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russd772 08-13-2013 08:13 AM

Using attic insulation in interior walls.
Hello all,

I recently started a project to replace the old plaster walls in an upstairs bedroom. It started as a paint job but upon removing the wallpaper I noticed some severe water damage to the walls and a lot of large cracks. so I am on a really tight budget as I was not expecting this project to be so involved. I gave this information just as background information because I have two options right now. use the insulation I have or rip it out and use nothing.

I bought the wrong stuff from the store, I got R-30 attic insulation instead of a lower R value for interior walls. I know that the compression will hinder the ability of the insulation to work to its full potential, I got this stuff because it was 12 bucks a roll opposed to 60 for the next stuff up, and insulation is insulation.. right, apparently not.

I also screwed up on the moisture barrier and put it between the outside wall and the insulation, instead of between the insulation and sheet rock.

My main question here is will this setup cause any hazards, like fire, mold, ect ect. or am I ok, just not going to be the best at insulating the room.

sorry for the long post on such a short topic, in my experience I usually get a better answer from people when they have more information.


strategery 08-13-2013 08:22 AM

You put the vapor barrier toward the outside? Are you in a cooling dominated climate?

russd772 08-13-2013 08:25 AM


Originally Posted by strategery (Post 1228701)
You put the vapor barrier toward the outside? Are you in a cooling dominated climate?

do you mean using the AC most of the year? if so then no. I live in main we run the furnace for heat 7 months out of the year. I just messed it up. someone told me that it was needed and I figured that it was to keep moisture from coming in the house from outside, so I put up against the outside wall. I realize now its more about condensation

strategery 08-13-2013 08:28 AM

Yeah you want it to the warm side. It's important do moisture doesn't condense inside the wall cavity

russd772 08-13-2013 08:32 AM

what about the type of insulation im using do you know about that? someone said the attic insulation retains moisture, will this not be an issue with the proper moisture barrier in place?

also do I need to remove the plastic I have up now or will that be ok to stay?

joecaption 08-13-2013 08:50 AM

Compressed insulation will be useless.
Take it back and get the right stuff.
If it's 2 X 4 walls you need R-13, 2 X 6 will be R-19.
If this is an old balloon constructed house you should have installed fire blocking at the top and bottom of the walls.
All holes needed to be sealed with expanding foam before insulating.
Good time to up date or add outlets while that wall is opened up.

Gary in WA 08-16-2013 12:15 AM

1. Was it a asphalt facing? Or a poly or foil? Describe the wall make-up.

2. Compressing insulation increases the density, a good thing --- to stop air movement/convective looping (inherent with R-19, the biggest loser), pp. 45-47; http://www.buildingscienceconsulting...Measure_Up.pdf

R-30 @ 9-1/2" is compressed (by the manufacturer) to R-25 @ 8" and again compressed to R-21 @ 5-1/2" again comp. to R- 15 @ 3-1/2" each time the density increases as the thickness decreases = less R-value for the wall---- but the R-value per i9nch increases--- R-30 starts at 0.5#/c.ft. to R-25 @ 0.7#/c.ft. to
R-15 at 1.4 #/c.ft. :

R-19 (low density) is compressed to R-13 (medium density); pp. 68;

This explains better- starting with a low density R-30, compressing it to ------ lol. too tired, too late, read the densities;

R-30 is R-21 in a 2x6 wall and will stop a lot of air with no convection due to higher density;


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