Insulating interior surface of old walls
In my 1890 Queen Anne Victorian, a previous owner installed dropped ceilings and blew in cellulose wall insulation up to the 8ft level, leaving the upper 2 feet uninsulated. I have torn out the drop ceilings and what was left of the old ceiling plaster. In the kitchen the wall plaster was so bad, I pulled it off the lath. The insulation behind that lath has so many voids I estimate it only covered 60 to 70 % of the wall. I plan to redo the insulation in that wall. My question is, in the other rooms, the plaster is in much better shape, needing only moderate repairs where the drop ceilings were attached. With the cost of heating, (as much as $450 per month) I’m considering adding an inch or two of Thermax in addition to filling the bays to the 10 ft level with blown in cellulose. With one or two inches of foam on the interior of the studs, and a layer of sheetrock installed with long screws, I could achieve R-18 with one inch, R-26 with two inch. This would require extending window jambs, and reworking baseboard and picture molding. My concern (other than wasting my hard earned money and labor on unnecessary additional insulation) is: what kind of problems can this create? I haven’t seen any descriptions of using the material this way?
Replies
Over the past few years, in renovations such as yours, a lot of the contractors in my orbit have been using closed-cell, sprayed on foam. No vapor barrier needed.
I have even seen it sprayed in attics without vents, then sheetrocked with no air channels.
i will be interested in what some of the pros around here think of this approach. The building inspectors here are fine with it.
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"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
I may end up going that route. Was hoping to do it myself. Its a big house, and I have to work full time to earn enough to do the work.
There's only one contractor in the area who does the spray installation.
Thanks for your thoughts.
If you do the Thermax thing, use 5/8" rock. It is lots stiffer than the 1/2", so screw pops are less likely due to local deformation of the Thermax whan the wall is struck.
Really tight houses done like this sometimes have small mold spots over the screw heads because moisture condenses there first. The screws are a conductive path through the insulation. Some, but not all...many variables.
Bill
Thanks.