Keeping It Cool: Roofing Options

November 22, 2013 by Taylor Studios in Professional & Industry Tips

I’m going to continue my green building theme by writing about roofing options that can lower your cooling costs. I am not going to cover what is considered a truly “green roof,” the planted kind, because there’s enough info there for a whole post. Stay tuned for that episode. Even without including a green roof, there are a lot of options for both homeowners and business owners that will cut your cooling bill. Trying to find consistent figures for how well various roofing materials cool your roof is very difficult, since manufacturers always manage to find data that supports their particular product. If you want to dive into some juicy data, try this from the Florida Solar Energy Center. What everyone does agree on is that a roof that reflects solar radiation has big effects. A dark shingle roof absorbs heat, which moves into the building below and increases the load on AC units. A dark roof, after absorbing the solar radiation, emits heat into the air above it, increasing the air temperature and adding to the .

Flat Roof Options

Many commercial buildings have a flat or slightly sloped roof. One of the most common flat roof coverings is the built-up roof, or tar and gravel roof. This covering is made of at least four alternating layers of tar and a , either glass fiber or organic mats. If the top layer includes white-colored gravel, it can reflect quite a bit of heat. However, the very roughness of gravel scatters a lot of light and infrared instead of sending it back skyward, which cuts down on how cool it can really be.

Roofing membranes have been used since the 1960s, mostly EPDM rubber membranes. Sold in several different thicknesses and widths, membranes are sold in rolls that are laid out and cut to size on site by the installation crew. An important note is that without a reflective top layer, these roofs lose most of their cooling ability. Yes, they should be installed over some sort of insulation layer, but if that dark gray membrane roof is 50 degrees warmer than the air temperature on a summer day, that heat load can overcome the insulation benefit quickly.

There are , such as EPDM rubber, TPO, and PVC sheet, each formulated differently. One important aspect of membrane roofs is how seams are sealed, since the seams fail long before the membrane. Seams sealed with adhesives may be more prone to failure or weather damage than those sealed mechanically or with hot air welding. While the price point of one membrane may be a lot lower than another, you may only be buying problems down the line, so do your homework!

One more cool flat roof option is an . This isn’t a roofing system, it’s a white coating applied on top of a current dark roof that greatly increases reflectivity. It also extends the life of the original roof membrane. I would consider this more of a cheap fix than a roofing solution.

Sloped Roof Options

Sloped roofs are much more common on homes, and I doubt any of these choices will surprise you. Asphalt shingles, while the most common and least expensive material, absorb a lot of heat and are offered in many dark shades that only increase the heat of the roof. Almost anything is cooler than asphalt shingles. Tile roofs, while rare in the Midwest, are a smart, cool choice in the warmer (read: above-freezing-in-winter) parts of the country. Extremely long lasting, tile roofs can be cast using pale clays to increase reflectivity. Their curved shape helps with ventilation, and their significant thermal mass can keep the home cool during a blazing hot day.

Metal roofs are a common sight in rural areas due to their use on pole buildings and newer barns. These standing seam roofs (named after the vertical seams running between each sheet) are long lasting and tough. Since they can be painted with special solar reflective paint, standing seam roofs can reflect a lot of the sun’s heat, while the metal itself reflects a lot of the infrared. If you would like a more conventional looking roof, you can also use metal shakes, shingles, or tiles. These have all the toughness of a standing seam roof, but are much less obvious. Since pale roofs are not always preferred, manufacturers have started to develop that look dark to the human eye, but can reflect up to 60% of the sun’s radiation (including UV).

When we are due for a roof upgrade at our offices or our production building, I know we will be opting for the coolest roof we can afford. It only makes sense, since HVAC is one of the biggest energy costs for any business. Have you or your business made a cool roof investment? It would be great to get your feedback!