Exterior wall insulation

Q. Our century-old, 1 1/2-story farmhouse has been adequately insulated everywher except over a 4-foot knee wall. Now I want to apply new asphalt shingles over the wall but want to insulate it first. What shoud I use? Peter V. Rogers Novelty, Ohio

A. Rigid exterior wall insulaton is the ticket. There are a numbe of manufacturers of thermal-type wall sheathing, including Johns-Manville, OwensCorning, and Celotex.

Sally forth to a building supply dealer and make your choice. Inspect and select a rigid exterior insulation board in a thickness and with an R factor as high as is practical under the circumstances. The thickness of the insulation will determine the length of nails which you will need in applying the new shingles.

Likely the existing shingles could remain in place underneath the new rigid insulation board.