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Sealing joist end cavities.

2K views 6 replies 5 participants last post by  Newsman 
#1 ·
Well we had a home energy loss test and one of the big things found was the floor joist end cavities. They recommended foaming the areas to seal them the best. Is there any downside to doing this?? Also in a few places we have bays where the joists cantilever out over the sill. They are closed up, but not insulated. This makes for some cold floors!! Any downside to foaming these also? I will not be foaming in any wires or pipes or anything. Here is a shot of what I'm working with. Ceiling Room Architecture Plywood Wood
 
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#2 ·
You have to make sure your crawl space or basement is dry. I insulated those areas in my house and had to remove the insulation a few years later. Condensation formed due to the temperature change and got trapped in the insulation. There was lots of mold. Fortunately, no rot had started. After removing the insulation, I lined my whole crawl space with plastic and decided to pay higher heating bills. I still think that's the best way to go. I don't know if foam insulation would create less concern...I just used fiberglass insulation.
 
#4 ·
Air movements into a basement can easily reverse itself in the various seasons depending on your mechanical equipment. As the vapor barrier is installed on the warm side, heavily air conditioned spaces in the northern climates will generally condensate into the building envelope behind the vapor barrier in the summer, and a leaking air barrier will condensate during the winter in the envelope on the other side of the leaking vapor barrier.

Your best bet is filling the voids completely with a 3 lb foam, and also applying 6" of foam or so on the headers around the perimeter of the building on the sill/joist/header interface. One of the issues with foam is to apply when the relative humidity is low and make sure the building materials are dry, as you want a tight bond to avoid air currents moving thru the assembly.

One other item to ask your applicator is if the foam he is using is susceptible to ant attack. Have seen very serious attacks on foam by ants, such that one home was completely stripped of foam. This was about 5 years ago and I believe some formulations are now completely immune to this.

Fiberglass will leak air, foam is the best avenue.
 
#5 ·
We have a newer home with a full basement. The furnace is down there with 2 windows (closed) and air flow isn't a problem, nor is mold or smell of dampness. Around the perimeter of the sill plate has a spray of foam nothing on the bottom of the OSB flooring. My Father was also a home builder so I've seen this a few times.
One pic after my camera died but this is what the whole basement looks like.
Floor Wood Room Building insulation Flooring
 
#6 ·
We have a newer home with a full basement. The furnace is down there with 2 windows (closed) and air flow isn't a problem, nor is mold or smell of dampness. Around the perimeter of the sill plate has a spray of foam nothing on the bottom of the OSB flooring. My Father was also a home builder so I've seen this a few times.
One pic after my camera died but this is what the whole basement looks like.
View attachment 1869074

Yes, that's what I'm planning.
 
#7 ·
Paul, just saw this. Don't know how much area is involved or if you are thinking about cans from big box store or having someone do it for you. Just passing this listing along, distributor in New Paltz, (not all that far from you, and from what I have heard from couple folks, not a bad price. Might be worth a call, there number is on listing. You can ask them any questions you have. This is just an FYI and I have no connection to this. Just thinking it might be worth while since they have the slow rise cavity filling stuff.
MikeC
TIGER FOAM Insulation Kits - Surface Spray ASTM E-84
 
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