How to Hang Airtight Drywall
I was watching the GBA/FHB video “How to Hang Airtight Drywall on Ceilings”…
http://www.finehomebuilding.com/how-to/video/hang-airtight-drywall-on-ceilings.aspx?ac=f
and boy howdy .. they sure used a lot of “gooey stuff”…
I understand how the adhesive on the rafters may add to racking strength and may help avoid fastener pops.
However, I don’t understand how the adhesive (on EVERY rafter) contributes to the air barrier???
It seems to me that they are putting a lot of gooey stuff in places where it is not necessary (as part of an air barrier)…
In this BSC Airtight Drywall Approach PDF
http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/files/bscinfo_401_airtight_drywall_approach.pdf
…Notice that they do not put gooey stuff on EVERY stud….instead the gooey stuff goes at the perimeter of the drywall and where the drywall “changes plane” NOT in the “field” of the drywall.
Why does Myron need to put Gooey stuff on every Rafter?
It also looks to me like they may be missing “backer” and Gooey stuff in other places where it is more important.
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Replies
John,
Jeremy Spencer raised the same question you did a few days ago; he posted his question here:
https://www.greenbuildingadvisor.com/green-basics/video-how-hang-airtight-drywall-3-3
Jeremy asked, "I don't quite why all the internal caulking to each stud is required. I can understand perimeter caulking, but once the joins in the drywall are taped and coated it forms a continuous air barrier, so don't you just need to focus on edges and penetrations?"
Here's what I wrote in response to Jeremy Spencer:
You are correct. I agree with your suggested method, which complies with the traditional interpretation of the Airtight Drywall Approach.
I think that Myron Ferguson's caulk-heavy method has more to do with a desire to adhere the drywall to the studs than any need for air sealing.
If you want to read more about the traditional methods used for the Airtight Drywall Approach, you can check out my article on the topic, Airtight Drywall. In that article, I describe some of the locations that need sealing:
"• Drywall perimeter. Use a continuous bead of caulk or drywall gaskets along the bottom plates and top plates of exterior walls, along the top plates of partition walls under insulated ceilings, and around the perimeter of all rough openings.
"• Intersecting walls. On partition walls that intersect exterior walls, seal both sides of the stud nearest the intersection. With caulk, seal the crack between the first stud in a partition wall and the partition’s bottom plate and top plate.
"• Windows and doors. Seal between window frames and window rough openings using low-expanding foam, gaskets, or backer rod and caulk. If your windows have drywall returns, install gaskets on the faces of the rough-opening studs (behind the drywall jamb extension) rather than the edges of the stud. Caulk window and door casings to the drywall."
I agree w/ Martin, and I would also recommend the use of gaskets over goo. Conservation Resources p-gasket is a nice one. It allows you to install all the gasket before hanging any drywall, and you don't have to worry about forgetting a spot. It's especially valuable if you're hiring out the drywall - I don't know any drywallers other than Myron who are paying much attention to the topic. Better to have your quality control be independent of the hanging.
Martin,
I'm curious why sealing the vertical drywall edges at the intersection of two exterior walls isn't also recommended. Or am I interpreting your reply above incorrectly?
Matthew,
I wrote, "On partition walls that intersect exterior walls, seal both sides of the stud nearest the intersection." Along with normal drywall taping, that should address any potential air leaks in this area.
What about where two exterior walls meet? Does the corner framing act as a good air barrier?
Matthew,
Air leakage at that intersection is handled by ordinary paper drywall tape.
Airtight Drywall on a truss ceiling: For an over-garage apartment, the roof trusses span 24'. The engineer has specified that partition framing end 1" shy of the trusses (held with clips) and that drywall fasteners be kept back 18" from the wall-ceiling joint, all to allow for flexing.
Any thoughts on how to assure this joint is airtight? Maybe rock the entire ceiling above the partition framing, then build the wall with the gap, and finally finish the seam with a sliding or flexible molding?
Thanks!
Curtis, I would install the board exactly as the engineer has speced it. The air barrier will be the tape, joint compound and painted surface. Be sure to gasket the top plates of the interior partitions and seal any holes for services.
Edit: While the clips and fastener locations are pretty standard, this is the first time I've seen lowered interior partitions speced. I imagine that the idea behind this is to insure the interior partitions don't become load bearing, but with trusses uplift is the problem, the bottom cord doesn't deform downwards. Lowering the top plates means they can not be lapped at the exterior walls and may mean you have to individually cut all interior studs. Not a big deal, but probably not really necessary. I'd ask the engineer to think that one over again.
Relying on conventional paper tape and mud is not the road to airtightness. Those joints will leak even if they look sealed. That is for sure; and if interior partitions are not load-bearing, why not install the exterior wall and ceiling drywall before framing them .
Drywall gaskets stand off the drywall and do not make for good shear strength; drywall sealant or adhesive do allow a tight fit for structural considerations; they also seal the drywall screw penetrations.
For all the analysis and good design and materials talked about on this site, going with conventional drywall methods is ignoring the elephant in the room.
If you look at website 475, referenced on GBA several times, you will find air-sealing tapes that span drywall joints and drywall-frame connections. These tapes are designed so they can be under layed the finishing drywall joint tape and mud. These tapes flex and seal.
Instead of conventional drywall tape and mud, to handle perimeter flexing, Trim-Tex or No-coat seem a no brainer. Conventional mudding and corners are passé if air sealing matters since drywall is not airtight if the building moves. Wooden buildings move.
Folks don’t like the “breathing” analogy for buildings but even so, they do flex … drywall joints and mud, being rigid (no ductility) are the weakest link to air sealing.
Frankly, its time to throughout drywall, gypsum board, sheet rock, -- whatever name it goes by -- and find a better material for building the interior envelope. Drywall, fiberglass and asphalt are the trinity of the most ridiculous material properties one could think of in this day and age.