Retrofitting an Existing Roof for Energy Efficiency

The lid of Jeff Wilson's Cape Cod was leaking big time. A new roof bolstered with insulation more than doubles its energy efficiency.

The Wilsons' deteriorating roof actually spearheaded their large-scale Deep Energy Retrofit (DER) project.

Jeff Wilson figured, "If I have to replace the roof, well?" And as home improvement projects go, his ballooned into a full-house energy renovation, including a new home addition.

Raising a Green Roof

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Homeowner and carpenter Jeff Wilson is doing a Deep Energy Retrofit (DER) of his 70-year-old home with the ultimate goal of cutting his energy bill to zero.

That meant retrofitting the existing roof and boosting insulation to reduce the family's cooling costs by up to 17 percent. Plus, by applying new spray-foam insulation, radiant sheathing and eco-smart roofing on top of the existing surface, Jeff didn't fill any dumpsters in the process.

Jeff needed a bigger, more energy efficient roof to connect with a new addition. I-joists (beams made of engineered wood) were nailed into the existing roof to raise the roof angle of the entire back of the house to create a flatter surface to support solar panels.

The "higher" roof created by the I-joists also would allow for a 13-foot ceiling on the addition's second level.

Jeff used Louisiana Pacific engineered lumber, which has a 50-year warranty and is made from small-diameter, fast-regenerating trees. It's much better than using wood from a large tree, plus its bonding elements contain no formaldehyde.

This is a view of the front of the house, showing 2x4s installed as purlins and rafters. Spray-It-Green insulation will fill in the gaps, creating an air-tight surface on which to lay sheathing and roofing material.

Jeff shoots Spray-It Green foam insulation in between beams. He applies about 2 1/2 inches to the front roof and 3 1/2 inches to the back roof, which will support a solar panel system and be roofed with a different material.

Next comes a layer of sheathing. Rather than standard sheathing, Jeff opted for an eco-upgrade: TechShield radiant barrier sheathing from Louisiana Pacific. A shiny, aluminum underlayer on the sheathing faces the house, preventing heat from penetrating into the attic.

In this photo, you can also see the back part of the roof, which was raised with I-joists.

Jeff's team installs radiant sheathing in the same manner traditional oriented strand board (OSB) sheathing is applied: on top of rafters and underneath roofing material.

"That simple layer of aluminum laminated on the underside of the sheathing can reduce attic temperatures by up to 30 degrees and save us up to 17 percent on air conditioning costs," Jeff says.

The steep-sloped roof at the front of the Cape Cod home was shingled with Eco-Star, a recycled rubber product that resembles slate. Its gray color keeps the roof cooler than black asphalt-fiberglass shingles.

The green Eco-Star roofing material has a 50-year warranty and will last up to 75 years. "I'll never have to replace this roof," Jeff says, pleased with his investment. The material costs about three times more than asphalt shingles.

Jeff estimates the energy rating, or R-value, of his front roof is about R-40, and the back roof is near R-50.

Eco-Star roofing is applied in an offset pattern to add character to the front of the home, in keeping with its Cape Cod style. The special treatment cost a few hundred dollars more in labor, but the payoff is an aesthetically appealing surface. "We wanted to make as much of a statement as we could," Jeff says.

The rear dormer roof was covered with Weather Bond Weld-Free TPO, a heavy-duty rubber roof that's thin, stretchy and will work hard to keep heat away from the solar panels Jeff plans to install on them.

"Photovoltaic panels operate best at a moderate temperature, so if the roof heats up to more than 100 degrees, the solar panels lose their efficiency," Jeff explains. "The white shingles will give us a much lower surface temperature, even on a really hot day." And aesthetically speaking, the white rubber roofing is not visible from the curb.

In this photo, you can see the two different energy efficient roofing materials used on the Wilson home: the gray Eco-Star product in the front and the white Weather Bond product in the back. While the products may look mismatched, this doesn't matter since passers-by won't notice the back roof.

But the roof was a priority because the standard fiberglass-asphalt shingles were pushing 30 years. Plus, the previous homeowner splashed white paint on the roof while whitewashing the house, so Jeff covered the mess with gray paint.

Even worse, the black roof was a heat magnet with virtually no insulation underneath. The vented attic below it was leaky, with some basic blown-in cellulose insulation as the only energy-loss deterrent.

"Roofs and ceilings are big energy loss points, and it's a point of thermal gain in the summer," Jeff explains. "With the sun beating on a black roof, the attic heats up, which heats up the rooms below it."

The roof is much more than a lid for your house. It's a primary escape and entry route for warm and cool air. Jeff estimated that the energy rating, or R-value, of the roof was R-19 (a minimum of R-30 is recommended).

Jeff wanted to get the roof as close to R-60 as possible, which meant a completely tight top allowing no hot or cold air transfer between the attic and the outdoors.

Layering on Efficiency

Jeff chose two green products for his roof. For the back of the home, he opted for WeatherBond Pro Weld-Free TPO (thermoplastic polyoletin), a heavy-duty rubber roof that is white to reflect the sun and prevent heat from entering the attic.

The front of the home was roofed with EcoStar recycled rubber material, which resembles slate. It's light-weight, comes with a 50-year warranty, will last about 75 years and is rated well against hail. "You can save money on your insurance by putting this type of roof on as opposed to slate, asphalt or metal shingles," Jeff points out.

Roofing can be a wasteful, messy project when demolition is required. Because the existing roof was dry and intact, the new insulation and roof could be installed directly on top of it, saving a trip to the landfill.

But before roofing was applied, Jeff had some energy-boosting work to do — using spray-foam insulation and efficient sheathing. He fixed I-joists (rafters) made from highly sustainable engineered lumber directly onto the existing roof. Next came Spray-It Green foam insulation, which filled in the gaps. Then he topped this layer with TechShield radiant barrier sheathing from Louisiana Pacific. A shiny, aluminum underlayer on the sheathing faces the house, preventing heat from penetrating into the attic. All this formed a tight foundation for the eco-smart roofing.

"That simple layer of aluminum laminated on the underside of the sheathing can reduce attic temperatures by up to 30 degrees and save us up to 17 percent on air conditioning costs," Jeff says.

The cost of this sheathing is about 50 percent more, but Jeff figures his energy savings will pay off the investment immediately. "This concept of cooler, sealed, conditioned attics can really reduce the cooling load in a home during those hot months," he emphasizes.

Now, Wilson estimates the energy rating of his front roof is about R-40, and the back roof is near R-50.

Green Your Roof

Considering a new roof? This is an excellent opportunity to improve your home's overall efficiency. Jeff offers this advice:

Seek out green products. Look for shingles made from recycled rubber, such as the Eco-Star and Weather Bond Weld-Free TPO products Jeff chose. If possible, opt for a lighter color than asphalt-black. The back of Jeff's home has white roofing, which you can't see from the curbside view. Roofing on the front of the home is gray.

Seal the attic. While replacing the roof, don't ignore the attic ceiling — the ceiling and roof work together to insulate a home. "Aim for that air-sealed attic," Jeff advises, debunking the general assumption that attics must be vented. This is simply not the case, he says.

By sealing the attic, you'll create a more insulated environment for ductwork and prevent heat loss or gain (depending on the weather). Before you seal the attic, though, check the warranty on roofing materials. Some cheaper products will void the warranty if applied on a sealed attic rooftop. "As you move into higher-end materials, you won't find that," Jeff says.

Up your rating. At the very least, shoot for an R-value of 30 for the roof — higher is better. By properly insulating the roof and attic, you can achieve this number.

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