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My small town on the outer edge of the Denver metro area is beginning to experience a push for more housing — particularly for affordable housing. This is driving developers to construct dense multi-family apartments and condos on vacant lots and on clusters of what would have been single-family home lots. There is much concern about the increased density — noise, traffic, aesthetics, change, etc. However, increased urban and suburban densities has both pros and cons. Transportation options, for example, increase with greater density, as does housing affordability. I’m not opposed to development, as long as it’s done thoughtfully.

One often unnoticed issue with greater density is the loss of natural spaces. If you replace a single-family home with apartments or duplexes, there is also usually a transition from yards and vegetation to more, usually flat, rooftops and paved parking lots. The urban heat island effect is well-documented, but that’s not the only impact. The change in albedo (solar reflection) increases surrounding temperatures. The loss of vegetation increases pollution, since the vegetation is not collecting dust or removing aerosol contaminants or producing more oxygen.

There has been much research and testing done to explore solutions to the effects of increased building densities. I categorize them as solar, green and white.

Solar panels can be used on rooftops to produce energy from the sunlight, and are becoming more cost competitive, efficient and practical. Governments and power companies are getting on the bandwagon to support and, in some cases, subsidize residential solar panels. Not all roofs can accommodate solar panels (our house is flanked on the south and west by large trees and the solar salesperson suggested we cut them down to give us the necessary roof space for functional solar panels. We checked our priorities and then declined.) Newer technologies include solar roof tiles that can replace normal shingles.

Green roofs, partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane, can be used to fight urban heating, provide environments for insects and birds, grow vegetable or flowers, reduce runoff, capture carbon dioxide and generate oxygen. They can also provide an aesthetic benefit to both building users and surrounding observers. Vegetation technologies are being explored that grow plants on roofs and walls with a minimum of growth substrate (soil), including the idea of moss-type plants that would grow on shingles, not unlike the thatch-roofs of the English countryside. One summer near Fairbanks. I witnessed a man mowing his sod-roofed cabin.

The use of black tar or tar paper as a sealant on flat roofs creates a perfect heat island generator. In order to fight the urban heating effect, a few communities have tried, with some success, to require the roofs of commercial buildings be painted white to reflect, rather than absorb, the sun’s heat.

Damien Carrington reports, “White-painted roofs have been used to cool buildings for centuries … Currently available reflective white paints are far better than dark roofing materials, but only reflect 80 – 90% of sunlight and absorb UV light. This means they cannot cool surfaces below ambient temperatures.”

However, “The whitest-ever paint has been produced by academic researchers, with the aim of boosting the cooling of buildings and tackling the climate crisis … The new paint reflects 98% of sunlight as well as radiating infrared heat through the atmosphere into space. In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight.”

Human innovation is just getting focused on our roofs, and I expect it won’t be too long until we have even more really positive choices.

“Solar, green or white?”

Additional information:

Damian Carrington, Whitest-ever Paint Could Help Cool Heating Earth, Study Shows, 15 Apr 2021, The Guardian