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Old 11-28-2011, 03:54 PM   #1
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rim-joist insulation - spray or sheet foam?


Ive got about 60 joist bays to fill in the basement of our 40yr old ranch. its clearly drafty, so id like to get this taken care of.

Option 1 is sheet foam, cut to fit the bays, caulked/spray foamed in place

Option 2 is spray handi-foam (or similar).

Obviously #2 is easier, but its also about $350 vs about $50 for #1.

Will I be able to achieve equal results w/ #1 if i take my time and caulk/spray foam all the cracks,etc or is it really worth the extra 300 bucks? For what its worth, ill be in the house for another 5-7 years.

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Old 11-28-2011, 08:40 PM   #2
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rim-joist insulation - spray or sheet foam?


Option 1, done properly/carefully, will work just as well.

What is your time worth? That is what it mostly comes down to.

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Old 01-12-2012, 05:02 PM   #3
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rim-joist insulation - spray or sheet foam?


I am currently doing this same thing and having trouble finding what type of foam board to use in the joist bays. EPS, EPS with film on each side, or XPS. I know XPS is recommended against basement walls. Also, the local big box stores in my area no longer seem to carry XPS.
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Old 01-12-2012, 05:11 PM   #4
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rim-joist insulation - spray or sheet foam?


Why not just stuff it with regular insulation with a barrier?

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Old 01-12-2012, 05:38 PM   #5
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rim-joist insulation - spray or sheet foam?


figured foam board with spray foam around the edges would give the best result (next to full spray foam). Just not sure what the best type of foam board would be.
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Old 01-12-2012, 06:48 PM   #6
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rim-joist insulation - spray or sheet foam?


I'd go with XPS and caulking. That foam board is not as open-cell as EPS to hold moisture leaking in from outside. Caulking would move with the rim joists (unless engineered wood) through the seasons; pp.51: http://books.google.com/books?id=iwS...rafter&f=false

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Old 01-12-2012, 06:57 PM   #7
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rim-joist insulation - spray or sheet foam?


Quote:
Originally Posted by redline9k View Post
Ive got about 60 joist bays to fill in the basement of our 40yr old ranch.
its clearly drafty
, so id like to get this taken care of.
Before you get to the joists... what's happening at the perimeter wall?
(gaps, cracks, ungasketed doors/windows, etc)

Quote:
Option 1 is sheet foam, cut to fit the bays, caulked/spray foamed in place
Option 2 is spray handi-foam (or similar).
fwiw... I'd hate to any spray in foam used in basement level floor joists.
well, at lest not without first doing a TON of plumbing and wiring work
and so forth to minimize the chance I'd EVER deed to dig in later and if so to minimize the number of spots that would be likely to happen.

hth
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Old 01-12-2012, 07:19 PM   #8
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rim-joist insulation - spray or sheet foam?


Definitely use the extruded foam board insulation. The foil facing can be used as a vapor retarder under certain circumstances. If this is a living space then you will need to cover the insulation with a fire retardant barrier such as 1/2 inch gypsum board.
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Old 01-12-2012, 08:04 PM   #9
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rim-joist insulation - spray or sheet foam?


Quote:
Originally Posted by TarheelTerp View Post
Before you get to the joists... what's happening at the perimeter wall?
(gaps, cracks, ungasketed doors/windows, etc)

fwiw... I'd hate to any spray in foam used in basement level floor joists.
well, at lest not without first doing a TON of plumbing and wiring work
and so forth to minimize the chance I'd EVER deed to dig in later and if so to minimize the number of spots that would be likely to happen.

hth
That would only apply if he was planning to foam the entire floor (every bay), which is not the case..


On the rim joist, for cost, XPS and foam or caulk is the way to go... but be WARNED, this is a total PITA. For my money ( and time), I'd buy a froth pack (two-part portable spray foam) to hit those sill boxes. By far easier, and probably more effective.
I'd also mention that I dont believe that XPS/foam or caulk can be done for $50.
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Old 01-12-2012, 08:08 PM   #10
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rim-joist insulation - spray or sheet foam?


I would (and did) use ROXUL to fill the cavities,virtually airtight,doesn't need a fireproofing cover (it is a fireblock).

And assuming cavities are at least 3 1/2 inches deep,you will get R-15 value insulation.
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Old 01-13-2012, 10:34 PM   #11
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rim-joist insulation - spray or sheet foam?


Either one is an air barrier (much more important than the insulating qualities), unlike fiberglass or Roxul (work fine behind the air seal). Fig. #2 here: http://www.buildingscience.com/docum...ce-insulation/

Check locally, it may be able to be left uncovered (though the smoke is toxic), depending on location and year of the code used; http://publicecodes.citation.com/ico...016_par015.htm

Some hints if you DIY: http://www.sprayfoam.com/npps/story.cfm?nppage=123

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Old 01-14-2012, 09:35 AM   #12
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rim-joist insulation - spray or sheet foam?


I am going to be a budinski for a second. Same topic different question. I am finishing of my basement in Minneapolis and plan on spraying the rim joists. 12" block, 10" joists, rim joists partially backfilled with concrete at build (1957).

My question is: do you foam spray to fill the entire rim joist cavity out to the framed basement wall (1" XPS board on wall) or do you just spray a 1-2" layer covering all surfaces?

B
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Old 01-14-2012, 09:37 AM   #13
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rim-joist insulation - spray or sheet foam?


I am going to be a budinski for a second. Same topic different question. I am finishing of my basement in Minneapolis and plan on spraying the rim joists. 12" block, 10" joists, rim joists partially backfilled with concrete at build (1957).


My question is: do you foam spray to fill the entire rim joist cavity out to the framed basement wall (1" XPS board on wall) or do you just spray a 1-2" layer covering all surfaces?


B
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Old 01-15-2012, 08:39 AM   #14
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rim-joist insulation - spray or sheet foam?


Quote:
Originally Posted by titanoman View Post
Why not just stuff it with regular insulation with a barrier?

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Because any profession with building science knowledge will know that this will only trap moisture making the fiberglass ineffective and for mold to grow. Rim joists need to be air sealed and insulated to the same R-value your local codes require for the exterior walls. R19 in my area. Here is how I do rim joists http://www.homedoctorofamerica.com/rim-joists.

Your first solution (flash an batt works fine. Easy to use Roxul batt and spray foam. Or use polyicocyanurate foam board. Spray foam is much easier and is the only method I use.
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Old 01-15-2012, 08:40 AM   #15
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rim-joist insulation - spray or sheet foam?


Quote:
Originally Posted by Beepster View Post
I am going to be a budinski for a second. Same topic different question. I am finishing of my basement in Minneapolis and plan on spraying the rim joists. 12" block, 10" joists, rim joists partially backfilled with concrete at build (1957).


My question is: do you foam spray to fill the entire rim joist cavity out to the framed basement wall (1" XPS board on wall) or do you just spray a 1-2" layer covering all surfaces?


B
In your area use closed cell foam 3" thick

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