Sat, Jan. 19, 2002

Can attic insulation hinge on snow?

ALLEN NORWOOD

A dozen readers called to ask whether snow melting quickly on their roofs meant they needed more attic insulation. The answer is, well, perhaps.

Lots of variables might have caused our recent snow to melt faster on one roof in a neighborhood than on another. The angle of the roof to the sun, for instance, or shade from evergreen trees. Attic ventilation plays a part; so does the location and airtightness of ductwork.

But most of a home's heat escapes through the ceiling, said Keith Thomas of McKee Insulating. So if all other things are equal, and the snow on your roof melted far faster than on your neighbor's, then you're losing more heat.

"The heat is going through the insulation and heating the roof of the attic," he said.

Recommended attic insulation in Charlotte is R-30, Thomas said. Generally, that means about 13 inches of blown insulation or 10 inches of batting. The R-value is the ability of insulation to retard the flow of heat.

Charlotte attics need lots of proper ventilation, too, even in the winter.

Ventilation is especially important in the summer, Thomas said. Too much heat in the attic can cause shingles to curl and fail prematurely. Roof areas over raised ceilings are particularly vulnerable.

"A lot of the time, if you look at a roof and shingles are starting to curl in one area, and another area right beside it is fine, most likely they've got a cathedral ceiling right there."

In the winter, ventilation helps prevent moisture from building up in the attic. Moisture can cause all sorts of problems -- such as reducing the insulation's R-value.

The best ventilation is a soffit vent that runs the full length of your house, Thomas said, combined with a ridge vent.

So, if you noticed that the snow melted quickly on your roof, here are a few things to check:

• Measure your attic insulation in a couple of spots to make sure you have enough.

• If you have ductwork in your attic, be sure it's sealed and insulated.

• Insulate the backs of access hole covers and attic fans.

• Be sure soffit vents and ridge vents are clear so air can flow freely. Be sure insulation isn't piled so deeply at the edges of your attic that it blocks airflow.