Air Sealing – Tape, Sealant?
I am looking at the articles here about air sealing and most of them provide information such as where to seal but the products are not so easily determined. I am planning on taping either the OSB Seams before house wrap with 3M All Weather tape – or possibly only taping the house wrap seams. (as long as I get the right tape that doesn’t allow problems with taped horizontal seams)
I am also looking at different types of sealants, and it sounds like a general acoustic sealant is the best pick. Is this true, or are there some other name brand products that I should be able to order online? I am thinking I would use it around any holes in ceiling/wall + between plates and under the window and door flanges.
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Replies
Nicholas,
For more information on tapes, see these two articles:
Return to the Backyard Tape Test
Air-Sealing Tapes and Gaskets
Note that in some of the locations where you are thinking of installing a sealant (for example, under the bottom plates of exterior walls), you might want to use a gasket.
When it comes to sealants, either Tremco acoustical sealant or a good brand of polyurethane caulk should serve you well.
To me it sounds like the 3m even on OSB will lose adhere ability over time. If I tape the house wrap with 3M will there be any benefit to taping the sheathing? Also, would it be labor beneficial better to install plywood blocking on the top plate of my interior walls that spans the gap between two truss chords or just plan on sealing drywall which butts against the top plate of interior walls...?
Nicholas,
Q. "If I tape the housewrap with 3M tape, will there be any benefit to taping the sheathing?"
A. It's far better to create the air barrier at your sheathing layer than at your housewrap layer. It's very hard to make housewrap airtight, because of all of the fastener penetrations and the difficulty of avoiding rips with contractor's ladders.
The reason you tape housewrap is not for airtightness; it's to limit water intrusion.
Either Siga Wigluv or 3M All Weather Flashing tape can be used to tape OSB seams, although the Siga Wigluv will perform a little better than the 3M tape.
Q. "Would it be better to install plywood blocking on the top plates of my interior walls that spans the gap between two truss chords or just plan on sealing drywall which butts against the top plate of interior walls?"
A. The usual way to seal the crack between your drywall and your partition top plates is from the attic, using canned spray foam. Another method is to install your ceiling drywall (and tape it) before your interior partitions are installed, so that the drywall is continuous.
The 3M and Siga Wigluv tapes are very good, I used both of them on our house in various areas. One functional difference I found is that the Siga Wigluv is more robust, not necessarily in the strength of the adhesion, but the strength of the tape material.
Again, both are great tapes, but I would trust the Wigluv to hold up better during the taping process. The Wigluv is more expensive though, so you'll need to keep cost in mind.
You can get the 3M from most building supply places and even Amazon:
http://www.amazon.com/3M-Weather-Flashing-Tape-Liner/dp/B00I2TUC3G
Wigluv is available, that I know of, from these two:
https://sigatapes.com
http://www.smallplanetworkshopstore.com
If you can't make up your mind based on cost and other factors, I'd suggest ordering a roll of each to test on your initial taping.
Does anyone ever tape where the foundation and sill rim joist area? I would think that would be a good place to air seal with tape. Is there a wider tape that would stick to concrete and wood/sheathing be good to use there. Any thoughts?
Brian or Martin,
Is the Siga Wigluv worth the extra price? I assume Wigluv 60 (2.4" wide) would be the proper product for sheathing. I'm just about ready to make the decision and start ordering tape and be the one crazy home builder who tapes the OSB seams (unheard of here). My main concern would be making sure it holds on until house wrap a few weeks from now --- but according to your tests in the backyard article, it would be fine for months.
Nicholas,
To me, Siga Wigluv is worth the price. Whether it is worth it to you depends on your airtightness goal and your budget.
I wouldn't worry about any problems related to weather exposure if you use Wigluv. But if you are worried, you can always install the Wigluv tape one or two days before you install the housewrap.
Mel,
Q. "Does anyone ever tape where the foundation and sill rim joist area?"
A. Yes, you can install tape to seal the crack between the mudsill and the concrete foundation, or between the lower edge of your wall sheathing and the concrete foundation. The best tape for this purpose is Siga Wigluv. Siga Wigluv will stick to concrete.
You're not crazy. You'll be the smart home builder who has a well air sealed house that is easier to heat/cool. Once you see how sticky these tapes are, you'll stop worrying about them holding for a few weeks or a few months...those time periods are not a concern.
No idea what the price difference is for you since I don't know how much tape you're ordering. If the difference was +/- a couple hundred dollars, then I'd get the Wigluv because it seems stronger and gives slightly more width. The 2.4" should be fine.
Not sure where I draw the line. Is sealing the OSB with tape a good economic move but not installing rigid foam because I deem that to be quite expensive...or am I thinking backwards and should install foam over OSB and not worry about taping any osb joints and forget that the added cost of foam is too much for my build budget.
Nicholas,
If I had to choose between airtightness and high R-values, I would always favor airtightness. That said, exterior rigid foam is usually a good idea, unless you live in a mild climate.
Martin, as per my post here: https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/43201/final-countdown-will-2-inches-rigid-foam-be-w#comment-98771
I am struggling with the additional cost of material, labor/time, and overall interest on the money used to insulate the house. Attacking airtightness seems to be something more affordable, and I was trying to tell myself it will be a better bang for my dollar. Possibly not in Zone 5.
Nicholas,
In Climate Zone 5, it would be a good idea to pay close attention to airtightness and to include rigid foam on the exterior side of your walls. But if you can't afford these details, you'll have to cut something: you can make the house smaller, for example, or choose simpler interior finishes -- or reduce the R-value of your walls. It's your choice.
Indeed. I already shrunk the house design :) It's about as small and efficient as design I could make.
In terms of foam, I can get DOW (yes, evil, I know...) at the local yard and may use that or EPS elsewhere. Either note, if I use DOW (xps...) can I get away with less thickness to make install go swifter? I was assuming 2" but I am reading 1.5" of XPS = the required R-Value for 2x6 cavity insulation to prevent condensation. I really want to use mineral wool batts for the walls if possible - may end up with dense fiberglass rolls but leaning towards mineral wool so the exterior R-Value calculation on foam needs to use those numbers to be safe. I think it's R19 or R21/22 (not true wall performance, I understand thermal bridging reduces it)
If I do foam, I will for sure only use 3M on the OSB if even that to reduce costs at all possible. Unless you are telling me I for sure need to use tape on OSB Joints even when using Foam!
If I can use 1.5" of foam instead of 2" it will be a tad easier to work with, but I will only do one layer. I would like 1.5" because I can use 2x4 stock lumber for all window and door frames versus 2x4 + additional ply to build out 2". If 1.5" of XPS is just borderline okay to keep my wall from having moisture problems, then I would just do 2" to be safe. I understand that EPS foam will require at least 2" if not more to be safe. Again, the foam itself is cheap in my calculations. It's all the additional materials, time, and effort to have the foam installed properly -- such as furring strips, window build outs, additional time siding instead of just nailing vinyl siding against OSB anywhere it will need to be on the strips, and flashing detail with the bump outs.
If you're going to be marginal on the exterior-R (especially if it's 1.5" XPS, which will be performing at less than R7 in 50 years) it's worth installing a smart vapor retarder on the interior for long term resilience.
You also might consider going with 2x4 / R15 studwall and 3.5" of exterior foam, using reclaimed roofing foam to hit the same wall thickness as 2x6 w 1.5" foam and a higher performance point, which would have huge dew point margin and likely lower cost. Reclaimed foam is typically 1/4-1/3 the cost of virgin stock goods. Both 3" and 3.5" are standard thicknesses for roofing foam.
With your 1.5" XPS and 2x6/R23 batts with 24" o.c. spacing you'd be running about R23 whole-wall.
At the same wall thickness, with 3.5" EPS you'd be at about R14-R15 for the continuous foam layer, and with a 2x6/R15 about R25 or slightly better whole-wall R.
Alternatively, with 3.5" fiber faced roofing polyiso (derated to R5/inch for age, climate and application, which is conservative- it'll do better than that) you'd be at about R17.5 -R18 for the continuous foam layer, and with the 2x4/R15 you'd be at about R28 whole-wall, which is quite a bit better than the 2x6 wall with 1.5" virgin XPS of the same thickness on both resilience and energy use, and probably a wash (possibly cheaper) on cost.
My walls are already set up (hints the question about taping OSB) and my walls are 2x6 16" O.C.
I figured 2" was the best choice to allow for deterioration of foam R-Value. Just means more work on openings and less rigid siding.