Belt & suspenders for sill plate
tjones1014
| Posted in General Questions on
Our sill plate is taped on the exterior to the foundation with Siga Fentrim. We want to have a belt and suspenders approach with it, so we also caulked on the interior where the plate meets the slab.
I got to thinking yesterday about the stud bays. Is it best to also caulk the bottom of each stud bay where the sill plate meets the OSB? If there is any gap between the plate and the OSB, it seems like air could still come in if the Fentrim ever fails.
Is this worth doing, or is it overkill?
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Bubbling this back up. I've attached a picture of what I'm referring to. Should we caulk where the red lines are? Or is the slab to sill plate caulking enough?
We found one section where the Fentrim isn't adhering well to the foundation because the guys who did it rushed through and taped over leaves and such. So we want to be sure we have the full belt and suspenders approach nailed down.
I think you would see diminishing returns here. For that much caulk and sealant at each bay the amount of airtightness you'd gain would probably be pretty minimal.
If your sill plate has an EPDM gasket or a sill sealer with caulk at either side and the bottom of your OSB is taped also, you already have (2) more instances of airsealing.
I also liked the response of going over the Fentrim with liquid flashing that @cs55 suggested if you want to tackle that first before springing for major caulking on the inside of the stud bays.
This is a reno on a 2001 home, so no EPDM gaskets or sill sealers underneath the sill plate. I think we should be able to reach the bottom portion of the Fentrim tape. The exterior cladding is already up, so it may be tricky in areas.
im not gonna google it but see if that tape is compatible with liquid flashing
its typically fine to apply liquid flashing over tape, but not tape over liquid flashing. sometimes the tape needs to be cleaned with acetone to ensure the liquid will adhere.
Thanks, I'll look into that. In the event that it isn't compatible with liquid flashing, or if we want to be extra sure about the belt & suspenders approach, are the areas marked in red where the caulk should be applied? Or is it only where the slab meets the sill plate?
https://i.imgur.com/3aEwZzO.png
air moves in every direction that it can and will go through the tiniest cracks.
since you can't get caulking between the sheathing and the framing near the bottom plate, then any potential air will move between the sheathing and back of the 2x4, then out where your red line stops.
if those red vertical lines went from your bottom plate to the top plate and for every stud bay, then that should work great. which would be a lot of effort and money depending on the size of house.
i'm not smart enough to comment on the efficacy of sealing up what you marked off compared to nothing at all or fully committing to sealing each stud bay from the interior.
Good point! That would be a lot to have to do every stud bay, so I don't think we will go that route. We had someone suggest doing the same sort of outline in the tops of the stud bays since we weren't able to tape the top plate from the exterior (the way our roof framing was constructed back in 2001 made it difficult to reach). I'm now wondering how effective it will really be
if your top plate to sheathing isnt taped, maybe the every stud bay route would be more enticing, even if it might take better part of a day to knock out
you might check out a habitat for humanity store if you have one nearby. i know they are not all identical but the few ive been to have always had pallets of caulking for $3 each. the one near me has killz high performance -- just a generic modified polymer sealant. terrible to work with but obnoxiously sticky, stays softish, pretty flexible. cant be beat for $3 a tube. ive gone through dozens of tubes for interior air sealing in locations i dont care about looking good 😅
https://www.homedepot.com/p/OSI-SC175-28-oz-White-Acrylic-Latex-Draft-and-Acoustical-Sound-Caulk-Sealant-12-Pack-1496542/202768260
this post moderation queue is obnoxious
something like that would also be pretty inexpensive, you just need to buy a 29 oz caulk gun. be sure to get a gun that has a high ratio so you dont burn out your forearms 😅 or use it as an excuse to buy an electric gun
i think a lot of people on here really like accoustical caulking for airsealing.
For the top plate, I've noticed that I can reach short sections where the OSB meets the top plate in between the roof rafters all around the house. Is it worth it to use the extra tape I have to seal these sections? I've already caulked the top portion inside the stud bays as previously suggested