Are Your Roofs Cool? An Introduction to Cool Roofs.
Occasionally I’m asked to write about some specific green building method or product for real estate investors. Below is a quick outline on Cool Roofs, one of the most effective energy-efficient measures you can implement if you live in the southern half of the US.
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Cool roofs aren’t new, roofing contractors have used cool roofing products for more than 20 years on commercial, industrial, and residential buildings. For real estate investors cool roofs can be a great solution to save energy in any rental property. Since they are so durable and aren’t outlandishly expensive they have a pretty quick payback.
They may be installed on low-slope roofs (such as the flat or gently sloping roofs typically found on commercial, industrial, and office buildings) or the steep-sloped roofs used on many homes.
Some benefits of Cool Roofs:
- Save on annual electricity bills by reducing summer air conditioning costs.
- Save peak electricity demand costs if you have time-of-use metering (usually just commercial properties fall into this category)
- Reduce roof maintenance and replacement expenses by extending roof life.
- Reduce air pollution and smog formation.
- Reduce roofing waste added to landfills.
White vinyl roofs, which are inherently reflective, achieve some of the highest reflectance and emittance measurements of which roofing materials are capable. A roof made of thermoplastic white vinyl, for example, can reflect 80 percent or more of the sun’s rays and emit at least 70% of the solar radiation that the building absorbs. An asphalt roof only reflects between 6 and 26% of solar radiation, resulting in greater heat transfer to the building interior and greater demand for air conditioning – a strain on both operating costs and your wallet.
One of the ways to make an existing or new roof reflective is by applying a solar reflective coating on its surface. These coatings are specially engineered to reflect heat as regular white paint is not enough.
Ceramic coatings are the most well known in this area and they provide an average reflectance of 75% to 85%. Their application is usually done by trained professionals only but any contractor can be shown how to apply these coatings.
High performance nanotechnology heat reflective paints are the most innovative in this field. They can reflect up to almost 95% of solar radiations, reducing a roof’s heat load by an average of 30% in hot weather with as little as 200 microns in thickness (0.2 mm). Working at nanotechnology levels allows thermal barrier paints like Planet Supra, for example, to offer an unlimited choice of colors in matte or glossy finish (the lighter the color, the higher the performance), easy application like any regular water-based paint and additional benefits such as self-cleaning properties thanks to Titanium Dioxide in the formulation.
Although costs will vary greatly depending on location and local circumstances, cool roof coatings on a low-slope roof might cost $0.75–$1.50 per square foot, while single-ply cool roof membrane costs vary from $1.50–$3.00 per square foot. The cost premium for cool roofs versus conventional roofing materials ranges from zero to 5 or 10 cents per square foot for most products, or from 10–20 cents for a built-up roof with a cool coating used in place of smooth asphalt or aluminum coating.
One of the things I like best about cool roofs is that the methodology is simple (coating a roof) yet the technological advances in the product continue to improve. I see this as an emerging trend in residential rehabs as the savings are substantial and the payback is strong.
*Many thanks to my venerable intern, Rebecca Sanders, for her research efforts for this article.