"Most people don't know it but the warranty period (years) is based on the weight of the shingle," said Dana Davis Gudenau, president of Advanced Roofing Technology. "That's because the heavier the shingle the more it can stand up to the UV (ultra-violet) rays.

"But the warranty won't be any good if you don't have proper roof venting. Most people -including some architects - don't know that."

However, Jerry Gudenau, company vice president, says that so far (the past 12 years in Hawaii) there hasn't been any warranty problems from venting.

Homeowners should understand these key issues:

Weight: A typical asphalt shingle with a 20-year warranty will weigh about 203 to 210 pounds per "square" which is the term roofers use for a 10-foot by 10-foot area.

The heavier shingles include Architect 80 by GS Roofing Products Co. at about 280 pounds per square and the Presidential shingle by Celotex at 360 pounds per square. They carry warranties up to 30 and 40 years.

Venting: A roof that "breathes" - such as a wood shake roof put down over wood strips - is cooler than an asphalt roof which is put down over solid plywood panels, says Lyons. "A home with an asphalt roof will be hotter (by about 5 to 10 degrees) and the consumer should know that," says Lyons.

If you don't vent the asphalt roof correctly, moisture will build up from inside, go through the plywood sheathing and eventually rot the felt layer put down over the plywood. Sometime later this moisture will rot the shingle, says Jerry Gudenau.

Roofing manufacturers can supply detailed instructions on how to "balance" the venting of cool air from under the roof eaves and exhausting the hot air on the ridge top, but roofing installers don't really get this kind of detail in their licensing test, he adds.

(The U.S. Department of Housing and Urban Development and Federal Housing Administration recommend a 50-50 balance between vents under eaves and ridge vents; most manufacturers recommend 60 percent under eaves and 40 percent on the ridge. Generally, one square foot of ventilation should be provided for each 150 square feet of horizontal attic space.)

Ridge vents, some made of polypropylene plastic, are the most cost effective way of dealing with moisture, says Jerry. He found that in hot Ewa they can lower the roof temperature by 10 to 20 degrees.

Robert W. H. Rod, senior manager for GS Roofing Products Co. in Hawaii, says the Architect 80 product includes printed venting requirements which follow the FHA minimum property standards.

"In all the years since we came into Hawaii in 1982, we've had no warranty problems because of venting," Rod said. "Architect 80 has gone through the test of time and is now carried by the major (building material) suppliers."

Jim Wilkinson, president of Wilkinson Shake Roofing, agrees that the ridge vent is the best option for asphalt roofs. Installing ridge vents for a new roof will cost about $8 to $10 a lineal foot, and for a retrofit, about $15 to $20 a lineal foot, he says.

A ridge vent involves creating a slot down the ridge of the home so air can circulate. Other options include the spinning turbines, installed for about $150 to $200 each, and the solar-cell powered vents which look like skylights, which cost about $600 installed, says Wilkinson.

You may need only two turbine vents for a typical roof, and maybe only one or two solar vents, he says. But often it is difficult to pin down suppliers on just how many vents are required to uphold the warranty, Wilkinson says.

"You just have to use common sense," he adds. "You have to vent under the eaves to allow cool air to draw in under the roof and you want to vent at the highest point possible (because hot air rises)."

All of these situations are for homes with attics, which trap heat. For homes with open-beam ceilings (no attics), Wilkinson does not advise using an asphalt shingle roof because of heat.

"If the home has black shingles and open beam, some homeowners tell me the home is unliveable," Wilkinson says.

Looking for a cheap solution to heat? Wilkinson suggests putting a puka hose, or drip irrigation hose, on the roof. Turn it on for a short time in the afternoon when the heat buildup is the worst (using a timer if needed). The water will cool off the roof and the house underneath.

Nailing: The manufacturer's recommended nailing pattern is put in with each bundle of shingles. They normally call for three or four nails per shingle, along a certain line. If the installer works too fast with his pneumatic nailer and is not careful, he can get off that line. This makes the shingle more vulnerable to ripping off in a high wind, says Tim Lyons, executive director of the Hawaii Roofing Contractors Association.

Heavier shingles hold up better to winds and can take more nails, without voiding the warranty, says Jerry Gudenau. Don't use more nails on a lighter shingle because that can encourage ripping, says Lyons.

Warranty: Nearly all asphalt shingles carry a warranty of protection to 55 or 60 miles-per-hour winds but the "hurricane shingle" by Malarkey Roofing Co. goes up to 80 miles per hour for homes, says Mark Alexander, the local representative.

The hurricane shingle has both fiberglass and polyester fibers and a modified roofing asphalt which creates a more rubbery, flexible shingle, says Alexander.

The standard protection is five years for wind damage, material defects and labor. However, you must read the details of each warranty. If there are problems, some provide only a prorated return rather than a full return.

Read and compare the fine print, but don't expect a fully paid reroofing job if it doesn't last the full warranty period.

Alexander is not enthusiastic about warranties. "They are for the protection of the manufacturer; it's a sales tool," he says.

Hawaii is hard on roofs because of our year-round hot tropical weather, but Alexander says a well-applied asphalt shingle roof should still last many years here.

While the warranty may not be the complete answer for consumers, Lyons adds: "Asphalt shingles is the area of least complaint (among different types of roofing jobs)."

Other: Shingles with copper granules are better than those with zinc granules in dealing with algae and discoloring, says Jerry Gudenau. Correct decking and sealing are also important.

Avoid nonlicensed roofers and those who offer cheap venting solutions. Wilkinson said that one recent Hawaii scam involved installers who nailed on turbine vents - but without cutting a hole into the roof - so there was no venting at all.

Things that affect the temperature in your attic and house:

MOISTURE: High humidity (40 percent or above) and low outside temperature will cause moisture to accumulate on the underside of the roof sheathing.

THERMAL EFFECT: Result of the difference between air temperature in the attic and outside, combined with the difference in elevation between high and low vent openings. Hot air rises and collects at the peak of the roof.

HEAT: The main source of attic heat is direct sunlight. In an unventilated attic, the temperature will reach 150 degrees or more when it's about 90 degrees outside.