Air sealing with 1/4in open cell spray foam
I know it’s not closed cell, i know its not 2in minimum, but if i spray a mist with a wide spray nozzle and standard door and window foam to seal my space between floors joists, then i have cheap fiberglass R20…
What type of air sealing can i expect?
This is a last second low cost improvement i’m looking to do and elaborate taping vapor barrier will be too leaky, i could always cut out some foil faced insulation and spray the gap with the door and window foam but i dont really have time…(i have done in the past)
Quick and cheap i figured that a 1/4-3/8 thick mist of spray foam would still give me adequate-ish air sealing. any thoughts? building is 100 years old, will be a rental property, it will be much better than before regardless but i still want a minimum of comfort/reasonable electric bills (climate zone 6)
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Check manufacturer’s specs. They will give the thickness needed for an air barrier. Typically 1” for closed cell and 3.5” for open cell.
I would check out https://aeroseal.com/aerobarrier/
Aeroseal is super expensive and is a whole building solution, I’m familiar with the product and would be great if i wanted a super tight building, but I’m just aiming for minimal improvement in the rim joist area
1/4" isn't really going to do it, and you're likely to have gaps and voids randomly throughout. You're probably better off targeting your air sealing: it makes no sense to apply spray foam to the side of a joist, for example, since the solid wood board is already an air barrier. Where you need to concentrate your air sealing efforts is gaps and cracks (which is why they make "gaps and cracks" great stuff :-). Canned foam works pretty well with larger gaps of 1/4"+, but smaller ones are usually easier to reliably seal using caulk. Sometimes you can use the plastic tips for the great stuff pro gun to get into smaller gaps down to around 1/8" though, and I HIGHLY recommend the gun if you're doing any kind of larger project with canned foam.
Bill
Agreed side of board is pointless for air, my issue is its and old structure that is what we locally call board on board, basically full 2 1/2 thick wood planks one above each other with the occasional vertical member and a dovetail joint every 10 planks or so, the joists are inset into this structure. I could concentrate on caulking the joints with acoustic/vapour sealant, but some boards i wont have access to properly caulk (fit the gun at the right angle). I dont need a full air barrier, just remove the drafts. Air infiltration at negative pressure like a blower door test doesnt bother me too much. I understand I’ll never meet manufacturer specs, I’m looking for a half *ssed solution with semi-reasonable result.
what i mean to use is a the nozzle in the video below to wide spray door and window foam
https://www.youtube.com/watch?v=IXBa838-LJM&ab_channel=AdfastCorp
here is another european model:
https://www.youtube.com/watch?v=IXBa838-LJM&ab_channel=PenosilOfficial
again, i know its cutting corners, i just figure it still has a value and am hoping one of the energy nerds on this site will agree with me that its not useless!