Asphalt shingles are by far the most popular roofing choice. There are two types -- organic and fiberglass. Organic shingles consist of a wood-fiber base that is saturated with asphalt and coated with colored mineral granules. A fiberglass shingle consists of a fiberglass mat, top and bottom layers of asphalt and mineral granules.
One advantage that a fiberglass shingle has over the organic type is fire resistance. Fiberglass has a UL Class A rating while organic shingles have a UL Class C in the Underwriters Laboratories (UL) system for classifying fire resistance. Roofing materials are rated Class A, B or C, with A having the highest resistance to fires originating outside the structure.
Organic or fiberglass, asphalt shingles come in a variety of weights, styles and colors. In general, the thicker and heavier the shingle, the longer it will last. The three-tab shingle is the most common, lightest and least expensive. The architectural grade or layered shingle is heavier, more attractive and pricier.
Wood shingles were once the rage, but their popularity has waned due to concerns about their ability to resist fire.
Remove ALL of the existing roofing down to the space sheathing, repair any damaged framing material and install a solid layer of 3/8" plywood over the existing space sheathing. Then, install roofing paper and your new shingles.
It is also a great time to replace all of the existing roof flashings around pipe, vents and chimneys.