When replacing a roof, most people opt for three-tab or laminated fiberglass shingles (both are a type of asphalt shingle named after the substance that holds them together). In less than 10 years, extreme temperatures and sunlight can crack, curl, and split shingles, rain and sleet can wear them down, and wind can tear them apart. But they can last much longer--25 years or more--if you choose the right kind, and the right installation.

WHAT'S AVAILABLE

Major brands of fiberglass shingles include CertainTeed, GAF, Tamko, and Owens Corning.

Fiberglass shingles (sometimes still called asphalt shingles) are essentially large rectangles made of fiberglass mats coated with asphalt. They are coated on the bottom surface with sand, talc, or other mineral fillers to make them stiff and to counter the asphalt's stickiness. The top surfaces are typically coated with granules colored with a hard ceramic glaze. These granules also protect the asphalt from the sun's ultraviolet rays and add weight to the shingle so it can better resist wind.

Since asphalt shingles first appeared more than 80 years ago, they've mostly been the same familiar three-tab format--a piece of shingle made of three 12-inch-wide tabs separated by slots. Asphalt shingles with a fiberglass mat instead of the traditional organic mat came out in the early 1970s.

Laminated shingles (also called "architectural" or "dimensional") are a more expensive type of asphalt shingle. They commonly consist of two or more shingle layers laminated together to create a three-dimensional effect that mimics wood or slate in each laminated shingle. They tend to weigh more than three-tab fiberglass shingles.

The usual shingle size is 12x36 inches, though "metric" shingles (13x39 inches) are also available.

Some manufacturers also make shingles that have zinc or copper particles mixed in with the surface granules. These metal oxides help prevent the formation of algae, which can be a problem in some regions. Homeowners who have seen black streaking on their roof should consider algae-resistant shingles for their next replacement.

Shingles are sold in "bundles" that typically contain one-third "square" of three-tab shingles (a square is enough to cover 100 square feet) and one-fourth square of laminated shingles.

Price range: $30 to $60 per square (190 to 240 pounds per square) for three-tab; $40 to $140 per square (260 to 450 pounds per square) for laminated.

HOW TO CHOOSE

Performance differences. While laminated shingles did better than three-tab shingles overall in Consumer Reports tests, the best three-tab shingles rival the best laminates in performance and cost as little as $30 per square. They can be a satisfactory choice if you're looking to curb costs.

Three-tab shingles generally have a 20- to 30-year prorated warranty. Some manufacturers also provide full-replacement value for 10 years. Prorated warranties for laminated shingles often run even longer--sometimes for the life of the house.

Recommendations. Fiberglass shingles are a long-term investment, both from a quality and aesthetic standpoint. When deciding to put on a new roof, consider how long you'll stay in your house. If it's only a few years--and the existing roof isn't that bad--you may want to let the next owner take on this expense. And even if you'll be staying there for a while, consider how the shingles you choose will affect your home's resale value down the road. That may mean balancing your personal taste with the need for your home to fit in with others in the neighborhood.

New shingles can be placed over a single existing layer that doesn't show signs of damage. (Look for damage from within the attic, or check topside for soft spots or undulations.) Don't add a third layer; the rafters may not support the weight and it may be illegal in some locales. Shingles should be nailed (four nails per shingle in most areas, six where it's windy), not stapled.

Even the best fiberglass shingles won't last if the plywood or solid-board sheathing beneath them is in poor shape. When installing new shingles, replace any rotted, warped, or split sheathing. Also replace or reinforce any rafters that are badly cracked or bowed. Proper attic ventilation is also a key to long-lived roof shingles, since excess heat buildup can hasten their deterioration. Have the installer eliminate any air-flow obstructions around the soffit, ridge, and gable-end vents.

Replace all roof underlayment and flashing when a complete tear-off of old roofing is done. Buy an extra bundle of shingles so you'll have matching shingles handy for spot repairs.

Before you sign the dotted line, see that the contract spells out all details. Ask the roofing contractor for the shingle manufacturer's warranty--especially the full-reimbursement period, which is more meaningful than the total warranty. And keep a wrapper from one of the bundles of shingles so you can identify exactly what was installed should you need to use the warranty.

Many brands are now "certifying" installers who can offer a labor warranty at an additional cost. Be sure to obtain proof of this certification from the installer.