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Any Way to Insulate Between Very Close Joists?


Yukon Youngun's Avatar
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01-16-16, 07:51 AM   #1  
Any Way to Insulate Between Very Close Joists?

I want to insulate the joist area shown in the first photo. The second photo shows the back side of the same joist, the foam plug I stuck in a while back for an air block and the cut end of the actual end joist to the right. This wall is about 12 feet long. Can I, or should I, insulate the gap between the two joists where my plug is or just the inside?



 
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Bud9051's Avatar
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01-16-16, 08:44 AM   #2  
I'm not sure where that gap fits into the total framing, it goes from where to where? But gently stuffing any insulation in there as far as you can reasonably get and then air sealing the exposed gap should be just fine.

Bud

 
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01-16-16, 08:45 AM   #3  
Having trouble relating the two photos and understanding where this is in the structure.

But in general, you want to air seal and insulate anywhere there is a boundary between conditioned and unconditioned space. Conditioned space is heated and/or cooled. Unconditioned is not.

So if you have outside air on one side of the area you show in picture 2 and inside air on the other side, then yes, you want to air seal and insulate the area.

Hope this helps.

 
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01-16-16, 11:09 AM   #4  
The 6" wide strip of drywall runs the length of the exterior wall in question. Notice the joist immediately above is set just over 1" back from the front edge of the dbl top plate. Since this is 2x6 framing, this particular joist is the second at this end of the room. Behind this joist is the gap having the foam plug at the end only, then the outside/end joist shown as end grain. Essentially, the gap is a typical joist space but at the end of a room that is short of a 16" center. Note, the second pic is taken inside that dark triangular opening at mid right of the 2nd pic.

The only way I can imagine to insulate down the full length of the wall in that gap is with a very long spray foam nozzle, which I suspect is nearly impossible. But, would it suffice to put up sheet foam on the inside joist? I'm not sure what that might mean for air/vapor sealing...

 
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01-16-16, 11:37 AM   #5  
OK, I think I've got it. You have two joists an inch, inch and a half apart, both sitting on top of double 2x6 top plate and you really only have access to one end of the opening between the two.

What's above, the second floor?

My suggestion would be to air seal the open end as best you can (your plug is fine if you caulked it), Put a strip of rigid foam along the inside joist, and forget about it.

I suppose you could drill a 1 1/2 hole at the far end of the inside joist, cover the open end with mesh, and try to blow cellulose in there. You might have to drill more than one. Or drill a bunch of smaller holes in the joist and fill the space with foam. Or slide in a long piece of rigid foam and call it good enough.

Sure would been nice of the builder to have dealt with this before it got covered up.

 
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