foam insulation


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Old 12-15-20, 09:16 AM
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foam insulation

Hello everybody,
New to this site and probably should have joined sooner. Got a question for all you diy'ers like me, I have an old house built back in the 20's and finally getting around to insulate my cold basement. My plan is to start with 2"x4'x8' polystyrene sheets and cut 7 1/2" x 14 1/2" pieces to push up to the outermost edge of the sill plate, against the end joist. Then I'll seal up any imperfections with spray foam or caulk. Undecided on this. Any who, on the other 2 sides of the house, the end joists run parallel with the floor joists and what they did was put a joist an 1 1/2" from the innermost edge of the sill plate. At first, I planned on nailing a 7 1/2" x 27' (27' is width of house) strip against the floor joist, leaving 1/2" hanging over the block basement wall, thus leaving a gap that's not insulated. I thought I read somewhere that's not a good idea because it makes the wall cold and will cause problems with windows above it. I do have a big picture window (4 1/2' x 8') right there on the first floor. Haven't had any problems with the window frosting up (replaced 2 yrs. ago) so far, but that end of the living room is usually cooler. My intentions with this situation was to drill 1/2" holes (or bigger) 12" apart, horizontally down the center of this floor joist and shoot foam in it. I'm afraid doing this blind like that may leave voids unfilled. What do you guys think? I'm open to any and all suggestions and look forward to your advice.

Thanks, Mike
 
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Old 12-15-20, 09:32 AM
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You would probably be better off filling a gap like that with cellulose or blown fiberglass. You staple a fabric across the gap, then cut an X in it every so often so you can insert the hose and blow it full.

Its too big of a gap for any kind of diy foam.
 
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Old 12-15-20, 05:16 PM
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foam insulation

Thanks for the ideas xsleeper, only problem is, I would still have to drill holes in the innermost floor joist, no matter what I use to insulate. Its completely boxed in. Mike
 
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Old 12-15-20, 05:20 PM
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what they did was put a joist an 1 1/2" from the innermost edge of the sill plate
This makes it sound like there is a 1 1/2" gap. Depending on what the siding is, you can remove it, drill holes and blow it in through the rim joist.
 
 

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