Sealing the break between multiple sill plates
Simple question, hopefully simple answer…
I am using the epdm gasket from conservation technologies to seal a bottom plate to a concrete stem wall. My plates will not run the entire length of the wall, however. So my question is: what should be done to ensure a good seal where the plates butt?
(I ask this sort of assuming that the gaskets would need to butt into each other, as they typically seem to be stapled to the bottom of the plates, and so could not be continuous… however I realize I probably could forgo stapling them to the plate and run the gasket continuous, save for the corners. I would then presumably just caulk the wood joint in the actual plate.)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I expect that Conservation Technologies would have another gasket for that joint. Or maybe tape (completely around the plate ends). I have low confidence in caulk. Or in acoustic sealant being misused as caulk.
Tyler,
I'm not aware of a product specifically for the butt joints between plates, but many builders use Tremco acoustical sealant there. Check out this mudsill assembly:
https://www.greenbuildingadvisor.com/article/air-sealed-mudsill-assembly
Or try the video:
https://www.greenbuildingadvisor.com/article/part-2-of-gbas-video-series-on-a-passive-house-project
Thanks Brian. Looks like they do just caulk/seal the butt joint.
I've got a somewhat unconventional thing going on in this area and I started wondering if I could do something like what I drew out below.
Its an 8" wide stem wall with a 10" wide double stud wall going on top. So the plan is 3/4 inch pt ply below the 2x6 sill plate (will be glued/caulked together).
Its cold out here now in Maine, and so i'm not too confident in caulks, tapes, and the like. I actually already have enough 3 inch gasket to do two wide, and I was planning on putting both under the pt ply, but I would love to kill two birds and also get a seal on the bottom of the sheathing while I'm at it.
Anything wrong with trying this unconventional seal arrangement?
I caulk the joints after the plates are bolted down, Ive bed the joints in sealant as the plates are going in and then caulked the top and sides as well but I think thats a wasted effort. I caulk all seams, corners and bottom edge of floor system inside and out as that is being installed prior to floor sheathing, otherwise you cant get at it effectively or quickly.
Later on the box sills get spray foamed covering all these joints and we make sure the entire sill plate is covered as well as the top edge of the poured wall. Makes the whole thing very tight, Ive done it this way for quite awhile now and blower door/infra test these out. I use a cheap 3006 sealant which is a class 35 sealant, always over basic foam sill seal which works much better than people give credit for (I think a lot of naysayers are armchairing theory or selling rather than actually building houses and testing).
As far as caulk and airtightness, yes at some point it will debond leaving a microcrack, think of it as a flexible filler reducing your ELA. Under failure tapes do not reduce the original ELA, they simply cover it, so in event of a failure you are back to where you were in the first place.
Im not saying tapes are garbage, some of the tapes Ive tried seem great from initial adhesion, but from a cost/benefit and long term performance standpoint I would rather fill then cover if I had to pick one.