Choices affect costs in keeping a home coolBy James Dulley
When you consider color and materials, a black asphalt shingle roof is probably the worst option for a home. The dark color absorbs much of the sun’s heat, which makes a home hotter, drives up air-conditioning costs, and hastens the degradation of the shingle material itself.
Black shingles can easily reach 150 degrees Fahrenheit on a hot afternoon. They are heavy, and when this thermal mass gets hot it stores the heat and radiates it down into your home well into the evening.
Shingles and metal options
The two most common roofing materials for homes are shingles and metal. White shingles can be fairly energy efficient and effective for reflecting much of the sun’s heat. It takes very little color tint before shingles start to absorb heat, so white is the most efficient option.
Metal roofing can cost twice as much as shingles, but many types have lifetime warranties, and they can reflect the majority of the sun’s heat. Aluminum and steel are the two most common and reasonably priced materials. Copper is attractive and durable. It is quite expensive, but the natural aged patina color is beautiful and it absorbs heat well.
Aluminum is a particularly efficient roofing material because the underside surface of the roofing panels is bare. With a low emissivity rating, it does not allow the heat from the hot metal to pass through to the roofing lumber and insulation below. When selecting an aluminum roof, it is important that its contour provides an air gap over the sheathing for its low-emissivity properties to be effective. A simulated clay tile aluminum roof is also very effective with the many air gaps under it.
Two drawbacks to an aluminum roof: you must be careful walking on it and stepping on the high shake’s edges so it is not damaged, and, during winter, snow can slide off in large sheets. Snow stops can be glued to the roof, but they may also catch leaves and debris.
Painted steel roofs are available in many colors and simulated contours. The steel is treated with many layers of corrosion-resistant coatings so rust is not a problem.
Steel roofs with an aluminum-alloy coating are particularly durable. Steel is very strong, so there are fewer problems with walking on it.
If you have old, asphalt shingles, they may have to be torn off before new shingles are installed. However, most metal roofs, because of their rigidity, can be installed over existing shingles no matter what their condition. This saves the cost, about $1,000, of tearing off the old shingles.
Whether you choose white shingles or a metal roof with heat-reflecting paint, consider installing an attic ridge vent (a relatively minor expense). Make sure the soffit vents are not blocked by attic insulation. Adequate attic ventilation is needed for both summer and winter energy efficiency.