Home Improvement : When Time Comes to Replace Asphalt Roof : Fiberglass shingles last longer, are easier to work with and are lighter than felt type.

Hardly anyone buys a new roof because he wants to. One does so because he is forced into it by an old roof that is wearing out and possibly beginning to leak. When the time comes--about once every 15 years for the average asphalt (or composition) shingle roof--you should certainly make the most of the “opportunity.�

Don’t automatically replace your old shingles with exact copies of the old ones. Spend a little time investigating options that include the actual style and construction of the shingle, as well as colors.

SHINGLE CONSTRUCTION: Asphalt shingles come in two basic types, felt and fiberglass. For years, felt shingles were the only choice. These are composed of a four-layer sandwich. On the bottom is a thin layer of asphalt. Over that goes a layer of organic felt made essentially of very heavy tar paper. Next comes another layer of asphalt to make the shingle waterproof. And on top, goes a layer of colored granules, usually made from ground rock.

In the mid-’70s, technological advances improved the fiberglass shingle. A fiberglass shingle is similar to a standard felt shingle, but it replaces the layer of impregnated felt with a mat of fiberglass.

The fiberglass shingle has a few significant advantages over felt: First, it is more durable, lasts longer and usually has a longer warranty. A standard grade felt shingle is normally good for about 15 years, while a glass shingle should last about 20 or 25. Second, glass shingles are more fire resistant. Third, glass shingles can be lighter and easier to work with. And fourth, they should cost less than felt shingles per year of life.

All this adds up to one simple conclusion. Unless you are concerned only with low initial cost, you should probably consider glass shingles your first choice when you consider replacing a roof.

SHINGLE STYLES: Most of the shingles you see are the traditional three-tab style. These do a good job, but look rather ordinary on your roof. One of the other styles may look better on your home.

The two-tab shingle is similar to the three-tab, but it has two 18-inch tabs rather than three 12-inchers. This de-emphasizes the vertical “bond� lines in the roof in favor of the horizontal “course� lines. This tends to make the roof look longer and lower, and might be a good choice on a roof that seems too square.

Another type, though not a common one, is the no-cut staggered-butt shingle. This design produces even stronger horizontal lines than the two-tab. The staggered cuts in the butts keep the horizontal lines from becoming too pronounced and regular, and give a roof a more distinctive look than tabbed shingles.

Multilayer, multi-tab shingles are made of two layers of roofing cemented together. The top layer has very wide cutouts that give the shingle a pronounced three-dimensional look. They are heavier and more expensive than other shingles, but normally have longer life spans and warranties. Although they cost the most, they offer the most eye appeal. In wood-tone colors, they bear a strong resemblance to wooden shakes. And in gray they create the illusion of slate.

COLORS: Choosing a color is your final option, and it’s pretty much an aesthetic consideration. Color can, however, have a significant influence on the energy efficiency of your home. In the South, where overheating is a problem, white or other light colors are most practical. In the past, white roofs were prone to discoloration from algae growth, but most white shingles today have special granules that resist it.

Whatever color you choose, be sure to select it from actual shingles, not just from printed samples in a catalogue or pamphlet. Also, make sure all your shingles come from the same production run or the color may vary. It also pays to buy an extra bundle or two to keep around the house for repairs in the coming years. Otherwise you may not be able to get a good match when you need it.