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Better to cut batts than scrunch them to open up space at rim joist?

Better to cut batts than scrunch them to open up space at rim joist?

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  #1  
Old 08-21-11, 02:42 PM
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Better to cut batts than scrunch them to open up space at rim joist?

Note the first two background paragraphs on this post is the same as a different post, but it is a different question.

Background
We're re-insulating our rim joist. We decided to cut pink 2" XPS R-10 into blocks for each area, and are actually glueing two pieces back to back to give 4", giving up to R-20. (Bit more work, and we only needed to spend an extra $28 on another sheet of XPS, so why not.) We're leaving room around all sides, using a bit of glue to get it to stick to the rim joist, then filling all 4 sides with Great Stuff. Even though it's a lot more work, we decided to do it this way because it will save a few hundred dollars over the spray foams traditionally used.

The basement is finished with a drop ceiling, and we can easily access the rim joist on the front and back of the house. It appears they did a decent job on the basement walls when finishing. They used a few inches of fiberglass batt's against the concrete walls, made a frame, and drywalled it. Unfortunately, this means we can't get to the rim joist on the sides -- only to the joist next to the rim joist.

Question

There are a few areas on the sides where we can get to the actual rim joist. Perhaps the other piece of wood I speak of isn't actually a joist... Because it's not there in these areas where we can get to the actual rim joist, even though it's along the same wall, and the same inches of depth away from the outside of the house. (shrug)

The fiberglass batt's that are between the concrete walls and the drywall extend from down below up to near the top of the rim joist. But it's just the top of the batt's. They appear to be providing even worse insulation than the standard small-cut pieces jammed into a rim joist area.

I'd like to put our XPS blocks in this area too, but these batts are blocking access.

My immediate idea was to just push/scrunch the batts down far enough so the blocks would fit, but then I realized that would probably cause it to bunch up, not being as flat against the concrete wall, and decreasing its effectiveness.

My other thought is to cut the top off of these batts. But, I know that wouldn't be a fun job.

What would you do?
 
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  #2  
Old 08-21-11, 08:21 PM
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Any time you compress insulation, you reduce its R-value. Does that answer your question?

Also, the plural of batt is batts. Apostrophes are for possessives and contractions. Yes, that's a pet peeve.
 
  #3  
Old 08-21-11, 08:50 PM
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Yeah, that does help actually. Do it right, cut the offending area off the batts, and deal with the mess. Good point about "batt's".
 
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