Single-ply membranes, such as EPDM, are ideal for large roofs with few penetrations and no foot traffic or heavy equipment. (Photo courtesy of Gooding, Simpson & Mackes, Inc.)

Gary Houck, president and CEO of Harrisburg-based Houck Services, Inc., says, "You have to ask yourself what the real intention of the building is. Are you looking for insulation value? Are you planning to get the most number of years you can out of the roof, or are you going to sell the building in a few years?"

Fox says roofing is classified in two categories: "steep slope," which has a 3 to 12 pitch, or slant, and "low slope," which has less than 3 to 12 pitch.

Steep slope systems usually incorporate natural slate, clay tile, cement shingles, metal, asphalt, or fiberglass/asphalt shingles and are best suited for churches, schools, and small office buildings.

Low-slope systems include "built-up roofs," which use several layers of felts with coal tar and are suited for large distribution and manufacturing buildings or those on which there is a lot of foot traffic.

Other low-slope systems include single-ply membranes, such as ethylene-propylene- dieneterpolymer (EPDM), which is widely used in the northeastern U.S. and is ideal for large roofs with few penetrations because it can be supplied in large sheets. Polyvinyl chloride (PVC) is another single-ply membrane, but it is more durable and chemical-resistant than EPDM.

Houck says EPDM can be adhered to the roof decking with glue or hot bitumen or mechanically attached with screws. He says EPDM is the least expensive roofing system.

But if there is going to be a lot of foot traffic or heavy equipment on the roof, it's best to avoid rubber roofs, warns John Dorfler, president of the Ephrata roofing firm Gooding, Simpson & Mackes, Inc. "A lot of architects love rubber roofing, but if there are people walking on the roof frequently checking on equipment, such as the heating, ventilation, and air-conditioning units, that's hard on a rubber roof," he says.

Houck says metal roofs are popular when aesthetics are important. Mansard roofs are commonly made of metal, for instance. He says that although metal is expensive it is "there for a long time" and rarely requires maintenance.

Metal roofs offer another bonus in today's "green-oriented" society, says Dorfler. "There are virtually no environmental issues with metal roofs," he says. Another green trend is in rubber roofing, he says. Historically, the adhesives used were solvent-based, which was detrimental not only to the environment but also to the installer. Now more contractors are utilizing water-based adhesives. He says one solvent-free membrane, thermoplastic olefin (TPO), is new to the U.S. market but is popular in Europe. Sheets of TPO are heat-welded and melted together, says Kirby Sensenig, secretary of Ephrata, PA's Richard L. Sensenig Co. "TPO is slightly more expensive than a rubber roof, but it is economical because it's white and it reflects heat," Sensenig says.

Preventative maintenance is the key to avoiding aggravating roofing problems later, say Sensenig, Houck and Dorfler. "I can't stress enough the importance of maintenance," says Houck. "Maintenance should be done by a professional roofing contractor with a proven track record." He says a detail-oriented roofing professional will inspect the roof for leaks, damage, insulation problems, and the condition of the flashing, edging and work around penetrations. Dorfler recommends having a professional check for signs of damage twice yearly and specifically after major weather events, such as significant snowfall or tornadoes.

Another vital piece of advice: "Stay with proven products," says Sensenig. He notes that with so many new roofing products hitting the market, it's easy to be attracted to fancy marketing gimmicks. "There are lots of new systems, but we don't use any until they're tried and true," he says. "If we tried every new product on the market that wasn't proven to be effective and reliable, our reputation would suffer."