The remedy for thin walls - cellulose accoustical insulation

Q. Is there a way to treat a Sheetrock wall between our apartment and the one next door that would reduce noise? - W.W.W., Charlottesville, Va.

A. Howard Clark, a construction supervisor in Hopkinton, Mass., recommends investigating the makeup of the wall, and then discussing price options with your landlord.

Check if there is insulation against sound in the wall already. Do this by removing switch plates and outlet covers on walls separating you from your neighbors. Examine the drywall where it is cut around these electrical boxes.

If the wall cavity is empty, you can blow a cellulose acoustical insulation between each cavity formed by the wall framing through holes made in the drywall at the top. A machine (something like an oversized vacuum that works in reverse) can usually be rented from a lumber yard that supplies the bagged insulation. The holes can be patched or covered with trim.

If the wall has insulation, albeit too little, add sound-dampening layers - fiber-board sheets are typical - over the wall surface. These can be cut to size, covered with fabric, and tacked to the wall, running floor to ceiling. For best results, both sides of the wall should be covered like this, or doubling a layer is almost as effective. Installing the fiber board on nailing strips so that there is an air space between the wall and new panel will improve performance.

But before adding layers on the outside of the wall, it's important to check with your local building inspector or fire marshall. They may wish to review the panel's flame-spread rating. (Your supplier will have this information.)

In the worst case scenario, codes in your area might require another layer of drywall over the sound board if it's too flammable for exposed use in a multifamily structure.

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