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Old 02-07-2010, 01:55 AM   #1
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Rim joist insulation


My house is 6 years old and located in Nebraska. In the basement, in the rim joist area, the builder installed batt insulation with the faced side toward the outside or against the wood. I was going to install some more insulation in the area but this is what I found. I remove some pieces that the builder had installed and found the wood and the vapor barrier was damp on the lower horizontal and outer vertical surfaces. What can I use to insulate this area to avoid moisture showing up again? XPS? If XPS then where should it be installed? The pictures I have attached show the area I'm dealing with. The pictures with the insulation installed is how the builder put it in.

Thanks, Mark
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Old 02-07-2010, 07:42 AM   #2
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batt insulation is this area is incorrect. Best to use spray foam. It will create a complete air barrier while still allowing moisture to travel freely in both directions as needed. Rigid foam is another acceptable approach but must be done very tightly with all seams sealed with spray foam. remove the old batt insulation first.

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Old 02-07-2010, 07:52 AM   #3
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Bob, Not to question your wisdom, or hijack the post but I was of the impression (2lb) spray foam creates an air tight vapor barrier, until I read your comments about moisture traveling both directions.
I am in a zone colder or as cold as Mark and debating about spray foam, versus rigid HD foam on my inside basement walls and some rim joist around my slab porch with cold room below. Can you proivide more details on foam?
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Old 02-07-2010, 07:55 AM   #4
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There are 2 types of foam, one with almost perfect sealing ability and one with less...open versus closed cell foam. Also one expands alot more than the other.
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Old 02-07-2010, 07:58 AM   #5
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Morning CC , Yes 2lb as referenced versus 1/2 lb. Thats what I 'm trying to get Bob to expand on...pardon the pun
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Old 02-07-2010, 09:03 AM   #6
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hey chemist!....are you in fact a 'chemist'? Love the stuff.
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Old 02-07-2010, 09:31 AM   #7
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Quote:
In the basement, in the rim joist area, the builder installed batt insulation with the faced side toward the outside or against the wood.

Thanks, Mark
Paper/vapor barrier should have been on the warm side. It was installed incorrectly which caused the moisture.Alos in your first pic. The batt insulation is laying horizontal and should have been vertical. In any case, closed cell spray foam is best. I am also about to do this in my home. I think I am going use the 2" extruded polystyrene, caulk and spray foam to seal gaps.

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Old 02-07-2010, 09:38 AM   #8
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When you say "spray foam" are you talking about the kind of spray foam you spray in and it expands to competely fill in the area? Is this something I could buy at a home improvement center? If so, what do I need to ask for?

If I go the rigid board way, once I place the rigid against the outer surfaces on the inside of the rim joist, do I still need to install batt insulation to fill the rest of the area? Some of my rim joist areas are about 2 feet deep. Do I put the rigid board on the outer vertical and lower horizontal areas? Like creating an L shape inside the area.

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Old 02-07-2010, 10:25 AM   #9
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Mark,
Smoke from foam can be toxic so our codes here require that it be covered with fire proofing such as drywall. I insulated the rim to R33.
In my case I sealed the sole plate top and bottom at concrete then the rim joist, each joist bay top bottom and sides and came out 8" from the wall with a foam gun with needle tip, the around all windows, then tucked R33 batts into the bays, rather than fully foam.
Cost for 1000 square ft basement, approx 160 ft of rim was about $130 in R22 batts plus a couple of cartridges for my foam gun. My energy auditor rated my sealing work as superior to ANY of 300+ homes he has tested, foam sprayed or otherwise and he was blown away by the air loss blower door test results. My change in air loss was substantial after doing the rim and under my baseboards that I have surpassed new building code He said if I continue I may need to consider an HRV...0ver 50 % reduction in air change.. House is far less drafty, 35 years old
I have yet to do any exterior work or insulate the basement walls.

However, I chose to increase by R22 in addition to my old batts properly cut ant tucked because I have aluminium wiring and want to have future access.

I am still interested in Bob`s experience and comments about foam in all areas , rim joist or other. Bob is a pro and he uses this stuff...

CC, I`m not a Chemist just my nickname, I use a lot of homeopathics and herbal remedies and recommend them to friends so I got tagged with a nickname...
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Old 02-07-2010, 01:00 PM   #10
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chemist- is there any way you can provide pictures of what your process was? I cannot mentally see what coming out 8" did for your joist area. I am a visual type of guy, pictures would be greatly appreciated.
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Old 02-07-2010, 01:58 PM   #11
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I haven't seen a good solution published yet for this problem, I'm attempting to find one for my own basement, and will share when I do.

The problem is this: if you seal it (from water vapor going through, that is), you run the risk of water collecting on one side or the other, and the growth of mold growing on wood, dirt, etc.

Vapor barriers in basements in general are very dangerous mold problems.

My first cut is to use Tyvek to seal against air intrusion, then EPS. Once you've stopped air, the seal around the EPS doesn't need to be perfect. The Tyvek will allow the end of the bays (rim joist) to breath water vapor in either direction.

Jonathan
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Old 02-07-2010, 01:59 PM   #12
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Quote:
Originally Posted by Chemist1961 View Post
Bob, Not to question your wisdom, or hijack the post but I was of the impression (2lb) spray foam creates an air tight vapor barrier, until I read your comments about moisture traveling both directions.
I am in a zone colder or as cold as Mark and debating about spray foam, versus rigid HD foam on my inside basement walls and some rim joist around my slab porch with cold room below. Can you provide more details on foam?
moisture travels in many ways not only with air movement. We need to control air and moisture in different ways. A basement wall needs to dry to the inside below grade and to the outside above grade. The rigid foam still allows moisture to escape from the moisture in the concrete or block foundation into the void between the insulation and the wall.

The foam board is used warm the exterior wall enough to prevent condensation. The perm value is not 0 and as such does not prevent water moving by diffusion but does stop water movement by capillary action. This is why it is needed below the sill plate also.
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Old 02-07-2010, 02:02 PM   #13
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Quote:
Originally Posted by joncampbell View Post
I haven't seen a good solution published yet for this problem, I'm attempting to find one for my own basement, and will share when I do.

The problem is this: if you seal it (from water vapor going through, that is), you run the risk of water collecting on one side or the other, and the growth of mold growing on wood, dirt, etc.

Vapor barriers in basements in general are very dangerous mold problems.

My first cut is to use Tyvek to seal against air intrusion, then EPS. Once you've stopped air, the seal around the EPS doesn't need to be perfect. The Tyvek will allow the end of the bays (rim joist) to breath water vapor in either direction.

Jonathan
there is no need for tyvek on the basement wall. No air movement to block. But you are not blocking moisture traveling through the wall cavity to escape to the exterior. Then the water will condense on a cold wall. this is why you need at least 2" foam on the wall in colder climates.
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Old 02-07-2010, 02:06 PM   #14
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Does a can of Great Stuff have enough pressure to "spray" out if somehow a smaller tip were placed onto the nozzle? I have been looking into the spray foam, found 100bf on ebay for a decent price but even that decent price is a whole lot more than some rigid foam and some caulk. There are a couple joist that at a later time I would love to access to be able to replace/run new wire and the spray foam might make that a problem. Well I'm starting to ramble..sorry.
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Old 02-07-2010, 02:26 PM   #15
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another way to approach this is the "hybrid" method. Use a can of spray foam (hilti no great stuff) to seal all edges along the outside and top. Then use Roxul insulation batts. This is not effected by moisture.

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