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Dense packed cellulose inside foam for basement insulation?

I plan to insulate my now uninsulated poured concrete basement walls. I think I have a pretty good idea of how it should be done using XPS on walls and floors, wood framing inside the foam and with further insulation between the studs,, with a code compliant fire "retardant' cover like drywall. I base my plans on research here, at Fine Home building, and at Building Science Corp.

My question is whether it would be okay to use dense packed cellulose between the studs? I can't seem to find a good answer to this question anywhere. Obviously, there are potential issues with water in a basement but from what I've read, the ability of cellulose to absorb and then release water to/from the air is seen as an advantage of its use. I know I could use fiberglass or a mineral-based insulation but I'd prefer to use cellulose as long as it won't cause problems.

Thanks.

Asked by Andrew Alden
Posted Thu, 10/13/2011 - 15:40

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4 Answers

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1.
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Andrew,
Don't do it. If you are insulating your basement, there is absolutely no benefit to choosing an insulation that has the ability to absorb water.

Basements often suffer flooding events or incidents of water entry. I always advise anyone insulating a basement to use only rigid foam or closed-cell spray foam.

If you want more R-value, just add thicker foam to the walls. Then you can build your stud wall to hold your electrical wiring and to support your drywall or cement backerboard. Just be sure to leave the stud bays empty -- without any insulation in them.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 10/13/2011 - 16:00

2.
Helpful? 0

Martin. Thanks on the cellulose answer.
I'm having trouble understanding why I shouldn't take advantage of the stud bays for insulation. Adding additional foam thickness to the walls diminishes interior space. Even if I wasn't to use a fiber product couldn't I use additional foam in the stud bays?

Answered by Andrew Alden
Posted Fri, 10/14/2011 - 09:12

3.
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Andrew,
Sure, you can use the stud bays if you really want to. The easiest insulation to install would be closed-cell spray polyurethane foam. A more fussy approach would be to install narrow strips of rigid foam with the perimeter of each piece sealed with caulk or canned spray foam.

Either approach will, of course, complicate future changes to your electrical wiring.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 10/14/2011 - 09:18

4.
Helpful? 0

I'm now well acquainted with the "fussy" approach you mention above. I've been insulating some cantilevers on my house using this method. Working with canned foam overhead is no fun!

Thanks for you timely response.

Answered by Andrew Alden
Posted Fri, 10/14/2011 - 09:23

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