Insulation, Radiant and Vapor Barriers - Cold Wall Problem Solvable with Interior Styrofoam?

I have a 1965 house with poor wall insulation. One windowless north-facing wall is particualry bad and I would like to fix it. The wall is exterior brick on a wood frame with interior drywall. I am thinking of adding 1.5 inch styrofoam sheeting on the interior of this wall and applying a second layer of drywall over it. Is this OK to do? Will there be any vapor barrier issues (since the wall will now have two vapor barriers, one on the old fiberglass in the wall and the new styrofoam as well).

I am thinking of doing the same thing. - 2" extruded polystyrene on the interior. I am also planning to do my vaulted ceilings since there is no room for any more insulation between the scissor trusses. This approach will give me true, positive insulation that is not afforded by the leaky stud/fiberglass system that never practically recognizes the infiltration, different heat loss through studs and the pink stuff and the shift of the dew points.

I was planning on removing the old sheet rock and polystyrene, but your approach is less mess. I recognize there should be a vapor barrier in the form of poly, but I sincerely doubt the real efffectivemess of the existing barrier from a practical standpoint. I am sure it was compromised many times at edges, tears, outlets even if there is no window or door.

My latest thinking is to leave the old sheet rock in place and poke or drill holes through the poly to insure it is compromised and cannot perform as a vapor barrier.

In all the code and standards committees I have been active on, I realized that the concepts heat flow and moisture flow are all too idealistic and are totally erronious for some locations with climate swings. On top of this, they are for steady state conditions that do not exist. The insulation peddlers are as bad as the ivory tower professors. We seem to be a victim of advertising.

I hope I can tag on your thread to borrow some opinions. I have observed there are many opinions (as many as there are for unique sutuations).

Dick

Is your reason for not removing the original layer of drywall simply to avoid the mess and hassle?

You're talking about putting up a new layer of drywall anyway, so all you're saving is the demo work, yes?

It seems to me that you lose the option of insulated the wall itself.

Rip down the original wallboard, modify the existing insulation if you feel the need, and if you so choose, put up the foam. You very well might get away with just adding new fibreglass bats and save the 3 inches of space in the room, no?

I think instarx thread was questioning applying rigid foam over the existing wall consisting of fiberglass bats and a vapor barrier, resulting in an increased level of insulation, but having two vapor barriers. There currently is insulation, but it is not adequate.

My situation is the same except that I am doing the ceiling also. In both cases, the goal is to upgrade the wall by adding isulation to the interior of the wall. Exterior insulation is out for me because of townhouse architectural requirements and adjacent units. The scissor trusses (vaulted ceiling) do not permit adding a reasonable amount of insulation without ventilation problems.

Removing the interior sheet rock and vapor barrier is possible for me since I will be trashing the ugly new carpet put in by the previous owner less than a year ago to make it a more attractive listing. Losing 2-1/2 inches of space is no big thing.

One key question is can you destroy an existing vapor barrier without ripping off the interior?

With the projected cost of fuel, I imagine many other people will attempt to increase the insulation level of walls (mainly 2x4) that are already insulated

Dick.

Yes, my reason for not removing the existing sheetrock is for simplicity of installation and to avoid the demolition work. I would agree it would be best to remove the sheetrock and install good insulation correctly between the studs, but oh that demolition work! Plus I really hate working with fiberglass.

I like the idea of disabling the existing vapor barrier before adding the interior styrofoam by just tearing the paper through holes drilled in the existing drywall - thanks for the idea. That should eliminate any problem with having two vapor barriers in the wall.

I think I understand. I know in our current house the wall insulation was originally (1969) something like R5 (1.5" batted insulation).

At least in our situation, It didn't seem to make sense to avoid the demo work when the possible gain is ~R16. (R5 => R21) If you still want more, then you can apply the foam directly to the studs.

If you're removing the wallboard from the entire wall it really is easy if the wall is old (nailed vs. screwed). Only issue is disposing of that much wallboard. That tends to be a pita.

if you are going to kill the drywall any way why not go the extra mile and spray foan the place after taking out the batt insulation? rigid foam is not cost effectively cheaper over sparay any more when you consider the labour and other extras. I would venture to say that you risk trapping moisture in that layer of sheet rock as it will likely act as a wick for moisture. also keep in mind you will loose about 6" of living space from your house do you really want to do that??