Vaulted ceiling air barrier
I’m having the shell of a house built for dear old Mom, and have to stay within the building program of the contractor until everything is dried in.
The main area is vaulted with scissor trusses and I saw how Hammer and Hand in Portland placed a strip of plywood on top of the top plates, sheathed the ceiling in OSB and taped the seams for an air barrier.
I need an air barrier on the vault before drywall because I will have very little access to air seal and blow insulation with all the drywall in place. An OSB ceiling allows me to leave access until the last piece goes in. I’ll be blowing insulation as I crawl out of the last hole. (It’s just my time).
Anyhow, as Hammer and Hand shows in their Passive House video (https://youtu.be/ACDZ3gT7M4Q?list=PLbEMl6WikrRXrPEOYFK1e3SkKZ4IKeahb), the OSB flange extends 3/4″ into the room. Could this be some type of membrane, taped to the exterior sheathing AND the ceiling OSB? If so, this would solve having to run the flange around ALL the plates, even where there won’t be an OSB ceiling.
Thx.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Mark,
Yes, you can use a membrane as your air barrier, as long as it it tough enough to handle job-site abuse, free of holes, durable, and easy to tape. You can use a strip of membrane in this location, and leave a visible flap for later taping.
Candidates include leftover materials -- for example, housewrap. Just make sure that the material is tough and hasn't been damaged.
-- Martin Holladay
Thanks for the good word, Martin.
I'll also be using TimberLok or Simpson SDWC screws in place of hurricane clips to make a cleaner connection.
Martin,
For all the rooms without the vaulted ceiling and OSB, I want to use the ceiling drywall as the air barrier (but sealing the seam from above at the rake probably won't happen).
Combining a membrane over the top plate and cross hatching (for more cellulose), would what I have pictured work well? The red is the membrane and is shown oversized for clarity.
What would be better for sealing the slot? Spray foam or caulk? What would be resilient as the 2x2 shrinks?
Mark,
Is the blue panel OSB or drywall?
Can you be more specific about what you mean by "cross-hatching"? What and where is the cross hatching?
If you leave enough of the red membrane dangling, you can tape the red membrane to the blue panel (the OSB or drywall), as long as you intend to install wood trim that will hide the tape.
-- Martin Holladay
Martin,
The blue panel is drywall. I made it transparent for illustrative purposes.
I could refer to the cross-hatching as a Mooney wall, but Riversong might take exception to the name (https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/19585/comparing-thermal-bridging-between-envelopes). I didn't yet draw in the cross-hatching every 24" down the wall.
I wasn't planning on any crown moulding and didn't think tape on the face (or back) of the drywall would last. Pro Clima does have their Contiga PV - fleece tape for wood to plaster connections for $1/ft but then I'd be asking the drywallers to learn a new trick.
I'm thinking sprayfoam in the gap would complete the continuity at the ext wall and would be occupant-proof. I can spray the foam before the drywallers start hanging the walls without interrupting their work-flow.
Mark,
Taped drywall is a durable air barrier. If ordinary paper drywall tape (stuck in a bit of drywall mud) is durable -- and it is -- then I don't know why housewrap tape or a fancy European tape stuck to drywall wouldn't be durable, too.
-- Martin Holladay
Thanks Martin.