seemed inefficient to leave the stud cavities open especially since I really don't want to use 2 X 4's for exterior walls. So I reasoned that elements of PERSIST but with loose fill added in the cavities would work well, especially in a more temperate climate: air tight as possible at the WRB sheathing plane with windows mounted at that plane (in betweenies), loose fill to the interior side of the WRB and rigid foam to the exterior in an amount sufficient to achieve a total R value comparable to typical double stud assemblies (which would substantially exceed the minimum rigid foam over sheathing requirement).

Finally, wouldn't there be an inward vapor drive in the summer with the AC running in which case vapor impermeability would be advantageous?


11.
Dec 6, 2015 2:46 PM ET

PERSIST
by Buzz Burger

Following up on my previous comment to your reply. In your last paragraph you imply that a PERSIST style vapor barrier on the sheathing is only a good idea if there is no stud cavity insulation. But why? The principle of PERSIST, as I understand it, is that the wall can only dry to the inside therefore it is critically important to keep the sheathing and framing dry and warm (in the winter). This is accomplished by the vapor/water/air control layer and lots of rigid foam insulation on the exterior. So what happens when we add cavity insulation? The wall can still dry to the inside (we have been careful not to add a vapor retarder) and, as you pointed out in a recent article, we have provided some hygric buffering potential. What has changed slightly is that even with the same amount of exterior insulation the sheathing is now not as warm even though the total R value of the wall is greater. The wall can still dry to the inside but the possibility of condensation on the sheathing is theoretically greater. So your point is that a vapor permeable membrane would be safer since now we have exterior drying potential. I get that but would it really matter anywhere other than a very cold climate? Plus, if we are going to focus on keeping the sheathing warm (among other things) than this method is far superior to double stud in that respect.

For years I have been collecting building science energy nerd articles, mostly by you and Joe Lstiburek. Went back into my archives and reread Lstiburek's perfect wall article from 2008 in which he suggests putting all the control layers on the sheathing and rigid foam on the outside and, for a residential wall with wood framing, cavity insulation (except in extreme cold climates). Again, I am not talking about code minimum amounts of exterior foam. I'm thinking in terms of 50/50, at least R40 with 20 interior and 20 exterior.


12.
Dec 6, 2015 3:26 PM ET

Buzz
by Malcolm Taylor

If you aren't using the wall cavities for much of your insulation, why don't you want to use 2"x4"s for the exterior framing?


13.
Dec 6, 2015 3:43 PM ET

Martin, You assert (in
by Skip Harris

Martin,
You assert (in comment #7) that using peel-and-stick is problematic (unless building a PERSIST wall), but also say that foil-faced insulation is fine as the wall will dry to the inside. Wouldn't the peel&stick work fine, too, as long as the wall has plenty of exterior foam to keep it warm? Is there a problem with a PERSIST-like wall that also includes cavity insulation, as long as the ext foam keeps the sheathing warm?


14.
Dec 6, 2015 4:30 PM ET

Reply to Malcolm Taylor
by Buzz Burger

I want to do advance framing which in most cases means 2 X 6's @ 24". Plus 2 x 6's tend to be straighter and nicer to work with. But actually, I do want to use the cavity for some of the insulation. Loose fill fiberglass or cellulose has the lowest cost per R value which is why so many super insulated houses rely on thick, double stud wall construction. For various reasons, I don't care for double stud wall. A 2 X 6 wall @ 24" centers with loose fill insulation and 4" of poly iso will have a higher nominal R value than a 12" thick double stud wall with loose fill. Plus I believe it deals with thermal bridging better and therefore the effective R Value will be closer to the nominal. Plus it lowers the risk of condensation on the sheathing by keeping it warmer. Also, it works well with positioning the windows on the same plane as the sheathing which I think has some advantages. At least this is what I have concluded after much consideration. Haven't actually built one this way yet but intend to soon and welcome any opposing opinions from any double stud advocates.


15.
Dec 6, 2015 5:09 PM ET

Buzz
by Malcolm Taylor

That make sense I was just curious. I think though that with the amount of foam you propose for the exterior, I'm not sure the advantages of Advanced Framing are worth the downsides.


16.
Dec 7, 2015 6:17 AM ET

Edited Dec 7, 2015 6:25 AM ET.

Response to Ken Levenson (Comment #9)
by Martin Holladay

Ken,
Thanks for your suggestions.

Very few American builders are using Agepan or Gutex sheathing from Europe, for two reasons: high cost and limited availability.

GBA first published a report on Agepan sheathing in 2011. (I was a guest at Albert Rooks' house in Washington when he took delivery of his first package of Agepan sheathing. It was shipped from Germany, of course. The photo below marks the occasion.)

If these brands of sheathing, or something like them manufactured in North America, ever become widely available and affordable, GBA will include them in lists like this and may consider recommending them.

As BuildingGreen noted in a review of Agepan Sheathing, "Much of the cost is in shipping from Germany. It currently retails in the U.S. at more than $17 for a 25" x 89-3/4" sheet of 5/8" DWD, or $1.10/ft2, and nearly $32 for a 23-5/8" x 74-1/2" sheet of 2" THD T+G ($2.62/ft2)."

As far as I can tell, Ken, from your web site (where your company, 475 High Performance Building Products, sells Gutex sheathing), Gutex must be ordered by the pallet (bundles of 28 or 54 pieces). This certainly complicates ordering and raises the chance for waste. The cost of the product ranges from $19 to $38 per sheet, before taking U.S. delivery charges into account.

I disagree with your contention that mineral wool boards should have been included in an article on sheathing. Mineral wool boards are used as insulation, but not sheathing.

.

Albert Rooks - Agepan sheathing.jpg


17.
Dec 7, 2015 6:44 AM ET

Response to comments by Buzz Burger and Dustin Harris
by Martin Holladay

Buzz and Dustin,
It's true that foil-faced polyiso, like Ice & Water Shield, is a vapor barrier. So if you design a wall with exterior foam properly, following the guidelines in my article on the topic (Calculating the Minimum Thickness of Rigid Foam Sheathing), then you can install Ice & Water Shield on the exterior side of the wall sheathing if you want. I think that step is expensive and unnecessary in most cases, but if you want a very good air barrier and a very good WRB, you can use Ice & Water Shield (or a similar peel-and-stick product) in that location if you want.

I hesitate to recommend that approach, however, because it can be misunderstood. (For an example of an owner-builder who installed Ice & Water Shield on the wrong side of the wall insulation, see my article, Dense-Packed Cellulose and a Wrong-Side Vapor Barrier.)

Most builders choose to install WRBs that are vapor-permeable for a good reasons: vapor-permeable WRBs are less likely to get you into trouble that WRBs that are a vapor barrier. But if you know what you are doing, and you include enough rigid foam on the exterior side of the Ice & Water Shield, then Ice & Water Shield performs very, very well.


18.
Dec 7, 2015 11:15 AM ET

Reply to Malcolm Taylor
by Buzz Burger

When you say "worth the downsides" are you referring to advanced framing? I am not aware of any significant downsides to advanced framing.


19.
Dec 7, 2015 11:28 AM ET

Response to Buzz Burger
by Martin Holladay

Buzz,
There are pros and cons to advanced framing, as this article explains: The Pros and Cons of Advanced Framing.


20.
Dec 10, 2015 8:03 AM ET

let's move the needle, not just just provide common practice
by Ken Levenson

Seems a waste to stick to "conventional approaches" - why not also show emerging alternatives, that if more fully adopted would lower prices. There are more options. Agepan is advertised on the home page of GBA, yet can't be included in a blog post?

Also, you are wrong about mineral wool. It can be used similarly to foam boards you show and have been - has illustrated in image 3 of 12 in this GBA blog post - http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/tale-...

We don't sell mineral wool - you should show it, imho.
Cheers.


21.
Dec 10, 2015 8:26 AM ET

Edited Dec 10, 2015 8:28 AM ET.

Response to Ken Levenson
by Martin Holladay

Ken,
I think that a fair assessment of GBA's role in promoting green building practices would show that GBA has been helping to "move the needle, not just promote common practice," as you put it, since the first day that our web site went online.

Many of the wall construction methods that you seem to favor, Ken, have been extensively covered here on GBA -- for example, in this article (which is #3 in the links provided in the "Related Articles" box on this page): The Klingenberg Wall. We will continue to report on a variety of methods for building high-R walls, including methods using exterior mineral wool, Agepan sheathing, or even no exterior sheathing at all.

Any GBA readers interested in articles on installing mineral wool insulation on the exterior side of walls may be interested in reading the following GBA articles (in addition to the one that you linked to, Ken):

Installing Mineral Wool Insulation Over Exterior Wall Sheathing

Installing Roxul Mineral Wool on Exterior Walls

Wrapping an Older House with Rock Wool Insulation

Mineral Wool Boardstock Insulation Gains Ground

Mineral Wool Insulation Isn’t Like Fiberglass

When selecting materials to include in my article on sheathing options, I made an editorial decision on which materials belonged in this category. In my judgment -- and I believe that most builders would agree with me -- mineral wool insulation is not a sheathing material. That doesn't mean that mineral wool isn't a high-quality insulation material. Mineral wool insulation is an excellent product that can be used to build durable, well-insulated wall assemblies.


22.
Dec 10, 2015 10:05 AM ET

the assessment was of the particular post
by Ken Levenson

not the GBA library.

I very much appreciate the wide variety of coverage the GBA library provides - and hope that such individual posts could also reflect a wider diversity of options.


23.
Dec 10, 2015 11:26 AM ET

Response to Ken Levenson
by Martin Holladay

Ken,
Green Building Advisor welcomes guest blog submissions. Such submissions can be sent directly to me at this email address: martin [at] greenbuildingadvisor [dot] com. We seek a wide diversity of opinions in our guest blogs.

As you know, Ken, GBA has republished blogs from your web site (475 High Performance Building), with your permission, including these:

Insulating an Old Brick Dormitory

A Straw-Bale Home in Vermont

We also try to publish guest blogs from other sources, reflecting the European Passivhaus approach that is championed by 475. See, for example:

An Insulated Cathedral Ceiling for a European Passivhaus

Five Different High-R Walls

Creating High-Performance Walls

High-Performance Walls, Part 2

High Performance Walls, Part 3

High Performance Walls, Part 4

The bottom line: we're all on the same page here. Keep those comments (and guest blog submissions) coming.


24.
Dec 10, 2015 6:17 PM ET

we appreciate being published on GBA
by Ken Levenson

and look forward to the continued dialogue. cheers.


25.
Feb 8, 2016 9:35 AM ET

no wall sheeting
by A Lange

I feel like this is a 'stupid' question, but I do seriously wonder why it is that wall sheathing is common practice (required?) in North America, but never (rarely?) used in Australia. I read the list of things that sheathing accomplishes and it does appear that they can all be accomplished perfectly well without sheathing. Not that I am implying that building is done particularly well in Australia. It is actually abysmally poor in regard to energy performance. The use of sheathing over an entire building (walls and roof) is one of the more striking differences in building styles I notice between the US-centric information online and actual practice here on the ground.


26.
Feb 8, 2016 10:43 AM ET

Response to A. Lange
by Martin Holladay

A.,
It's possible to build a house without any exterior sheathing, as you point out, as long as:

(a) An engineer designs or approves a method of bracing the walls. (Note that doing this without any wall sheathing can be a challenge in high wind or seismic regions.)

(b) The wall is insulated with an insulation material that is not air-permeable (for example, spray polyurethane foam) or, failing that, a durable airtight membrane is installed on the exterior side of the insulation. (Ironically, one of the best ways to provide an exterior air barrier is to install OSB or plywood with taped seams -- a method that you question.)

(c) The framers have anticipated the needs of the siding installers and window trim installers by installing adequate blocking. (It's quite frustrating to try to nail siding or window trim to air).


27.
Feb 8, 2016 7:57 PM ET

Response to Martin
by A Lange

Martin,
I was in no way suggesting I thought it was better to not use sheathing. It seems like such an easy thing to do that accomplishes so many things that are otherwise more difficult. It does save some material and therefore cost and I am guessing that is why it is done, but working on a roof that is not sheathed is slow and scary. Air sealing is only a consideration in the fringe building world, but maybe when that concept is embraced sheathing will be as well. Thanks for your input.


28.
Feb 9, 2016 9:00 AM ET

Response to A. Lange
by Martin Holladay

A.,
Thanks for your further comments. I don't know much about Australian construction methods, but I'm guessing that there are two reasons that Australian builders often omit the wall sheathing: (1) To save money, and (2) They don't care about air sealing or thermal performance (because the climate is mild).


29.
Jul 18, 2016 6:37 AM ET

Wall sheathing Direction
by James Barkman

Are there advantages or disadvantages to installing OSB or plywood sheathing horizontally or vertically?


30.
Apr 11, 2017 2:03 PM ET

Edited Apr 11, 2017 2:07 PM ET.

Downsides of Densglass
by Domenico Perrella

Martin,

Other than not holding siding fasteners, what are the downsides of using Densglass instead of plywood sheathing? A (modest) price difference? Is taped Densglass less of an air barrier than taped plywood?

I'm replacing an unsheathed stucco wall and will probably use plywood sheathing (I want no OSB in my house), but I'm curious about Densglass because I'd like to minimize the use of organic materials that can absorb lots of water or rot. I know densglass means that fasteners for the rainscreen material and sheathing need to be in the studs, which increases hassle and maybe labor costs, but I'm wondering if that's the only downside.

My wall would be (inside to outside) drywall, 2x4 framing with bays filled with Rockwool (sound is an issue and I'm trying to minimize wood/cellulose), sheathing (plywood, or maybe Densglass Gold), a highly permeable non-perforated WRB, possibly rigid insulation (1.25" roxul?) , but probably not unless the inspector requires it because the Northern California climate is mild, a rainscreen material like House Slicker or DC14 drainage mat), felt-backed metal lath, 3-coat stucco, paint.

Do you think DensGlass would be a poor substitute for plywood in that application? Also, what do you think of the DC 14? It has low permeability and the channels seem to be intended to create an air gap on either side of the material. I'm not sure if that's brilliant or scary.


31.
Apr 11, 2017 2:20 PM ET

Edited Apr 11, 2017 2:26 PM ET.

Response to Domenico Perrella
by Martin Holladay

Domenico,
I strongly urge you to post these questions on the Q&A page. That way more GBA readers will see your questions, and you are more likely to get feedback from our community of readers. Here is the link: Green Building Advisor's Q&A page.

-- Martin Holladay


32.
Apr 11, 2017 2:58 PM ET

Will do
by Domenico Perrella

Thanks, Martin. I'll post it there now.


33.
Apr 21, 2017 8:12 AM ET

Sheathing (WRB) vs Sheathing (Structure)
by Ethan T ; Climate Zone 5A ; ~6000HDD

The conversation above between Ken and Martin is illuminating, because I I think it gets to some of the confusion one encounters when thinking about high performance walls.

Martin provides a definition for sheathing in his article: "the word comes from the verb “to sheathe,” which means to encase something in a protective covering (as a dagger is protected by a leather sheath)." Despite this, most of the conversation about sheathing implies that it is providing shear strength...

However, in many high performance walls (Klingenberg, Corson, etc) we see that the "structural sheathing" has moved inside the wall and that what we would think of as the "dagger sheath" sheathing (Mento Proclima) has moved outside to the exterior face of the wall (inside the rainscreen)

The funny thing is that a housewrap actually resembles a "sheath" of some sort. As I have expressed elsewhere, I share the concern voiced by many of these unprotected membranes floating outside the wall as the last line of defense to rats, squirrels, and raccoons.

That being said, it seems that we have a distinct set of boundaries: Air Barrier, Water Resistant Barrier (WRB), and, potentially Shear strength layer (Shear layer?). The distinction as to which of these would be akin to a "leather sheath" perhaps leads me to consider that the very word "sheathing" is too vague to be considered a building product category... or perhaps it just needs to be continually qualified, as in "WRB sheathing," "Structural sheathing," etc.


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