By Will Driscoll
People who sleep in a top-floor bedroom under a black tar roof are likely to lose sleep on summer nights due to radiant heat from the roof, with serious health consequences. Such roofs are common on older Northeast urban row houses (also called townhouses).
Technically, the fix is simple—coat every black tar roof with a white coating—but progress toward that goal is slow. A new public health measure to require cool roof coating could help prevent sleep deprivation and its consequences.
The issue: black tar roofs get really hot, keeping people from sleeping well, and causing real problems
Black tar roofs “can reach temperatures of 150°F or more in the summer sun,” reports the U.S. Department of Energy. With or without air conditioning, a roof that hot above your bedroom will radiate heat at you all night long.
And people can’t sleep well when it’s too hot. A research study using data reported by 765,000 people over 10 years found that “increases in nighttime temperatures amplify self-reported nights of insufficient sleep.”
Losing sleep is far worse than a nuisance. “People make cognitive errors that matter when they sleep badly, whether crashing vehicles or making poor decisions in the workplace,” said UC Berkeley professor Solomon Hsiang in response to the study, as reported by Bloomberg. He added, “Students learn poorly when they don’t sleep, and consistent lack of sleep harms people’s health.”
The technically easy solution: white roof coating of tar roofs
Any roofing firm can apply an “elastomeric” white roof coating to a black tar roof, which can reduce a roof’s temperature on a 90-degree day from 150°F to 95°F. (“Elastomeric” means a coating that stretches with the roof as it expands when it’s warm, and contracts with the roof when it’s cold.) A homeowner who can safely get up on their own roof, with tools and supplies, can also do the job. The cost is modest, since the job is relatively small: clean, patch, prime, and apply the finish coat.
But progress is slow in getting black tar roofs coated white. In Philadelphia, for example, where people have been talking about this issue for a decade, look closely at the Google Maps satellite view of the city and you will see mostly black roofs, while the roofs that aren’t black are generally gray—a color that provides only about half the cooling benefit of a white roof.
A public health measure can help prevent sleep deprivation due to hot roofs over bedrooms
Landlords who don’t pay their tenants’ air conditioning bills have no incentive to apply a white roof coating to their properties, and thus improve their tenants’ health. Cities with black tar roofs could institute a public health measure requiring that bedroom ceilings not exceed a certain maximum temperature, with a presumption that houses with black tar roofs fail that standard. Then, if a landlord did not meet the standard—either by coating the roof white or showing that the bedroom ceilings do not get too hot in the summer—the city could coat the roof white and bill the landlord via the property tax bill.