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Need wall construction in Northern California advice

Amy (Homeowner) | Posted in Green Products and Materials on

I live in Northern California – 5 months of heating season – wet cold weather, no snow, rarely go below freezing. Dry summer and I don’t plan to have AC. I am planning on building a new house (around 3000 sf) with the following wall assembly. I am looking for advice on wall assembly with the following requirements:
A) healthy (not off gas and minimize toxic materials)
B) moisture control (allow the wall to dry should it get wet, minimize the chance of condensation, stop outside rain from entering the wall system). I don’t want mold growing in my wall.
C) good insulation for energy efficiency that is healthy and will last over time
D) Cost effective – I have limited budget and don’t want to spend more than 5% extra on green materials if possible

Question 1: SIP – I am assuming it’s more expensive than traditional framing and the SIP material will off gas. If I am wrong, please let me know if you know a SIP vendor I should look into in California.

I am considering the following wall assembly inside -> outside
– Safecoat primer and interior paint
– drywall (air barrier)
– dense packed cellulose in 2*4 and some 2*6 wall cavity
– plywood (no added formaldehyde)
– Some sort of EPS/XPS (additional R value) – optional (if it does not add too much cost)?
– Tyvek house wrap (air/vapor retardant),
– 2 layers of 30lb building paper (stop exterior rain soaking into the wall cavity) – I was told that building paper is cheap and good to have 2 layers for extra protection
– rain screen?
– wire for holding stucco?
– stucco
– exterior paint

Question 2: Does this assembly work well in my climate? What changes do you recommend? I am most concern about moisture and mold growing in a tight house. I am not sure how water vapor would travel through all these layers and where the water will be trapped and create potential mold problem. I like to allow moisture to escape out of the wall but not let the rain water in.

Question 3: Any specific products you recommend?

Question 4: Rain screen – I read about using 1″ wood strip to create air gap that allows water to drip down and avoid capillary action but the pictures always showing attaching the wood strip to sidings. I am using stucco, do I need rain screen or the building paper would protect the wall from water enough in my climate?

I read a post from Robert to use the following materials:
– Tremco acoustical sealant between each framing unit (bottom plate to sill, band joist to top plate, subfloor to band joist, bottom plate to subfloor, etc), and then apply Tremco on the inside edge of the top and bottom plates as the drywall is applied,
– Lessco polypans behind each electric box to allow sealing the drywall around those penetrations
Question 5: What additional products do you recommend using for sealing all the gaps and connections? Any other gaps (plumbing, phone/internet, etc) need to be sealed with different product?

Question 6: Do I need to insulate the cold / hot water copper/pex pipes in addition to the cellulose in the wall cavity? Can I assume the condensation from the pipes will be absorbed by the cellulose and dry up over time?

Thank you all in advance.

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Replies

  1. TJ Elder | | #1

    Amy, I would point out first that if you're going to have plywood sheathing, it's easier to make that the air barrier than to try and seal the drywall. Robert suggests that it's helpful to have the air barrier where you can inspect it (at the interior) but with airtight sheathing you can test it with a blower door during construction, before the insulation and drywall are installed. Any leaks that turn up at this stage can easily be fixed when the wall is open.

    The next thing that jumps out is that you say the house size is 3,000 SF and the most you'd consider adding for "green" is 5%. The numbers will improve if you trim the fat, and if green is at all a priority you could start by planning to build less house, then evaluate the budget for green features. In fact, making a small step toward "green living" does cost more, but making a big step costs less.

  2. Amy | | #2

    Thomas,

    Thank you for your quick response.

    I was told by my green point rater that the blow door test is done after the dry wall is up. If you find leaks then, you just seal them at that time. Why is it easier to seal the plywood sheathing layer rather than the dry wall layer? Is it because you can seal the connections (plumbing, electrical box, etc) easier?

    If the plywood sheathing layer is sealed as air barrier, don't you still want to seal the dry wall to avoid warm and moist conditioned air (in the winter) getting into the wall cavity that can may wet the insulation and increase the risk of mold growth?

    Regarding the size of the house, we have a lot of people in the house (kids, grandparents, relatives, etc) and also home offices and we need the space.

  3. Riversong | | #3

    Amy,

    I would also encourage you to design for optimum function in a smaller footprint. A well-designed smaller home can be more roomy than a poorly designed larger home.

    If you want a cost-efficient high-R wall, I would forget the foam and use flat 2x3 horizontal cross-hatching on the interior of the stud wall. That will increase the insulation cavity and dramatically reduce thermal bridging through the frame.

    All holes in the framing should be sealed with gunned foam (cheaper to buy a hand foam gun and canisters than the miserable-to-use and wasteful Great Stuff). The plumbing vent can be sealed at the ceiling with a roof flashing (just as you would at the roof) - this allows vertical expansion without losing the seal.

    Minimize penetrations through any insulated wall or ceiling (no recessed can lights) and plumbing should not be in exterior walls (but hot water pipes should be insulated). Use the low-expansion gun foam to seal around door and window frames, as well.

    Be sure to use a vapor retarder primer on all exterior wall and ceiling surfaces, such as Benjamin Moore Super Spec.

    Stucco is an excellent air barrier, so the Tyvek would be wasted. Use the double layer of grade D paper, or use the combination papered metal lathe for the outer layer. Be sure to use a drip screed and proper flashings.

    Wide roof overhangs and gutters are far better at controlling rain infiltration than rainscreens unless you're in a high wind zone.

  4. GBA Editor
    Martin Holladay | | #4

    Amy,
    I agree that you shouldn't expect Tyvek to be an air barrier. It is indeed easier to seal the plywood sheathing and make that the air barrier.

    You might still want the Tyvek, since there is lots of evidence that three layers of WRB are better than two when it comes to stucco. Even better, include an air gap between the plywood and the stucco. Read more here: To Install Stucco Right, Include an Air Gap.

  5. David Meiland | | #5

    there is lots of evidence that three layers of WRB are better than two when it comes to stucco

    Is this because stucco is incredibly good at absorbing moisture and holding it against your building so therefore you need all the WRB help you can get...? Or is there some subtlety I'm missing here?

    It's hard to see where stucco stands as a green building material. All the cement and quarried sand, to start with. Then there's what appears to be the dramatic likelihood that it will help your building rot, requiring expensive repairs. When I lived in Northern California I remodeled lots of older homes with stucco. Hot, dry climate, buildings with board sheathing, minimal insulation, and lots of air leakage. Stucco on new homes is a completely different thing in most parts of the country.

  6. Riversong | | #6

    Tyvek behind two layers of grade D paper will do nothing but waste money, unless there is bulk liquid water leakage through the stucco and both layers of building paper.

    Tyvek (perm > 50) is virtually transparent to water vapor, which is the primary mode of moisture transport from stucco into the sheathing and thermal envelope. A code-approved WRB must have a perm of 5 to allow drying to the outside by vapor pressure differential. Anything more than that makes the wall system too vapor open from exterior solar radiant drive.

  7. David Meiland | | #7

    Doesn't Dupont StuccoWrap have a perm rating of about 50?

  8. Riversong | | #8

    Yes. But why would anyone trust Dupont?

    This is the company that, according to the Center for Media and Democracy "has for decades knowingly manufactured dangerous products that now contaminate cities and has worked to undermine independent scientific inquiry and public policy when it runs contrary to DuPontis profits."
    Dupont also rivals Monsanto in producing genetically-modified organisms, including the "first crop genetically modified for increased consumer appeal" according to NaturalNews.com.

    If I use a plastic housewrap at all, I use Typar (12 perm) which was developed by the chemist who invented Tyvek and then left Dupont to manufacture a better product. If you remember, when Tyvek first hit the market it had to be quickly recalled because it began to deteriorate with as little 3 days exposure to sunlight (and would continue to deteriorate after covering).

    Good old #15 felt or grade D paper is still the best WRB and the one that the IRC specifies.

  9. David Meiland | | #9

    Believe me Robert, I don't use Tyvek for building although I did pick up some 3-foot rolls at a garage sale and used them for runners. It's a bit too noisy for that. Fortunately for me the local yard here has ASTM D226 15# and 30# felt. They also carry Typar and I guess I might use it in conjunction with Home Slicker.

  10. Riversong | | #10

    David,

    You can get Home Slicker Plus Typar as a combined product (probably a good marriage). I'm envious that your lumber yard has 226 felt.

    For those who don't know, 15 lb felt is no longer 15 lbs per square and 4869 is what lumber yards seem to generally carry:

    Felt Types lbs/square
    Unrated #15 felt 7.6 – 8.8
    ASTM D4869 #15 felt 8.0 – 9.7
    ASTM D226 #15 felt 11.5 – 12.5
    Unrated #30 felt 15.7 – 19.9
    ASTM D226 #30 felt 26.4 – 27.3

  11. David Meiland | | #11

    I've known about the Home Slicker/Typar product for a couple of years, but have a problem imagining it in action. With felt or wrap, you install the WRB first, then the windows and flashing, and then if you are using Home Slicker you install it last, and my experience is that there is almost zero waste with the HS material. If it were preattached to the wrap you would have to remove it at overlaps, where wrapping into openings, taping flanges, etc. It doesn't make a lot of sense to me, but I haven't seen it or used it. It is very quick and easy to install HS over the WRB just before installing siding.

  12. TJ Elder | | #12

    Amy,

    To revisit this issue of size and heat flow through the enclosure: If you're still designing, one thing to consider is geometric efficiency. Even if your program needs all the square footage you have planned, look closely at the shape and see if you can streamline to reduce the exterior surface area. A lot of suburban homes are designed to suggest generations of add-ons, with a variety of ins and outs and material changes. This gives more visual complexity than a dumb box, but you get iffy joints between intersecting walls and roofs, and extra surface area. Streamlined geometry is an example of improved efficiency that costs less rather than more, including less long-term maintenance from joints that might leak. Even with the same enclosed volume, if you cut 20% of the skin area, that will reduce heat loss just like increasing the insulation. Or again, use the material savings to make the remaining walls thicker.

  13. John Brooks | | #13

    Regarding the size of the house, we have a lot of people in the house (kids, grandparents, relatives, etc) and also home offices and we need the space.

    How many people will be living in this house "full time"?

  14. Amy | | #14

    Thank you very much for all your suggestions. Here is my modified wall assembly for healthy and breathable wall assembly:

    1. Interior paint - Ben Moore Natura
    2. paint primer - Ben Moore Natura
    3. drywall (air barrier)
    4. dense packed blow in borate treated cellulose (at least 3 lbs. per cubic foot -- 3.5 pounds is better -- to minimize settling)
    5. no added formaldehyde plywood
    6. Typar (12 perm) house wrap
    7. 30Lb grade D paper
    8. #15 asphalt felt
    9. galvanized (expanded metal) or fiberglass lath
    10. standard installation of three-coat stucco
    11. exterior paint

    A few questions left:
    1) Air barrier - should I seal the dry wall layer (so you can inspect it) or the plywood (so blow door test can be done before drywall up)? Or both?

    2) Robert indicated "vapor retarder primer on all exterior wall and ceiling surfaces, such as Benjamin Moore Super Spec.", I am not clear exactly where to apply the primer. Given that I already have 3 layers paper (Typar, felt, building paper), do I still need this extra layer of vapor retarder paint? If so, where should I apply the primer?
    - Drywall - the side touches insulation
    - Plywood - the side touches insulation and plywood
    - Plywood - the side touches house wrap

    3) Since I am skipping rain screen (see P.S. below), I figure it will be safer to have 3 layers of WRB. Since I don't know the capability difference among Typar/felt/paper, I figure I will use all 3 to be safe. Would you recommend different sequence from in->out typar->paper->felt ?

    4) Which of the following option has higher R value and cheaper to construct? Robert suggested "on the interior of the stud wall. That will increase the insulation cavity and dramatically reduce thermal bridging through the frame."

    - 2*6 24 OC
    - 2*4 18 OC + "flat 2x3 horizontal cross-hatching"

    Thank you all again and have a great Thanksgiving.

    P.S.
    - I decided against rain screen. http://www.benjaminobdyke.com/visitor/product/key/homeSlickerStone FAQ states "Leading building scientists recommend rainscreen systems be used in areas prone to wind-driven rain and/or areas that have an average annual rainfall of 40 inches or more". The annual rainfall is 15" in my area and I am not in high wind area.

  15. Riversong | | #15

    A few questions left:
    1) Air barrier - should I seal the dry wall layer (so you can inspect it) or the plywood (so blow door test can be done before drywall up)? Or both?

    Unless you're aiming for Passive House air tightness standards, you can wait to do the final blower door test after drywall and insulation are complete but before window and door and baseboard trim.

    2) Robert indicated "vapor retarder primer on all exterior wall and ceiling surfaces, such as Benjamin Moore Super Spec.", I am not clear exactly where to apply the primer. Given that I already have 3 layers paper (Typar, felt, building paper), do I still need this extra layer of vapor retarder paint? If so, where should I apply the primer?

    The vapor retarder always goes on the warm side - on the drywall surfaces of the insulated walls and ceilings.

    3) Since I am skipping rain screen (see P.S. below), I figure it will be safer to have 3 layers of WRB. Since I don't know the capability difference among Typar/felt/paper, I figure I will use all 3 to be safe. Would you recommend different sequence from in->out typar->paper->felt ?

    The industry standard for stucco underlayment is two layers of 60 minute grade D paper, not felt.

    4) Which of the following option has higher R value and cheaper to construct? Robert suggested "on the interior of the stud wall. That will increase the insulation cavity and dramatically reduce thermal bridging through the frame."
    - 2*6 24 OC
    - 2*4 18 OC + "flat 2x3 horizontal cross-hatching"

    Standard 2x6 framing is less expensive. 2x4 (16" oc is the standard, not 18") with cross-hatching is more material and more labor, but worth the difference for the reduction in thermal bridging.

    - I decided against rain screen.

    Good for you. It's become almost a fad that is used without considering whether it's really needed.

  16. Amy | | #16

    Robert,

    Thank you very much for your quick clarification and I am almost all set for the wall assembly except one question - "The vapor retarder always goes on the warm side - on the drywall surfaces of the insulated walls and ceilings."

    I just want to 100% sure I understand what you mean. Dry wall has 2 sides. (A) facing the living space that I will paint with beautiful colors (B) facing the insulation and studs

    Should the Benjamin Moore Super Spec be painted on (A) side as the primer for the beautiful paint color or (B) side on the back side of the dry wall that touches the insulation?

    I am not sure if it matters. If it does, I would think (A) is warmer than (B) in the rainy winter when the humidity is high; summer is very dry here.

  17. Amy (Homeowner) | | #18

    David,

    Yes, I did read the excellent blog from Martin. I admit that I don't always understand everything but I try to incorporate as much as I can (use plywood instead of OSB, at least 2 layers of paper, etc). I decided against the rain screen because I don't live in heavy rain/wind area.

    Am I missing something important that you can point out?

  18. TJ Elder | | #19

    Amy, the vapor retarder primer goes on the finish surface below the paint. It's the same idea as any primer, and should help even out the sheen on some types of paint.

  19. David Meiland | | #20

    Am I missing something important that you can point out?

    Probably not, but if it were me I would use a typical grade D application and add the air gap that Martin talks about in his article. You state that you're not in a heavy rain/wind area but I don't even know how that's defined, and unless you're in an arid climate I would seriously consider the air space, Robert's disagreement noted. You need absolutely perfect flashing and water details with reservoir claddings, so if you're skipping the air I would be certain that you understand those and that they are executed correctly on your house.

  20. Amy (Homeowner) | | #21

    Thanks for the additional suggestions. I think I am all set now. I am summarizing the layers below for potential future readers:

    1. Interior paint - Ben Moore Natura
    2. paint primer - Benjamin Moore Super Spec (vapor retarder)
    3. drywall (air barrier) - "final blower door test after drywall and insulation are complete but before window and door and baseboard trim."
    4. 2*6 wall with dense packed blow in borate treated cellulose (at least 3 lbs. per cubic foot -- 3.5 pounds is better -- to minimize settling)
    5. no added formaldehyde plywood
    6. 60 minute grade D paper, 30Lb paper
    7. Typar (12 perm) house wrap - If needed, add >= 1/4"" rainscreen
    "WaterWay rainscreen drainage mat, the Korax Stucco Rainscreen Panel, the Home Slicker Stone & Stucco rainscreen, and the Mortairvent mortar deflection and ventilation system" (from Martin's article)
    8. 60 minute grade D paper, 30Lb paper
    9. galvanized (expanded metal) or fiberglass lath
    10. standard installation of three-coat stucco
    11. exterior paint

  21. Riversong | | #22

    You state that you're not in a heavy rain/wind area but I don't even know how that's defined, and unless you're in an arid climate I would seriously consider the air space, Robert's disagreement noted. You need absolutely perfect flashing and water details with reservoir claddings

    David, if you had read the link that the OP offered, you would have that definition.

    From Benjamin Obdyke, a leading manufacturer of rainscreen products:
    "Leading building scientists recommend rainscreen systems be used in areas prone to wind-driven rain and/or areas that have an average annual rainfall of 40 inches or more".

    They noted that this quote came from “To Build a Better Home,” published by the APA-Engineered Wood Association, 2002, which included:

    "In areas like the Southwest that receive low rainfall (less than 20 inches annually), a housewrap or building paper should offer sufficient water resistance protection, according to most building experts. In areas that experience moderate amounts of rainfall (20 to 40 inches annually), protection against rain penetration should include an enhanced housewrap. And for wet and/or humid climates, coastal areas and hilltop exposures receiving high (40 to 60 inches annually) or extreme (60 inches or more annually) rainfall, a ventilated rainscreen assembly is recommended; a rainscreen system is also advised for areas that receive high winds in addition to rain. Rainscreen systems are recognized by leading building trade associations for their effectiveness in controlling rain water intrusion into wall assemblies in areas of high and extreme rainfall."

    This advice is similar to what is proposed in the HUD PATH manual Moisture-Resistant Homes: Best Practices Guide for Builders and Designers.

    It's simply not true that "you need absolutely perfect flashing and water details with reservoir claddings". What's needed is what has become standard industry best practice nationwide: two layers of 60 minute grade D paper. It was, in fact Joe Lstiburek who discovered that the outer layer of paper crinkled as the stucco cured, creating an "enhanced WRB" with drainage channels.

    Amy, what you need are two layers of standard stucco backing paper or one layer of polymeric housewrap and one layer of paper. You can also use any of the textured stucco substrates if you want additional drainage potential which is probably unnecessary in your rather dry climate. You're overly complicating this because you're getting so much conflicting advice, and you're getting conflicting advice because few building professionals really understand moisture dynamics.

  22. GBA Editor
    Martin Holladay | | #23

    Amy,
    While Robert is correct that two layers of 60-min. paper is the standard industry recommendation for WRBs behind stucco, our knowledge of stucco failures is evolving rapidly. Many areas of the country are plagued by wall rot problems behind stucco; in some cases, homeowners are on their second or third rebuild.

    It's your house. To me, an air gap between the stucco and the sheathing is simple insurance -- and it's so much cheaper than rebuilding your wall. Some of these rebuilds are costing $40,000 to $100,000 per house.

  23. Allan Edwards | | #24

    Martin

    As an alternate method and added insurance why not use 3 layers of WRB or the Huber Zip Wall product (counts as a WRB) with taped seams and 2 additional layers of WRB on top of the Zip Wall.

  24. Brett Moyer | | #25

    Three layers of WRB material seems excessive.

    Rainslicker is a great material but a bit pricey and perhaps not necessary for the climate in this discussion.

    The Huber Zip Wall product is also expensive and does nothing to address the drainage space between the stucco and sheathing.

    2 layers of 60-min. paper is the industry standard, but as Martin points out, an improved air gap is simple insurance and is worth the investment.

    I suggest a "crinkled" WRB such as Tyvek Drainwrap which will give you an air gap, and a layer of building paper which will add to this air gap and provide the necessary bond break between stucco and a plastic housewrap.

  25. Allan Edwards | | #26

    Brett:

    Since mid 80's I've built 75-100 pretty large stucco homes, using 3 WRB most of the time, I've never had one single problem with stucco. And I am in a pretty rainy area (Gulf Coast). The Huber Wall product is not much more than CDX. Maybe $500-$800/house. And the ability to tape the seams adds another benefit.

  26. Riversong | | #27

    If most of us agree that OSB is a junk product, perhaps we can also recognize that Zip Wall is just lipstick on a pig.

    Advantech might work for a subfloor, but Zip relies on tape and doesn't breathe (the Huber info is misleading on this and they won't divulge a perm for the combined material, though 3rd party testing indicates it's less than 1).

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