# Insulating Rim Joist - caulk or spray foam around edges?



## joecaption

Spray foam would be my choise.


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## Beepster

I believe that the word on the street is that you should caulk to prevent gaps from expansion and contraction. Did I use caulk when I did mine? No, I used expansion foam. So what. I got it to 99% perfect instead of 100% perfect. it is still a million times better than what it was.

B


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## markley

Thanks for the quick replies! I am guessing spray foam is easier as well?


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## ocd carpenter

Caulk is cheaper. If you have a big caulking gun, the big 850mL tubes of acoustical sealant end up being about half the price of the small ones for what you get, up here in Canada anyway. I just did mine and I used a combination of the caulk and foam, depending on the size of the gap.


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## SuperJETT

Great Stuff Pro would be my choice. It's what I've been using to do ours. Excellent control and no waste like the regular cans.


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## Windows on Wash

Either or will work just fine. 

Spray foam is usually easier.


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## Gary in WA

I'd caulk (allows slight movement) the wood joints at rim/joists and canned foam the f.b. perimeter, (except the bottom- use caulking there for movement) double air-sealed. The caulk/sealant would stop any air movement between joist cavities behind the foamboard. Fig. 2;  http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation/

Did you notice Fig.3- the adhesive on top the foamboard and the sealant/caulk on the bottom for movement. The rim joist, if solid wood rather than engineered wood, will move slightly with the seasonal changes; pp.51- chart (though that is for new wood and after first seasonal changes) after that changes will be less, depending on outside humidity.http://books.google.com/books?id=iw...um=3#v=onepage&q=cutting floor joists&f=false

The canned foam/f.b. will stop exfiltration of basement air getting to the rim surface but that is only 1/2 the solution. You need the caulking on the rim (behind the foamboard) to stop infiltration for a complete seal of air moving both ways. Otherwise the outside air could condense on the inside of rim, behind your air-sealed f.b. defense... smaller cells caulk pattern, in *BOLD*; http://joneakes.com/jons-fixit-database/743

Gary


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## HomeSealed

Good advice above... Spray foam will probably be a little pricier, but easier to work with. It can be really awkward to maneuver a caulk gun in that tight space.


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## hammerlane

*I had 162 lineal feet of rim joist done by a local spray foam company. Dont mind the dimensions on the chandelier. I was trying to sell it in that photo. *

*Before all I had was fiberglass stuffed in the rim joist cavities. After all sealed up with spray foam. *


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## drtbk4ever

Hammerlane, do you mind me asking how much that cost you?


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## hammerlane

drtbk4ever said:


> Hammerlane, do you mind me asking how much that cost you?


$800 for 162 lineal feet of rim joists in the basement and a 200 sq foot of wall space in an attic area above a garage.

Attached are a few photos:

A few photos below of the before and after of the area above my garage. 

After they did the spray foam in the attic area I fluffed up all existing batt insulation and laid new batts across the joists.


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## SuperJETT

That's a good price IMO. I have a friend who owns a spray foam company here that I've talked to several times about pricing and it's not as bad as it's made out to be on here. 

For our house, he gave a quick verbal quote of around $500 for the rim joist area though probably higher due to one section that's hard to get to and will take more time.


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## HomeSealed

That's a VERY good price. Around here, the going rate would be higher than that for the rim joist alone, without that attic wall.


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## hammerlane

Initial price was $1000. About a month later the compnay called me on a Tuesday night and said they had cancellation on Thursday morning and they would give me a $200 discount if I were to schedule in that slot. I took them up on it.


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