How Many Hours-of-Safety Do Our Homes Have in Extreme Weather?

The briefing introduces 'hours-of-safety' to measure how long a home remains at a comfortable temperature after power is lost during extreme weather. It highlights the life-threatening risks of heat waves and polar vortexes, particularly for vulnerable populations in poorly insulated housing. The author advocates for passive design strategies—such as improved insulation, tighter envelopes, and cool roofs—combined with islandable solar PV and battery storage to increase passive survivability and community resilience.

• The author proposes the concept of 'hours-of-safety' to quantify the duration a home can maintain a comfortable indoor temperature before it matches extreme outdoor conditions during a power outage, noting that the difference between 5 and 20 hours can be critical for the survival of vulnerable populations.
• Extreme weather events are increasing in frequency and magnitude, with the National Resource Defense Council projecting nearly 30,000 annual heat-related deaths in the United States by 2100 if carbon dioxide emissions persist at current levels.
• Power outages during extreme weather are a significant risk; between January and June 2019, severe weather caused over 2.9 million customers to lose power for a combined total of 684 hours.
• Passive survivability—the ability of a building to remain livable without electricity, water, or fuel—is primarily determined by the home's insulation and air leakage. Effective strategies to increase hours-of-safety include tighter envelopes, thicker walls, cool roofs, lower window-to-wall ratios, and natural ventilation.
• In warm climates, applying white paint can reduce roof temperatures by up to 30°C (86°F) and indoor temperatures by 3.6°F to 9°F. Additionally, combining an efficient building envelope with battery storage and islandable solar PV systems can maintain power during outages.

APA

RMI (2019). How Many Hours-of-Safety Do Our Homes Have in Extreme Weather? https://rmi.org/resources/how-many-hours-of-safety-do-our-homes-have-in-extreme-weather/

Chicago

RMI. How Many Hours-of-Safety Do Our Homes Have in Extreme Weather? 2019. https://rmi.org/resources/how-many-hours-of-safety-do-our-homes-have-in-extreme-weather/.

Wikipedia

{{cite report |author=RMI |title=How Many Hours-of-Safety Do Our Homes Have in Extreme Weather? |date=24 July 2019 |url=https://rmi.org/resources/how-many-hours-of-safety-do-our-homes-have-in-extreme-weather/ |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{rmi2019how, author = {{RMI}}, title = {{How Many Hours-of-Safety Do Our Homes Have in Extreme Weather?}}, institution = {RMI}, year = {2019}, month = jul, url = {https://rmi.org/resources/how-many-hours-of-safety-do-our-homes-have-in-extreme-weather/}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }