Sustainable Roofing

Green Roofs
Because the roof is a major component of any building envelope and can impact the environmental footprint of a structure in many ways, it is difficult to evaluate any roofing system without considering ‘green’ aspects. The lifespan of the roof, what the roof is made of and the impact of the roof on the energy efficiency of the building are important factors in the selection of any roof - these are also some of the most basic considerations of any sustainable building system. Add to these considerations the possibility to harvest power or water from the environment, and the roof becomes a powerful tool to reduce the environmental impact of a building.

Things to consider:

Lifespan of the Roof
Some roofing systems, such as slate and some metal roofs, haveserviceable lives that can approach the century mark when properly installed. If installed on a building that will last this long, the impact of keeping multiple short-lived roofs out of the landfill can be significant.

Impact on Energy Efficiency Use of the Structure
Cool roofs are surfaced with materials that reduce the amount of heat from sunlight that is absorbed into the structure. These are often thought of as white or highly reflective roofs. While that is certainly one type of cool roof, there are many others, and not all white or shiny roofs actually perform as cool roofs. It is now possible, for example, to get high quality asphalt shingles of the types that are typically used on residential structures in high albedo or ‘cool’ colors. These shingles do not necessarily look light in color, but are formulated to reflect the sun’s rays back off of the roof.

Living roofs, often called green roofs, can do double duty as cool roofs. Not only do they reduce the Heat Island Effect by reflecting sunlight back, the soil and plant matter add a significant amount of insulation. There are many different living roof systems that are commercially available for buildings and budgets of all sizes.

There are clay and cement tile roofing systems that are designed to incorporate additional insulation above the roof deck. Also, there are many types of radiant barriers designed to be installed below the roof membrane that will reflect heat from the sun back out through the roof. Radiant barriers should be considered part of the roofing systems and compatibility with the roof material should be considered.

Energy Impact to Produce the Roof
There are roofing materials available that are made with a high percentage of recycled content, and roofs that can be recycled rather than discarded in a landfill. In addition to metal roofing and some clay tile roofing, there are roofs made from recycled car tires and other petroleum products that are designed to look like slate and other more traditional roofing materials.

Energy andamp; Rainwater Harvesting
South facing roof surfaces are excellent opportunities to harvest power from the sun. In addition to the rapidly evolving field of traditional photovoltaic and solar thermal systems, there are also solar shingles that are designed to be integrated right into the surface of the roof itself rather than installed above it.

The roof is the primary element of any rainwater harvesting system. In addition to a cistern or collection tank and downspouts, the surface of the roof itself is a consideration. Metal roofs work well, but any roof that will not wash debris such as asphalt granules into the collection tank is a candidate. Many living roofs are designed so that rainwater that is not absorbed by the plants and soil matrix is captured and stored for landscape watering.

Additional Resources
Eco-Structure, a magazine of the American Institute of Architects, discussed sustainable roofing and "what it means to go green on top."

Roofpoint: a rating system for roofs to ensure the use and installation of sustainable materials.