Roof Energy Efficiency Guide

Roof Energy Efficiency Guide

T he key job of a roof is to keep water out. But it should also be energy efficient, and that means that the roof should also keep the heat out of our homes. Yes: keep the heat out even in cold climates.

Roofs cant ever be a significant source of useful heat gains. In cold climates, attics have to be properly insulated to prevent heat loss during the heating season; and that and the need of protecting the house from the summers sun, make it impossible to get useful heat gains from the roof in the heating since. Hence the other major function of roofs, besides keeping the water out: to keep the heat out of our homes, in hot weather. Thats important to reduce air conditioning costs.

Keep Roofs Cool by Using a Mix of Strategies

Its difficult to keep the heat out of the attic and home, in hot weather. A single measure may not be sufficient.

Consider the best combination, taking into account your climate and the different roof cooling techniques: 1) shading the roof with trees, 2) using reflective roofing materials and reflective coatings, 3) using radiant barriers under the roof, 4) using roof ventilation and 5) using attic insulation

Radiant Barriers Are Inexpensive and Easy to Apply to Roofs

Radiant barriers are one of the most effective techniques for roof cooling, namely in hot and moderate climates. They are lightweight, clean, non-toxic and easy to handle and to install.

But you should not install radiant barriers on the attic floor, over existing ceiling insulation. They should be applied to the underside of the rafters.

Roof Ventilation Is Important, But Attic Ventilation Fans May Be Ineffective

Roof ventilation can help keep attic temperatures lower. Just do not overestimate its importance, and do not increase ventilation beyond the necessary. And be cautious with attic ventilation fans; they can be very ineffective.

Light-colored roofs are great for roof reflectivity and to keep the attic cool in the summer. But it depends also on the type of material: metal roofing and clay tiles are better than asphalt shingles

Membranes for Flat Roofs

Poly-iso and other spray foams are excellent choices for flat roofs that aren’t visible from the ground. They are very durable and do not leak. But their yellow color is not attractive.

Plastic and rubberized membranes like EPDM (Ethylene Propylene Diene Monomer) are more popular, and are energy-efficient choices. White EPDM rubber membranes provide very high levels of reflectivity (80%).

Attic ventilation is critical to reduce heat loss in winter and to reduce solar heat gains in hot weather. Consider very high levels of attic insulation, and air seal the attic before installing any insulation.

Roofing Coatings Are Inexpensive but May Not Be Compatible with Existing Roofing Materials

Reflective roofing coatings can make a big difference, in existing roofs. They are excellent to prevent overheating. Materials like acrylic elastomeric coatings are easy to install on many existing roofing materials, and will extend their life.

The problem with them is that they are not compatible or effective with asphalt shingles and other common types of roofing materials.

Roofs Should Be Durable to Be Eco-Friendly

Exposed to sunlight, rain, wind and other elements, many asphalt shingle roofs do not last more than 20 years; and thats too short.

Choose a durable roof. And consider eco-friendly features. There are dozens of companies recycling car tires, plastic and metal into roofing materials. And some of these recycled roofing materials can be durable

Shade Your Roof, If Possible

Shade your roof, if possible. One or two big trees, properly located, can make a big difference. Thats one of the most effective measures for blocking solar heat through roofs, walls and windows. Pay attention to landscaping.

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