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Letter to the editor

Amount of home insulation trumps type

By James Dulley, Special to the Times
Published October 20, 2007

A: Proper insulation is imperative for reasonable utility bills. It not only reduces the energy loss in winter or gain in summer, but it can also make you more comfortable by keeping the indoor wall surface warmer during winter or cooler during summer. It's very uncomfortable to sit near a cold, uninsulated exterior wall during winter.

The amount of insulation is generally more important than the type you select. This is particularly true in the attic, where the amount installed is not limited by the width of the opening, as it is inside of a wall. Your local insulation contractor, utility company or building inspector can tell you the recommended amounts for your climate.

Although you often hear the amount of insulation quoted in inches, the true measure of insulation is its installed R-value. The insulation value of different insulation materials varies significantly. Some foam insulation materials can provide almost twice as much insulation R-value per inch thickness as do standard batts.

When you talk with insulation contractors, make sure they quote the R-value of the insulation you are getting. Particularly with blown-in, loose-fill insulation, the density can be too low. This means you get a lot of inches of depth, but the resultant insulation R-value is not as high as you expected.

For your attic, blown-in insulation is always a good choice. This can be fiberglass, rock wool or cellulose. When installed properly, the R-values per inch thickness are similar for these three materials. Check for baffles by attic soffit vent inlets so the insulation does not blow over and block them.

For the walls in your new room, consider batt insulation if you are doing the insulating yourself. Batts with the vapor barrier already attached are simple to install. I use batt insulation made from recycled cotton denim waste. The cotton is treated for fire safety.

Sprayed-on urethane foam insulation offers the highest insulation levels for limited space inside a framed wall. Closed-cell foams are best. Another option is blown-in fiberglass or rock wool mixed with a resin. Once blown into the walls, the resin sets up and so it will not settle. If the wall is already closed in, standard blown-in insulation is a good option.

For both the new and existing walls, adding rigid foam board insulation to the exterior is best because the entire wall structure is within the insulation envelope. Any type of exterior finish can be applied over it.

James Dulley is a mechanical engineer and do-it-yourselfer. Send questions to James Dulley, The Sensible Home, St. Petersburg Times, 6906 Royalgreen Drive, Cincinnati, OH 45244. Visit his Web site at www.dulley.com to tour his energy-efficient home, post questions for other readers and find other information.

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Insulation suppliers

These companies offer insulation materials:

- Bonded Logic, (480) 812-9114, www.bondedlogic.com.

- Certainteed, toll-free 1-800-782-8777, www.certainteed.com.

- Corbond, toll-free 1-888-949-9089, www.corbond.com.

- Johns Manville, toll-free 1-800-654-3103, www.jm.com.

- Thermafiber, toll-free 1-888-834-2371, www.thermafiber.com.

[Last modified October 19, 2007, 09:28:35]