Can painting your house white keep it cooler?
As we live through the punishing heat of worse-than-usual weather, we believe this is a very timely topic. (I refrained from saying it’s a “hot topic” because . . . well, it was just too easy.)
Anyone who’s gotten into a black car on a 100-degree day and wished they’d bought the silver model instead may have wondered if the same principle applies to houses. Does white paint help cool your home as well?? We spoke to Audrey McGarrell of the Cool Roof Rating Council to find out.
The Cool Roof Rating Council
PM: Can you tell us about the CRRC and what they do?
AM: The Cool Roof Rating Council (CRRC) is a 501(c)(3) nonprofit that maintains free, publicly available directories of the radiative properties (solar reflectance and thermal emittance) of roofing and exterior wall products. We also conduct technical research and education on how cool roofs and exterior walls can help improve building performance, increase occupant comfort, mitigate the urban heat island effect, and reduce greenhouse gas emissions.
Our mission is to bring objective, scientific information related to cool surfaces to critical discussions and informed decisions about the impacts of heat islands, extreme heat, and energy use in the built environment.
PM: So you’re evaluating the cooling properties of roofing and exterior products such as paint. How do your ratings get calculated?
AM: CRRC ratings have strict requirements that were developed by a diverse group of subject matter experts. When a manufacturer wants to get a particular product rated, they obtain testing from an accredited independent testing laboratory that is approved by the CRRC, or sometimes a manufacturer’s own R&D lab if they’ve completed a rigorous approval process and demonstrate ongoing compliance with our protocols.
Test results come directly to the CRRC from the test lab, and the CRRC reviews them as an unbiased third party. They’re then published on our Directory.
And we go even further. Test specimens are sent to an approved test farm where they are exposed to the elements for three years and then returned to the independent test lab for what we call “aged testing”. The aged results are a good indication of how the product will perform over time. These results are also published on the Directory.
The Cooling Properties of Paint
PM: What most affects how well a particular paint performs? Why exactly does white paint help keep your home cool?
AM: The surface radiative properties of paint (its solar reflectance or “SR”) and its thermal emittance (“TE”) affect how much solar radiation enters a home as heat, and how efficiently heat is radiated away from the building. The radiative properties are measured on a scale of zero to one, with one being the most reflective or emissive. White or light paints perform well on both these factors.
Of these two properties, SR has the most drastic effect on how cool your home stays. This is because products with high SR will prevent a greater portion of the sun’s heat from entering the building, by reflecting it away. TE is also important because inevitably, some amount of heat will be absorbed by the wall surface. High TE allows the surface to efficiently re-radiate the absorbed heat back into the atmosphere.
In paints, the component that has the greatest effect on a product’s SR is the pigment. Lighter pigments inherently have a higher SR, while darker pigments have lower SR. There are also pigments that are specially designed to be highly reflective of infrared waves while maintaining a darker visible color.
Effect of White or Light Paint on your Energy Bill
PM: To what degree (no pun intended) does this have a real effect on your cooling bill? Does white paint help cool your home in a tangible way, or is it more of a psychological effect? Is there a way to quantify how much this will help a homeowner?
AM: Cool exterior walls are demonstrated to save energy in the southern half of the U.S. and California. The exact energy savings for a given home depends on several factors, including the home’s age, wall insulation and assembly, climate, orientation of the building, and the efficiency of the home’s HVAC system.
However, a study published by the California Energy Commission in 2019 confirmed that in warm states including Texas, cool exterior walls “reduced whole-building annual HVAC energy use 2.0 percent to 8.5 percent in single-family homes.” According to the study, this “lower[s] annual energy cost intensity $0.1/square meter to $1.1/square meter in single-family homes.”
PM: I love that it’s quantifiable! Sounds like solid confirmation to those of us who wondered, can painting your home white keep it cooler. But what if someone doesn’t want to paint their home white or in a light color?
AM: White, off-white, and pastel paints are inherently more reflective at no additional cost to the consumer. However, if you prefer darker colors, there are other options available. Some paints on the market use infrared-reflective pigments that have a darker visible color but a higher solar reflectance than their conventional counterparts. Since these pigments are more expensive to produce, there is a slight cost premium for these kinds of paints. However, these additional costs can be recovered through energy savings in a home with air-conditioning.
“In warm states including Texas, cool exterior walls reduced whole-building annual HVAC energy use 2.0 percent to 8.5 percent in single-family homes.”
The Urban Heat Island Effect
PM: So it looks like not only does white paint help cool your home, but so does any pale color, and even darker colors that have infrared-reflective pigments. Are there other factors to consider? What about the “urban heat island” effect?
AM: The urban heat island (UHI) effect is a phenomenon in which cities are several degrees hotter than their surrounding suburban and rural areas during the day and at night. This is caused by a high concentration of surfaces such as roads, parking lots, roofs, and walls that absorb the sun’s heat, coupled with tall buildings that block or slow air movement. Waste heat released by vehicles and A/C units and a lack of trees and green space make it even worse.
The UHI effect poses a threat to our health because heat is the leading weather-related killer, and heat illness and fatalities have a disproportionate impact on low income neighborhoods, communities of color, and older adults. Heat also causes an increase in ground level ozone, which is a dangerous pollutant and a key component of smog. For all of these reasons, it is important to use every tool in our toolbox to help reduce UHIs and keep our homes cooler.
So there are tangible benefits, beyond just the effect on one’s own energy bill, to painting homes – and commercial buildings – in light, heat-reflective colors.
Yes, homeowners can be pretty confident that repainting with any light-colored paint will help them save on energy bills to some degree. Painting your house white or a light color can keep it cooler, and that’s definitely a benefit in terms of both comfort and budget. But this is also a topic of interest to urban planners, and to architects and builders as well, especially if they’re pursuing LEED certification and specifying roofing as well as paint selections.
Thank you so much for all this practical and detailed information! If anyone has additional questions, we’ll post contact info below.
Absolutely. We would love to chat with anyone that has questions about cool exterior walls and the CRRC Directory!
How to Contact the CRRC
If you’re ready to paint your own home in a lighter shade, bear these four factors in mind when picking an exterior paint color. Don’t make the mistake of picking too bright a white! You’ll still have the cooling effect of a light color when selecting a “white” that is one or two steps down from the brightest color on the paint store’s color strip. Hire a color consultant if you want some help, and enjoy the practical benefits of beautifying your home!