Roofing materials comprise 12 to 15% of construction and demolition waste, and the low-slope roofing most commonly used on commercial buildings is a significant part of this waste stream. Most environmental considerations with commercial roofs are common to roofing in general (discussed in the previous section), with the major local exception of heating and cooling.

The mild climate of the Central Coast is well suited for passive temperature control that reduces and can often eliminate the need for mechanical cooling, and can also reduce winter heating. Few homes in the area are air-conditioned, because operable windows and skylights can easily provide ventilation and cooling for a small building. Larger non-residential buildings can also be effectively cooled without air conditioning in our area, but more careful design is required. Since few local commercial buildings are designed for passive cooling, the financial payback is amplified for roofing that acts to keep summer heat out of the building and reduces cooling loads.

Choose systems that conserve energy by:

• Reflecting sunlight and re-emitting surface heat. Cool roofs can reduce cooling loads and urban heat-island effects while providing longer roof life. However, reflective coatings are not a panacea, particularly if a roof is weathered or in poor condition.
• Resisting the flow of heat from the roof into the interior, whether through insulation, radiant barriers, or both.
• Reducing ambient roof air temperatures through evaporation, as in the case of vegetated green roofs.

Look for non-halogenated roofing membranes (i.e. materials that do not contain bromine or chlorine.) In the event of fire, burning PVC and TPO (thermoplastic olefin) produce strong acids and toxic persistent organic pollution, including dioxin. Protective ballast such as concrete tile may be necessary to comply with fire codes.

Existing PVC and TPO roofing membranes, as well as underlying polystyrene insulation, can sometimes be recycled, and this practice is expected to get more common as Federal construction specification requirements generate increased demand.

Reduce waste, liability and frustration by pursuing roofing with a proven track record, the most durable roofing material that will fit your budget. Some options that are not yet locally common have been extensively tested elsewhere, often in more challenging climates.

Seek materials that can be recycled or reused in the future, reducing waste, pollution, and resource use. Look for options with high post-consumer recycled content - 30% is a good starting point, and the CIWMB Recycled Products Database is an excellent free resource (link below).

Ideally, roofing should renew our natural resources. For example, the potential habitat for birds and native plants on a green roof can be an island of safety in a challenging urban environment, and can help provide pathways for migration through fragmented ecosystems. Similarly, electricity from solar photovoltaic panels displaces demand for fossil fuels. Cool roofing does not renew resources, but is often a highly cost-effective way to conserve them.

Roofing materials are available that provide each of these benefits, but few if any can provide all of them. See the sidebars for information on metal roofing, sprayed polyurethane foam, extended-life asphalt composition shingles, and roofing made from recycled rubber or plastics.

Green materials databases that can connect you to environmentally preferable roofing: