Cool roofs are a hot topic in energy efficiency and green building circles.Temperatures on a dark-colored asphalt roof in the NYC area can reach 150 to 175 degrees on a hot summer day.
- The temperature outside may be 95 degrees, which is plenty hot, but your roof is conducting a much higher temperature down at you and your family, making the rooms below hotter and making the air conditioner work harder.
- Plus conventional dark roofs retain the heat, contributing to the heat island effect in urban areas, and cooking your house well after the sun goes down.
- A cool roof, on the other hand, can be 50 to 60 degrees cooler than a conventional dark-colored roof.
You will benefit several ways by moving away from the Dark Side and making your roof a cool roof:
- You will reduce the cooling load on your home, save energy, and reduce utility costs.
- By reducing the solar gain and heat retention, you also increase comfort in your home.
- You will reduce the heat island effect caused by your home's dark roof.
You do not necessarily have to paint your roof white, but it must be reflective. There are darker color paints and other materials with reflective properties that may be more aesthetically pleasing.
A must for anyone looking into cool roofs is the Cool Roof Rating Council website. Check out the CRRC's Rated Products Directory that provides performance data about roofing products. How much reflectance does the product have on a 0-1 scale? The higher the number, the more reflectance.
- The CRRC's Rated Products Directory is great for comparing different roofing products, and the ratings come from independent testing, not manufacturers' claims. That is an important distinction.
- It also gives the product an "aged rating," which tells you how the product performed after 3 years of weather exposure.
- Look for a product with a good initial rating and make sure it was still performing well in the testing after 3 years.
In California the building code defines a cool roof as "Any roofing product with an initial thermal emittance (ability to radiate heat) greater than or equal to 0.75 and a minimum initial solar reflectance of 0.70."
Check the cool roof program guidelines in the NYC program to see what the requirements are for your area, then find products that would meet those requirements on the CRRC website. There's plenty of other cool info on the CRRC website, too.
For more information:
Read Susan Wisniewski's Q&A "What's the difference between a green roof and a white roof?"
Also check Paul Gleicher's Q&A "I'd like to know more about on-site wastewater treatment and green roofs in NYC. Can you help?"