Affordable Housing Smart Roof Report

Project Description

The last decade has seen the emergence of a range of rooftop technologies that provide important health, energy, water, and environmental benefits. These technologies include: cool roofs; green roofs; rooftop solar photovoltaics (PV); and solar hot water. Impacts from the deployment of these technologies on affordable housing, in areas with low average income, or city-wide could be transformative for quality of life during the summer months, sharply cut energy bills, improve the quality of local waterbodies, and help slow climate change cost-effectively.

These benefits, which include reduced risk of mortality as well as improved air quality and lower energy bills are felt the most in buildings and areas of a city with high concentrations of low-income residents. Energy bills are typically higher in lower income multifamily units in part because there are fewer energy efficiency features compared to higher income multifamily units. Energy costs also make up a higher percentage of expenses for low-income residents. As a consequence, the impact of energy bill reductions is proportionally larger for affordable housing properties. Furthermore, affordable housing is commonly located in areas with higher summer temperatures due to the urban heat island effect, poor air quality, and greater population density. These characteristics generally make affordable housing properties and areas of low average income the most important areas to focus on for installing cool roofs, green roofs, rooftop solar PV, and solar hot water.

The report below presents a conservative estimate of the costs and benefits of applying these technologies on a multi-unit affordable housing property in each of four US cities: Washington, DC; Philadelphia; Baltimore; and Los Angeles. Data for these properties were provided by the National Housing Trust and Enterprise Community Partners. The report demonstrates that, in general, cool roofs, rooftop solar PV, and solar hot water are cost-effective retrofit options for the properties evaluated and that these technologies bring both substantial benefits to tenants as well as broader benefits to the community and city. Given the current set of benefits estimated, green roofs retrofits are only cost-effective on the Washington, DC property.

The report presents the first rigorous and fairly comprehensive model to estimate the costs and benefits of cool roofs, green roofs, rooftop PV, and solar hot water for affordable housing developments. It has involved a range of leading health and policy advisors and the development of a multi-level health and benefits valuation model to quantify a significant set of costs and benefits of these technologies on affordable housing developments. The report’s methodology provides a powerful platform to understand and address affordable housing roof design opportunities. This report’s findings also suggest that a low income area-wide strategy of adoption of the technologies analyzed would likely have large benefits, including providing significant energy savings, reducing area-wide peak summer temperature, improving livability, and providing large public health benefits.

Project Summary Deck
Project Report

If after reading the Report you are interested in reading the Appendix (which is not as well written!), please email us at


“NHT is proud to be a partner in developing this important analysis. The findings—that green, cool and solar roofs can have large financial, health, and environmental benefits—have broad and important implications for the larger affordable housing community, and U.S. cities as a whole. The report is a milestone because for the first time it provides a rigorous and complete cost-benefit analysis that enables housing owners to make efficient use of their roofs, which ultimately strengthens their overall properties and helps them achieve and maintain affordability.”
Michael Bodaken, President of NHT
“Past research shows that ‘smart’ roof strategies that reduce extreme temperatures in buildings can literally save lives. This new report provides additional justification for cool, green, and solar roofing solutions by showing that they also make compelling financial sense as we work to make DC a healthier and more sustainable city.”
Tommy Wells, Director of DDOE

Funded by

The JPB Foundation