Inconsistent air-sealing plan
blamus20
| Posted in Green Building Techniques on
Is it common to have the exterior sheathing to be the airtight layer, and then transition to an air tight drywall ceiling? So the air sealing plain goes from outside the insulation to inside the insulation. Is it just a matter of sealing the drywall to the top plate to make this work?
I have to air seal the ceiling instead of the roof because its going to be a vented attic, with insulation piled on top of the ceiling.
Climate zone 5 in CO.
Is there a better way to do it without adding cost and complexity?
And then how do people air seal a cantilevering floor deck?
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Replies
Here's an article about one way to do it: https://www.finehomebuilding.com/2014/03/05/a-practical-air-sealing-sequence
Bernard,
Brendan gave you the best link.
Here's another link, however, to a photo-rich article on a project that used the same cantilevered-plywood-top plate approach discussed in Brendan's link: "Building a Passive House for $163 per Square Foot."
Thank you thats what I needed!
I also found a slightly different detail (post 12):
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/19744/airtight-drywall-anyone
There it shows a detail without the cap on top of the top plates, and no need for 1x4 furring between the ceiling drywall and the trusses. Is there an advantage to do it one way or the other?
Bernard,
1x4 strapping is not necessary. In the Northeast of the U.S., drywall contractors like ceiling strapping. In other areas of the country, they don't use ceiling strapping. Different traditions, but either way works.
The key is to extend the air barrier from the exterior ceiling to the drywall in a way that ensures a long-term seal. I think a wide plywood top plate that cantilevers to the interior works well. If you aren't using strapping, you can use 1/2-inch plywood for the cantilevered plate, and tape the seam with drywall compound and paper tape.
Or you can use a variety of approaches that use goo, mastic, caulk, or tape. As long as you've thought your detail through, and you feel comfortable with the tightness the detail achieves, you're good to go.
concerning air sealing the lighting, Whats the easiest form of lighting to air seal. Recessed cans seem like a lot of effort having to build foam boxes etc. Track lighting?
Lots of companies sell airtight electrical boxes. Allied Molded calls their airtight boxes "Vapor Seal" boxes. Here's a link:
Allied Molded 4-inch-round airtight electrical box
Surface mount LEDs can give you a recessed can look with a better seal. I am using Eaton's Halo ones that I got from Home Depot.
Bernard,
The vast majority of lights are designed to be mounted to a standard round box and take the same effort to air-seal as, no matter what the type, you are really only sealing the box.