By Cass Jacoby.
Did you know your roof color could be costing you more money to cool your home or office building?
In the summertime we tend to wear light-colored clothes because they keep us cooler since lighter clothes reflect rather than absorb the heat of the sun — it's the same with your roof. A cool roof is often light in color with highly reflective shingles, a type of paint or a sheet covering. While standard roofs can reach temperatures of 150°F or more in the summer sun, a cool roof under the same conditions could stay more than 50°F cooler and save energy and money by using less air conditioning.
Almost any type of building can benefit from a cool roof, so read on to learn the benefits and how to make your roof cooler.
Cool roofs come with significant benefits to the homeowner/ building owner, including:
If you find yourself trying to decide whether or not to install a cool roof, determine if the cost will justify the energy savings. Cool roofs are not necessarily more expensive than a traditional roof, but converting a standard roof in good condition into a cool roof can have an upfront cost. EPA.gov states that the cost premium for cool roofs versus conventional roofing materials ranges from zero to five 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.
Energy.gov suggests calculating energy savings, rebates and incentives, HVAC equipment downsizing and extending your roof life into your final decision on whether or not to install a cool roof. How much energy your cool roof will save depends on several factors, including environment, how well insulated your current roof is, the type of roof you have and the efficiency of your heating and cooling system.
Cool roofs save more energy in warmer climates but can increase energy costs in colder climates due to reduced heat gains in the wintertime. Additionally, consider the humidity of your location because cool roofs can be more susceptible to allergy and mold growth. Some roof coatings include special chemicals that prevent this type of growth for a few years.
You can use this Cool Roof Calculator to estimate cooling and heating savings in your home with a cool roof.
If you are converting an existing roof into a cool roof, you have three options:
1 - Retrofit the roof with specialized heat-reflective material.
2 - Re-cover the roof with a new waterproofing surface (such as tile coating).
3 - Replace the roof with a cool one.
It’s possible to make a new or existing roof cool by choosing the right surface material. Products are available for most roof types, there are many different options depending on your roof type. Find your roof type below for advice on making your roof cool.
Single-ply membranes can be made cool by reformulating or coating black membranes to make them reflective.
Built-up roofs can be made cooler by substituting reflective marble chips or gray slag for dark gravel in a flood coat of asphalt, adding reflective mineral granules or a factory-applied coating rather than a dark coating on a mineral surfaced sheet, or applying a cool coating directly on top of a dark asphaltic emulsion coating.
Modified bitumen sheet membranes can be made cool with a pre-coat of a cool roof coating at the factory.
Spray polyurethane foam (SPF) roofs are usually already reflective and offer cool roof performance.
Shingle roofs can be made cool by purchasing cool asphalt shingles coated with granules that provide better solar reflectance. Coating existing asphalt shingles to make them cool is not normally recommended or approved by shingle manufacturers. Other roof shingles can be coated at the factory or in the field to make them more reflective.
Tile roofs can sometimes be reflective enough to achieve cool roof standards, and adding surface treatments can transform tiles with low solar reflectance into cool roof tiles.
Metal roofs are typically good solar reflectors, but poor thermal emitters, so painting a metal roof can increase its solar reflectance and thermal emittance or you can apply cool reflective coatings.
Have a question? AskARoofer.
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Cass works as a reporter/writer for RoofersCoffeeShop and AskARoofer. When she isn’t writing about roofs, she is writing about movies for her master's degree and dancing with her plants.
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