Third layer of asphalt shingles a no-no

Q. I have a question about roofs. Our home is due for a new roofsoon and we are getting different bids for the project.

The least expensive of the bids involves installing new shinglesover the existing shingles. One roofer said I already have two layersof older shingles and a third layer would place too much weight onthe roof.

He wants to remove the first layer of shingles before adding newones. His price is significantly higher than the others. I'mconcerned with his remarks that the extra weight could cause the roofto fall.

Is he just trying to frighten me into a more costly repair?

A. I will try to help you, but you did not give me enoughinformation to make a definite determination.

With that said, most roofs should not have more than two layers ofasphalt shingles. I have seen steep-pitched roofs with three layers,but the home's roof system had extra bracing in the attic to supportthe added weight of all the shingles.

In most cases, the costs of adding extra bracing might be morethan the costs for the removal of the two layers of shingles, but theroof system would always be braced against strong winds and deep snowcover.

On average, a common asphalt shingle weighs 240 pounds per 100square feet. A small, single-story home measuring 24 feet by 40 feethas 960 square feet of floor space.

If the roof were a simple gable style with a moderate pitch, theshingles would weigh in at 2,880 pounds. Adding a second layerdoubles that weight. A third layer could cripple the roof.

Also consider this: As you add layers of shingles, the lifeexpectancy of that layer decreases and the manufacturer's warrantywill be void. If the home has only one layer, you might consider oneof the new steel roof panels that weighs much less than an asphaltshingle, has a 40- to 50-year warranty and is 19 percent cooler thana common asphalt shingle.

According to the Florida Solar Energy Center, a steel shingle willreflect anywhere from 66 to 77 percent of the sun's energy, makingthe attic space much cooler. Steel panels also have a class 4 rating,which is the highest rating available against hale damage. When thepanels are screwed in rather than nailed, they can resist winds up to120 miles per hour.

Make sure the roofer is experienced in installing steel panels andthat a felt paper is applied to the old asphalt shingles beforeinstalling the steel panels. The felt paper protects the zinc coatingon the underside of the steel panels from being scratched by thesandy granules on the old shingles. If the zinc is scratched, thepanel could start to rust from the backside.

Steel roof panels come in a variety of sizes, shapes and colors.Most makers claim the colors do not change or fade with time, butonly time will tell.

Dwight Barnett is a certified master inspector with the AmericanSociety of Home Inspectors. Send home improvement questions to:Dwight Barnett, Evansville Courier & Press, P.O. Box 286, Evansville,Ind. 47702.