By MATT MAURY

September in the Pacific Northwest is usually a beautiful time between the seasons. The summer sun that has been baking life out of our homes' roofs is still making frequent appearances. And the winter rains that identify the new leaks in our roofs have yet to begin. It's a great time to enjoy the weather and it's a fine time to prepare for the eventuality of a new roof.

Many people think that re-roofing a home requires only three decisions: type of shingle, color and installed price. However, the elements included in the installed price are the details to which homeowners should pay attention: the construction of valleys, the installation of vents, the replacement of flashing, and the need for a drip-edge. All these elements of a roof should be spelled out in a contract for a new roof.

Roofing material types:

In a drive through local neighborhoods, it's not unusual to see a wide variety of roofing materials - cedar shakes and shingles, tile, metal, even slate and, occasionally, a "hot tar" flat roof. Noticeably, 75-80 percent of the homes have asphalt composition roofs, so that will be the focus of this article.

Composition shingles, sometimes referred to as "three-tab shingles," are made by soaking sheets of material with asphalt, then coating them with small colored granules. Fiberglass reinforcing can be found in the base material of higher quality shingles. While there are no industry standards for defining the life of a shingle, it is fair to say that each manufacturer's "30-year shingle" contains more asphalt than its "20-year" product. the longer-life shingles also are embedded with more mineral granules, which block the sun's ultraviolet rays from causing the shingles to become brittle and crack.

In addition to their traditional roofing, manufacturers have extended their product lines to include laminated and architectural composition shingles. These mix colors and/or thickness to achieve a heavier looking roof.

While composition roofing can be installed over old roofing, it should only be done in cases where the old roof is very flat. Otherwise, the shingle pattern of the old roof will telegraph through the new roof after a few years of exposure to the sun. Never cover an old roof with a new one if there have been leaks which may have caused dry rot or structural damage.

Valley construction:

When two roof surfaces come together to create a valley, it is possible to weave the shingles together to form a channel for rain water runoff. While this may look visually pleasing, it is not the best functionally.

During the winter rains, the amount and velocity of water that runs through the channel increases as it heads to the gutter. This erodes the roofing, knocking the colored granules loose, and increasing the amount of damage that can be done by the next summer's sun. Each year, as the shingles in the valley lose strength, the likelihood of a leak in the roof increases. A preferred material is a metal valley, with a raised "V" running down the center. The metal extends far under the shingles, which are cut uniformly on a diagonal to form a trough for the water runoff. It is important to have the raised "V" in the center because it stops the rainwater from one surface from washing under the shingles on the other surface.

Vent installation:

One of the main functions of roof vents is to remove summer heat and winter moisture from the attic space, thereby lengthening the life of the roofing material. Most roofing manufacturers recommend at least a square foot of venting for every 150 square feet of roof. Half the area vented should be at the soffit level, while the other half should be near the ridge. Spread evenly around the roof, these vents should create a good airflow, with the warmer air escaping from the top while drawing cooler air in at the bottom of the attic area.

Flashing replacement:

When re-roofing a home, flashing should be examined and replaced, as needed. Flashing is generally sheet metal that is put at transition points of a roof and other surfaces to prevent water from getting under the shingles. It is found around dormers, skylights, vents and chimneys. Because a heavy brick chimney is built on its own foundation, it settles independently from a house. Therefore, over the years, the original flashing may crack or pull away from the shingles. That is why leaks around chimneys are frequently found in older homes.

Installing new flashing around chimneys should be done professionally. Roofers are not masons. Take the time to have a masonry firm install flashing correctly before having the re-roofing done.

Drip edges:

At the edge of the roof, shingles will overhang the roof sheathing. A metal drip-edge can be installed beneath the shingles to prevent them from bending and cracking. The type of drip-edge and amount of overhang should be specified prior to work beginning.

The bottom line:

When getting an estimate or writing a contract of a new roof, there's more to think about than just the style, color and price. Besides including specifications for valleys, vents, flashing and drip edges, it is always wise to read the shingle manufacturer's installation instructions and warranties. And, be sure to have the installer's warranty of workmanship included in the contract.

Finally, gutters and downspouts are often replaced at the same time as roofs. If new metal gutters are installed, be sure to use heavy-gauge metal to prevent them from being bent and damaged when a ladder is put against them.

For additional information about gutters, refer to the January 2001 "Around The Home" article on the Seattle Sun Web site: www.theseattlesun.com.