Roofs provide one of the most fundamental functions of a building: shelter from the elements. They must endure drastic temperature swings, long-term exposure to ultraviolet (UV) light, high winds, rain, hail and, depending on the climate, snow.
Durability is critical in roofing because a failure can mean serious damage not just to the roof itself but also to the building and its contents. Such damage multiplies the economic and environmental cost of less reliable roofing materials. Most roofing failures take place at joints and penetrations, so it’s not just the roofing material that must be durable but the entire system, including flashings and edge treatments. Proper installation is vital.
Key performance considerations
Roofing can also have a significant impact on cooling loads—within the building and even in the surrounding community.
Use of lighter colored, low-solar absorptance roofing surfaces is one of the key measures advocated in the “Cooling Our Communities” program of the U.S. Environmental Protection Agency.
Reflective roofing can significantly assist appropriate insulation in dramatically reducing summertime solar gain into the building and thereby lowering the cooling load. Roofs with high solar reflectance also help to minimize the “urban heat island” effect, which raises the ambient temperature in urbanized areas.
Alternative materials
Most intriguing environmentally are green roofs (living roofs) in which soil and plantings are used over the waterproof membrane and specialized green roof components. These living layers help replace the ecological functions that are lost when a building footprint covers open land. By using drought-tolerant, low-growing sedums, the planting media requirements with a green roof are fairly minimal. A green roof does not eliminate the need for roof insulation.
Asphalt shingles with fiberglass or organic-fiber mats are still the most common choice for sloped roofing applications. Due to the durability concerns described above, only the heaviest-duty asphalt shingles (with a minimum 30-year warranty) should be considered.
Alternatives are available in steel, plastic, rubber, and fiber-cement that use recycled-content materials and come in shake or shingle styles. Clay and concrete tiles are also an option, especially where hail isn’t a serious threat. Weight is an issue with some of these products. Sheet steel is also increasingly popular on sloped roofs. Steel roofing should have a thick, galvanized or galvalume coating or be factory-coated with a highly durable finish, such as polyvinylidene fluoride (Kynar 500™), for maximum life.
Going solar
The movement to integrate solar electricity generation into buildings—called Building-Integrated Photovoltaics (BIPV)—has reached the roofing industry with the introduction of photovoltaic (PV) shingles and larger integrated roofing panels. These are still quite pricey, and an electrician may have to work with the roofers during installation. Once installed, however, they produce electricity that can help power the building, and any excess can be sold to the utility company in most states.