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markley 01-11-2013 02:23 PM

Insulating Rim Joist - caulk or spray foam around edges?
I am getting ready to insulate the rim joists in my unfinished basement and am intending on using 2" XPS and sealing around edges with either caulk or spray foam (Great Stuff). Is one better than the other? easier? more cost efficient?

If using caulk, is there a certain type that I should use?


joecaption 01-11-2013 02:30 PM

Spray foam would be my choise.

Beepster 01-11-2013 02:30 PM

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.


markley 01-11-2013 02:32 PM

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

ocd carpenter 01-11-2013 02:38 PM

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.

SuperJETT 01-11-2013 06:04 PM

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.

Windows on Wash 01-11-2013 08:20 PM

Either or will work just fine.

Spray foam is usually easier.

Gary in WA 01-12-2013 02:50 PM

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;

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.

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;


HomeSealed 01-15-2013 08:58 AM

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.

hammerlane 01-15-2013 09:26 AM

1 Attachment(s)
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.

drtbk4ever 01-15-2013 09:29 AM

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

hammerlane 01-15-2013 11:36 AM

3 Attachment(s)

Originally Posted by drtbk4ever (Post 1093959)
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.

SuperJETT 01-15-2013 12:08 PM

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.

HomeSealed 01-15-2013 12:11 PM

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.

hammerlane 01-15-2013 12:41 PM

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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