How to insulate a cellar wall
Q. My poured concrete basement has an 8-inch-thick wall with a 10-inch exposure above ground. Heat loss already is minimized by weatherstripping and plastic sheets. There is, however, considerable heat loss through the cellar walls, especially the upper half. The conventional solution is to install 2-by- 3 or 2-by-4 studding filled with batt insulation. I have also considered and rejected the use of polystyrene panels because of the problems of flammability and toxic fumes. If I were to cover the styrene with plasterboard, I would be right back with the problem and cost of a framework that is adequate to support the weight. I wonder if it is reasonable to install 4-by-8 sheets of Celotex wallboard to cover the upper four feet of the wall. What adhesive should I use if the whole idea is practical? R. I. Mitchell Plymouth, New Hampshire
A. Celotex denotes a wide range of ceiling and wallboard products of varying thickness and insulating values.
You are correct in saying that attaching this sort of material to the upper half of the basement walls would produce some insulating effect. However, the trick lies in locating the most value for one's purchasing dollar.
Investigate the many similar materials on the market with an eye toward the one with the highest insulating, or R, value.
Use a waterproof mastic cement to apply the board to the inside walls. A double thickness of the wallboard would obviously increase the insulating value.
One insulation contractor says he would use a rigid fiberglass board, two inches thick, and glued to the interior wall surface with a product called Tuff-bond, or equal. Both products are available through a local mechanical insulation supplier.
The R value is greater in the rigid fiberglass than with the Celotex.
My calculations show that you would need less than 400 board measure of 2-by- 4s which, out here in California, would cost less than $200 at retail.
If it were my basement I would apply the studs to the walls with glue, install the best R- factor insulation commensurate with 4-inch nominal thickness , and cover the studs with whatever finish material suited by fancy and budget.
If possible, install an asphalt-impregnated insulating fiberboard below grade outside and against the perimeter foundation to the frost line. That will thwart much of the cold which otherwise is passing through the upper portion of the wall.