Insulating a 2x2 wall - AVS Forum
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post #1 of 9 Old 05-06-2003, 06:27 AM - Thread Starter
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Due to space limitations, I'm framing the foundation wall (cinder block) of my basement with 2x2's. (The other 3 walls are interior walls and will be 2x6 staggered stud construction.) I'm trying to figure out the best way to insulate this shallow wall. The way I see it, I have 3 options:

1. Use regular 3 1/2" batts, and just compress them in the joint cavity. Under normal circumstances, this is an installation no-no, since it will reduce the R-value of the batts I use.

2. Use regular 3 1/2" batts, but peel away roughly half of their thickness to accomodate the shallow wall space. Again, this will obviously reduce the R-value.

3. Go with blown-in cellulose. Somewhat more of a PITA (have to rent the machine etc.), but I'll have just the right thickness for the wall.

I'm wondering if any of the three alternatives are better/worse than the others, or if I'm just going to wind up with the same R-value at the end of the day.

Kirk

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post #2 of 9 Old 05-06-2003, 07:35 PM
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Interesting question. So I went to the book.

When you compress fiberglass you decrease the overall R value of the Batt.
However you INCREASE the R value per inch. So if you start out with a R11 Batt intended for a 3 1/2 inch space and compress it to 2 inches you end up with about R 7 according to a graph in the "Visual Handbook of Building and Remodeling"

Now if you peeled the the R 11 in half you have about R 5.5. So if my math is correct stuff away.

Some other things to consider.

a cinder block wall with 2x4 construction and fiberglass yields a total of R 12.3

a cinder block wall with 2 inches of foam is R 14.4 (no studs)

The wood studs have a poor R value, I think there is a construction technique where the foam is glued and fastened to the walls and the drywall to the foam. You might want to investigate if R value is important.

Another thing to consider is whether the wall in question is above or below grade. The deeper the better since it will mitigate both the severe cold and hot extremes.

I couldn't find any info on a blown insulation wall for masonry walls ...maybe it's not a good idea. It has an R value of 2.8 to 3.7 per inch versus 3 to 3.8 for fiberglass.

Phenolic rigid board is 6.5 to 8.3 per inch (the highest in the table) but I don't have a clue as to what it is.


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post #3 of 9 Old 05-06-2003, 09:14 PM
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I used owens pink foam foundation insulation. Basically looks like pink styrofoam 2" thick sheets, comes in 4x8 sheets. You just cut it to fit between the 2x2's. In Kansas our frost line is down to about 32" roughly, so thats as far as I went down from the top of the wall with the foam. The theory being that anything below that had no effect. Looking back it would not have been a bad idea to go alll the way from top to bottom because the foam acts as a great vapor barrier. Oh, by the way all you have to do is liquig nail it to the wall. Pretty easy stuff to work with and it doesn' t get you itchy. The one question I never got answered is how it effects the sound of your room. My theater is still being sheetrocked, so I cant tell yet.

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post #4 of 9 Old 05-06-2003, 09:16 PM
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Oh, by the way, my foam was R 7.5. I think it also comes in R 10.

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post #5 of 9 Old 05-07-2003, 05:28 AM
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Here is a place for useful info on insulating

http://doityourself.com/insulate/


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post #6 of 9 Old 05-07-2003, 07:03 AM - Thread Starter
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Thanks for the replies. I think what I'll probably do is compress batts of R-13 in the wall cavity. That way I'll likely achieve R-8 or 9.

I'm also considering the products from Roxul, which are supposed to have excellent acoustical properties. I'm more concerned with having a resonant cavity in the wall than with true insulation properties. The wall is 75-80% below grade anyway, and I'll have enough heat in the theater during the winter.

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post #7 of 9 Old 05-07-2003, 09:23 AM
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How do you run cable/romex in a 2x2 wall?

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post #8 of 9 Old 05-07-2003, 01:04 PM - Thread Starter
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I will likely run it behind the wall (between the framing and the foundation). Alternatively, if I have to, I'll run it along the top plate (which does not come into direct contact with the ceiling/floor joists for de-coupling purposes) and then through the top plate at the desired locations.

I'll post some pictures when I get to that point. After several weeks of demolition, and a brand new HVAC system, including all new duct work (to keep it all outside of the theater), I've now begun construction. The aforementioned 2 x 2 wall has been framed, but not yet raised in place.

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post #9 of 9 Old 05-07-2003, 04:15 PM
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You can use the pink foam or foam boards that come in 1 inch thickness and stack them for the 2 inches. Try and get the 4 by 8 boards that have a reflective surface like aluminum foil. You might consider one inch of the foam board for thermal insulation and the second inch of sound proof board for the second inch.

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