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

See All Photos

Shop This Look

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.

Next Up

Why R-Values Matter in Energy Efficiency

R-value measures the ability to prevent the transfer of heat; the larger the number, the harder that insulation is working at preventing heat conduction.

Repel the Sun's Heat With Radiant Sheathing

Improve energy efficiency by putting insulation beneath roofing material.

Energy Answers: The Reason for Retrofitting

A passion for energy efficiency leads to a serious retrofitting commitment.

The Benefits of Deep Energy Retrofits

Take energy conservation to an extreme with upgrades that go far beyond simple weatherization.

How to Build Airtight Insulated Cathedral Ceilings

Proper construction techniques can help ensure airtight, dry and energy-efficient cathedral ceilings.

Home-Energy Audit Saves Money

Find out how a professional inspection can reduce a home's energy use and utility bills.

Replacing Leaky Windows

Energy-conscious carpenters trades old windows and doors for more sophisticated, airtight alternatives.

Building an Energy Efficient Home Addition

A homeowner makes sure his retrofit of his 70-year-old home addition saves energy.

Air Sealing a Drafty House

Learn techniques to more than double your home walls' energy-efficiency rating.

More from:

Energy Answers

Go Shopping

Get product recommendations from HGTV editors, plus can’t-miss sales and deals.


Follow Us Everywhere

Join the party! Don't miss HGTV in your favorite social media feeds.