"Room within a room" vapor barrier ??s

Hi,

I am building a "Room within a Room" (RWAR) for a Home Theater in my basement. I have a couple questions regarding the vapor barrier required for this setup.

I have a walkout basement so some walls of the RWAR will be framed in front of these exterior framed walls. The exterior walls are insulated with R-19 and have a foil barrier installed. I was going to replace the foil barrier with a 6mil poly barrier. Is there a difference between the two? COuld I put up the POly first then lay the foil over that? Or would that be bad?


Also Would I also put a vapor barrier on the inside of the RWAR? Some walls of the RWAR are in front of the cement walls so wouldnt those need a barrier too?
I guess my concern is that would it be bad to have one vapor barrier on the external wall.... then an air space... then a wall framed with a vapor barrier to the interior of that wall.

Thanks for any help.

Lou

 

Lou,

THere is no need to double vapor barrier. It is best to ensure that only vapor barrier is placed on the farthest exterior wall for the purpose it is designed for.

More than that would/could create a problem leaving an void to prevent air flow and thus if any moisture ever became present, mildew issues might arise.

You could call your Local Building official to confirm this advice.

Hope this helps!

 

Thanks that helps alot.

Just curious.. for the walls that are framed in front of a half concrete/half framed exterior wall... should I put a vapor barrier on the newly framed wall?

Whats the preferred Vapor Barrier... foil or poly?

 

Apply the poly the same as you would on regular walls. THis would be on the studs behind the sheetrock.

I would use poly versus foil but this depends on where you live.

Hope this helps!

 

thanks for your help.

Last week when we had below 0 temps here in CT my walkout basement - framed walls had some frost on the outside of the vapor barrier (interior of room). Is this a problem or is this normal?

Eventually the basement will be heated.

 

buggdog,

I wrote this awhile back,

"I guess this is the best and most economical way to construct walls that would be placed on the exterior. I prefer to see 2x4 but as mentioned by others they can get 2x3's. You still need that W/T BOTTOM PLATE. The best way is to attach WOOD TREATED BOTTOM PLATE to the concrete is to use either...
Concrete nails - Sometimes this is hard and time consuming!
Tapcon Screws - Relatively easy but again time consuming!
Hilti Gun with ramset nails - Rent the gun, buy nails and charges - Very fast and holds great! - No adhesive is needed.
Doing the wall framing 16" O.C. provides a solid base for your 1/2" drywall. If using traditional framing method, frame your new wall 1" from the vertical block/masonry surface if using R-13. The reason to keep the wood out from the walls is the moisture that could damage them. If using insulation like R-19 and only 2x4 studs, the insulation would touch the walls. I have stated before that if a homeowner did put thicker insulation in, and the wall was only 1" from the masonry surface, I have recommended hanging a vapor barrier between the back of the wall and masonry surface. This doesn't allow for the insulation to touch the wall and air movement is not restricted but at least you won't create damage to the insulation or wood.
Vapor barrier should be placed directly under the drywall. The warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity. If enough of this happens, and the water cannot escape, wood rot, mold, and other moisture-related problems are likely to occur. For this reason, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity. This is what is required in Minnesota;

"A 4 mill poly vapor barrier must be placed against all concrete or block exterior foundation walls prior to applying furring strips for full height of the wall. Another 4 mill poly vapor barrier must be placed over furring strips and insulation prior to covering with finish materials. (State Energy Code Requirement)" - MINNESOTA CODE

***PLEASE NOTE THAT YOU MUST MAKE SMALL SLICES AT GRADE LEVEL ONLY FOR WEEPING IN THE POLY IF POLY IS PLACED AGAINST THE BLOCK - ATTACH THE POLY WITH STAPLES TO YOUR JOISTS/FOUNDATION SILL PLATE***

If you do want to increase the R value, move the wall out further or use the R-13 and then apply a rigid insulation over the studs (warm side) then drywall (not paneling) *Code advises a 15 minute fire rated material over any rigid insulation - 1/2" Drywall*..

Kraft Faced insulation is fine to use in the above scenario. No need for the poly and you can do everything easily. You may find this easier and I would do this versus unfaced and vapor barrier because I don't like to play with it any more than I have to."


Hope this helps!