Photo by James Dulley
The completed metal garage roofing has new flashing and decorative hip trim over the seam.
Q: I want to replace my black, asphalt-shingle roof with one that will last longer and keep my home cooler on hot days. What type of roof do you recommend?
A: If your goal is a long-lasting roof that keeps your home cooler, a black, asphalt-shingle roof is probably the worst option. The dark color absorbs much of the sun’s heat, which not only makes your home hotter and drives up air-conditioning costs, but also shortens the life of the shingle material.
A black shingle can easily reach 150 F in the hot afternoon sun. A square of shingles (100 square feet) can weigh 200 to 350 pounds. When this thermal mass gets hot, it stores the heat and radiates it down into your home, well into the evening.
Even with adequate insulation on the attic floor, radiant heat from the hot roof easily passes through to room ceilings. Standard thermal insulation, such as batts or blown-in fiberglass, rock wool and cellulose, are effective for blocking conductive heat transfer, but less so for radiant heat from a hot roof.
The two most common roofing materials for homes are shingles and metal. White shingles can be fairly energy efficient and effective in reflecting much of the sun’s heat. Because it takes very little color for shingles to start absorbing heat, white is the most efficient option.
Metal roofing can reflect the majority of the sun’s heat. It can also cost twice as much as shingles, but many types have lifetime warranties. Aluminum and steel are the most common and reasonably priced materials. Copper, while quite expensive, is attractive and durable and absorbs heat well. Its natural aged patina is beautiful.
On my own home, I installed an aluminum, simulated-shake roof. It consists of interlocking panels with a special heat-reflecting paint coating. The panels are made of recycled aluminum from soda cans and are formed to look like cedar shakes. After it was installed, our second-floor bedrooms stayed much cooler during summer.
Aluminum is a particularly efficient roofing material, because the underside surface of the roofing panels is bare. Its low-emissivity rating means it emits only low levels of radiant heat, so it doesn’t allow heat from the hot metal to pass through to the roofing lumber and insulation below. Make sure any aluminum roof you select has enough contour to provide an air gap over the sheathing, so its low-emissivity properties will be effective.
One drawback to an aluminum roof is that you must be careful not to damage it by walking on the shakes’ high edges.
Painted steel roofs are also available in many colors and simulated contours. The steel is treated with layers of corrosion-resistant coatings, so rust is not a problem. Steel roofs with an aluminum-alloy coating are particularly durable. Since steel is strong, there are fewer problems with walking on it.
When old shingles crack or develop curled edges, they must be torn off before new shingles are installed. But most metal roofs can be installed over existing shingles, no matter what their condition. This saves the cost (often about $1,000) of tearing off old shingles.
No matter which roof you choose, consider installing an attic ridge vent—a minor additional expense. Be sure soffit vents are not blocked by attic insulation. Even with a metal roof, adequate attic ventilation is needed for both summer and winter energy efficiency.
Companies that offer metal roofs include: Classic Metal Roofing Systems, (800) 543-8938; Conklin Metal Industries, (800) 282-7386; Englert, (800) 364-5378; Gerard, (800) 237-6637; and McElroy Metal, (800) 562-3576.
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