The majority of residential roofs in the United States are covered by asphalt shingle roofing. They come in two types - organic base and fiberglass. Organic base means that the shingles are made of a cellulose mat saturated with asphalt and covered with mineral granules. Fiberglass shingles have a mat of woven glass fiber saturated with asphalt and covered with mineral granules.

Organic-base shingles have a Class C (the lowest) fire rating, while fiberglass shingles have a Class A (the highest) rating.

Organic shingles are more flexible in cold weather than fiberglass ones. Some roofers don't like to install fiberglass because they say their stiffness causes them to crack. Manufacturers reply that fiberglass shingles, when installed properly, will last a long time.

The two most common types of asphalt shingle roofing are three-tab, also called a strip shingle, and architectural, also called a laminate shingle.

A three-tab shingle is a rectangular mat with two slots cut in its front edge. The slots provide stress relief as the shingle expands and contracts with the weather. An architectural shingle has a heavy base mat and another mat or sections of mat applied on top of it. Many people like the appearance of architectural shingles. They also are sturdier, but more expensive.

In parts of the country where there's a lot of wind, roofers may prefer T-lock or T-shaped asphalt shingle roofing that is wind-resistant. Roofs with a shallow pitch are often covered with a continuous sheet of asphalt called roll roofing.

Your roofer will probably ask you whether you want a 20-, 25- or 30-year roof in Potrero, California. This often refers to the length of the manufacturer's warranty rather than the quality of the roofing material. Asphalt shingle roofing last about 20 years. After that it is often hard to make a warranty claim stick.