The Benefits of a White Roof (or Green)?

We last replaced our roof years ago, when no one was talking about a white roof. But all the recent literature on keeping homes cool assumes smart homeowners or apartment building owners will use a white or light color next time they change the roof. White roofs are difficult to keep clean so we are really talking here about light-colored roofs.

Some would say the house would be harder to heat in winter but this strikes me as wrong. Summer heat can really jack up cooling costs (AC) and if homeowners are worried about keeping their house warm in winter then they should invest in double-paned windows and better insulation. Also, in winter the roof matters less since the sun is coming in from the south wall.

However, it turns out that cutting edge architects and urban planners are less enthralled with white roofs because they simply reflect or redirect light around them. They favor green roofs, as in vegetation! “Vegetation-covered roofs typically include the following layers: a waterproof membrane at the bottom, a layer of drainage materials, a root-repellant and filter layer, a lightweight soil-like growing medium, and finally the plants. Compared to standard roofs, green roofs do have more mass, but thin systems of only 3 to 4 inches (7.5 to 10 centimeters) are sufficient.” (full story here). It is a fascinating idea that can work really well for major buildings but I am not so sure our neighbors are ready for this idea just yet.

By the way, the same arguments apply to driveways – black tar-seal is a heat magnet. We plan to get rid of ours. It is now mostly shaded by trees but on hot days it is impossible to walk on it without footwear.

Photo shows a green roof at the Horniman Museum in London; courtesy of C. Ford (user Secretlondon)/Wikipedia.