Although we rarely see our own roofs, there certainly are many choices we have to make in choosing a roofing material or color.

In San Francisco, many homes have flat roofs which usually call for traditional tar and gravel while most peaked roof homes typically use composite asphalt shingles.

When replacing a roof or rebuilding one, there are a number of things you should think about that can make a huge difference in the energy efficiency of your home.  Remember that a roof is kind of like a hat and that heat rises.  The roof is not just to keep rain out – it also can work to keep heat in (on cold days) or out (on hot days).

One way to do this is with something called a radiant barrier.

RADIANT BARRIER

A radiant barrier can simply be a metallic sheet or foil that is installed, reflective side up, below the roof, either in or above the rafters or on the floor of the roof above the roof insulation (or both).

The reflective surface reflects heat radiating down from a hot roof back up before it impacts the heat of the house.  The DoE estimates that energy savings could be 25% to 40% in hot weather.  A benefit in cold weather is also possible if there is a barrier reflecting heat back down into the house, above the attic insulation so that when you’re heating the house, the heat doesn’t escape out the roof but rather stays in the house.

Even better is an exciting new coating that is coming down the pike.  It’s just in the lab now and 2-3 years from availability, but researchers have developed a coating that can be applied to shingles to darken them in cold weather to increase the warmth of the roof and lighten the color of the roof in warm weather to reflect more heat.

A great article in Smart Planet suggests that heat gain in color weather could be up to 80% and heat reflection in warm weather could be 50%-80%.  What all this means is that the more effective the roof is at heating up in cold weather and cooling down in warm weather, the less your heating system or air conditioning system has to work.

Less work = less energy use.

Less energy use = more time until our coasts are under water.

Until then, keep your snorkles handy.

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