7 Ways to Cool a Flat Roof

A drawback of a flat roof on your home is its tendency to trap heat. Several methods to reduce heat absorption by flat roofs have been developed and proven effective in keeping a home with flat roofing cooler. This can result in noticeable cost savings on air-conditioning your home. Learn more below about these cool roofs and how to make your flat roof reflect heat more efficiently.

Roof Coatings

Specialized roof coatings, in a wide range of materials, can help a flat roof reflect up to 90 percent of solar heat. You can apply these coatings as an elastomeric paint, large polyvinyl chloride (PVC) sheets with heat-sealed seams, or even a thin layer of solar panels that will collect solar energy without increasing the indoor temperature of your home.

Elastomeric Paint

This paint contains an elastomeric polymer that allows it to expand and contract along with the material on which it is applied. Apply two coats of bright white elastomeric paint to your flat roof to increase its solar reflectivity. Tests of heat reduction with elastomeric paint show a 60 to 75 percent improvement in reflectiveness, which translates to dramatic cost savings on energy used for air conditioning.

PVC Sheathing

If you have a structurally sound roof, apply a single-ply PVC sheathing to the entire flat roof surface. Heat-welded seams keep out water and prevent wind damage due to their smooth texture. Reputable manufacturers and installers of PVC sheathing will also help you upgrade your roof in the future with suitable flashings and vents for skylights or fireplace chimneys. The best PVC sheathing is warranted to last 15 years in varying weather conditions. You can also use this sheathing to cover a flat deck over your garage or other rooms in your house, to greatly prolong its useful life.

Solar Photovoltaic Roofing Panels

You can also add ultra-thin solar photovoltaic panels to your flat roof. These will store energy for you to use in your home, and send excess capacity back to the local power grid. When placed over a cool roof laminate of PVC, they will continue to keep your home cool in hot summer weather.

Other Options to Cool Your Flat Roof

1. If you can afford to replace your ceiling, install a layer of solid foam insulation directly under your flat roof. This will keep out both heat and cold, improving your home's energy efficiency.
2. Erect a low-sloped asbestos film shield over the flat roof. It will increase solar reflectivity preventing the roof from absorbing light and heat energy. Ensure you construct it so it will not catch prevailing winds and blow away from the roof.
3. Install windcatchers into the roof to direct cool air downward. Used in countries with hot dry climates for centuries, the windcatcher has an onion-shaped dome with nearly-vertical vanes that will turn in even slight breezes. The vanes force cooler air down a shaft into the house.  A vent seal at the bottom of the windcatcher can be closed and sealed in cool weather to prevent cold air entry.