What air-seal caulks/sealants are now available?
user_6992381
| Posted in Green Products and Materials on
What caulks and sealants are currently available and recommended for air sealing walls and ceilings during construction?
My cabin is not new but I am stripping it to the studs and also installing new trusses, windows and doors. There will be 2 inches of XPS foam on the exterior and mineral wool in the 2 x 4 walls. Also 10 1/2 inches of mineral wool on the attic floor.
Is sealing the XPS with tape enough or should I also seal the OSB and all two-by joints with sealant? I want to use a sealant that will remain flexible and maintain a lasting seal.
Thank you, Tony
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Replies
Hi Tony,
Your question fell through the cracks but I'll answer, and hopefully others will as well.
There are many ways to make a house airtight, but the most common these days is with taped sheathing, often Huber's ZIP system (high-quality OSB with a waterproof phenolic coating), but CDX plywood can also work. Standard OSB can work but I've personally seen it fail as an airtight layer.
Rigid foam can be used as the airtight layer, but it shrinks a bit as it ages and/or with cold temperatures, so it's usually best to plan on a separate airtight layer somewhere in the building assembly. Henry Blueskin VP100 is a vapor-permeable, self-adhering membrane (Siga Majvest SA is another) that provide a WRB (housewrap) and airtight layer in a single product. Many other high-performance WRBs (aka housewraps) can also be used, with tape, as a system to create an airtight layer. Pro Clima Solitex Mento and Siga Majvest are two that I spec regularly.
Tapes are easier than sealants to install and verify for quality, but they also cost a lot more. For sealants that stay flexible, some people use silicone, which lasts forever but its seal to adjacent materials often fails eventually, so it's not the best material for this purpose. A product with a long history of working well is Tremco Acoustical Sealant. It's made from nasty stuff, so don't eat it, and it literally sticks to everything so be careful, but it works well. A product that performs similarly but that is a lot friendlier to work with is Pro Clima Contega HF. The stuff is like magic--it has zero VOCs but sticks well and stays flexible forever.
For wood-to-wood joints, you don't always need flexibility. I'm a big fan of PL Premium polyurethane adhesive. It's basically Gorilla Glue with fillers added, and I've used it successfully in very demanding situations. But in most cases it's safer to build in some allowance for material movement.
Plain old painted drywall makes a good airtight layer; you just have to be careful transitioning to adjacent air barriers, and to not fill the drywall full of holes. There are a variety of EPDM (rubber) gaskets available that can help, without VOCs and at a good price.
Basically there are way too many options to list them all. If you want to post your specific assembly, you will get more specific advice.
One note--conscientious builders avoid XPS because its blowing agents are potent, persistent global warming agents (aka carbon polluters). Long-term its stated value of R-5/inch drops to R-4.2 to 4.4, so there is not a strong reason to use it other than easy availability. Polyisocyanurate and denser grades of EPS are better choices in most situations.
Edit to add: I re-read your description of your assembly. Existing OSB sheathing is a good candidate for either Henry Blueskin VP100 or Siga Majrex SA self-adhered membranes. At least those would be my first choices.
Thank you for your help, Michael.
Tony