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

darlingm 08-21-2011 04:43 PM

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.

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.


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?

Gary in WA 08-28-2011 02:31 PM

Picture would help immensely...


Windows on Wash 08-30-2011 12:26 PM

By the time you spend the time doing all that, you might be better served to just by a small two part spray foam kit and apply it that way.

It will be much faster and will provide the proper air seal that you may not be able to get with the rigid and straw foam.

It will be a bit more expensive but it will go much faster and do a much better overall job.

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