Insulation offers some protection from noise

Dear Jim: Our house walls need more insulation and they should be more soundproof. We are also planning to add on a bedroom. Will insulation make the existing rooms quieter and the new room more soundproof? – Bob J.

Dear Bob: Adding wall insulation to save energy helps somewhat to soundproof the walls from outdoor noise, but you need additional changes for a significant improvement. If your windows are old, installing new ones makes the greatest improvement in blocking outdoor noise and saving energy.

Soundproofing a room is a subset of making it quieter. Soundproofing refers to blocking noise from outdoors or adjacent rooms. To have a quiet room, also consider the acoustic properties inside the room. Quite a lot of sound is generated inside a room by plumbing, air from registers, clocks, voices and movement.

The soundproof quality of a wall is rated by STC (sound transmission class). A higher STC number indicates a more soundproof wall. A typical interior wall with drywall on each side of two-by-four framing has an STC of about 34. If there are common heating ducts, holes for electrical outlets and phone jacks, the STC of that interior wall may be only 25. Adding insulation inside the wall increases the STC by very little. Normal conversation can easily be heard and understood through this wall. At the other extreme, with an STC of 66, yelling can barely be heard in adjacent rooms.

Your first step in soundproofing interior and exterior walls is to get out the caulking gun and seal any open joint and gaps in the walls. This isolates and blocks the free movement of vibrating air (sound). On exterior walls, this also reduces outdoor air leakage to save energy.

Decoupling the two surfaces of a wall is critical to block sound. This means not allowing the two wall surfaces to be rigidly connected through the wall studs. One simple method is to install a second layer of drywall on the existing one. Make sure not to screw it into the wall studs so it stays decoupled. This method also increases the mass of the wall.

Another method to decouple walls is installing thin resilient metal strips over the studs. The new drywall is attached to these strips and not directly to the studs.

Consider installing a strong soundproofing board made of recycled materials, such as Homasote 440, over the studs. Screw the drywall or resilient channels to this board.

Dear Jim: I have a direct-vent gas fireplace installed on an outside wall. When it is not being used, there is a strong cold draft coming from beneath the control panel. How can I stop this chilly draft? – Mike M.

Dear Mike: A direct-vent fireplace should have sealed combustion with a single inlet-outlet pipe going through the wall. If it is caulked where the pipe goes out, no outdoor air can get into the room. You probably have air leaking in somewhere else and it is blowing out under the fireplace. Turn the electricity off and remove an electrical faceplate on that wall. If you also feel cold air coming in, search for and seal any exterior leaks in the wall.

Send inquiries to James Dulley, Bangor Daily News, 6906 Royalgreen Drive, Cincinnati, Ohio 45244 or visit www.dulley.com.