Defining habitable temperatures

Tuesday June 18, 2013

Over the past five months, the New York City Buildings Resiliency Task Force has been working to figure out how to make buildings in the city more resilient. The Task Force, which was created at the request of Mayor Michael Bloomberg and City Council Speaker Christine Quinn in the wake of Superstorm Sandy and facilitated by Urban Green, the U.S. Green Building Council Chapter in New York City, issued its recommendations on June 13, 2013.

The Task Force included about 200 people organized into four building-type committees (commercial buildings, multi-family residential buildings, critical buildings, and one-, two- and three-family homes and three Working Groups (Structure, Façade, and Interiors; Electrical and IT; along with HVACR, Plumbing and Fire Protection). I participated in several meetings as an at-large member of the Task Force.

The findings were presented in a 40-page Summary Report as well as a much longer, 185-page document that includes detail on each of the 33 proposals being presented to the city. It is important to note that these are advisory recommendations only; there is no guarantee that any will be acted on.

The report includes five types of recommendations based on suggested implementation: Required Actions, which would be mandated as retrofits for existing buildings (there are very few of these); New Code measures that would be incorporated into codes for new buildings and major remodeling projects; measures that would Remove Barriers to creating more resilient buildings; Recommended Practices; and measures that require Further Action.

These 33 proposals range from providing access to potable water in multifamily residential buildings at a level in the buildings where municipal pressure will deliver the water (so that residents on upper floors will have access if pumps in the building are inoperable), preventing sewage backflow into basements (a huge problem with Sandy), ensuring operability of toilets and sinks during power failures; eliminating existing barriers to elevating buildings above flood levels, capturing stormwater to reduce flooding, providing quick connections to temporary (mobile) generators and boilers, and requiring operable windows.

Maintaining habitable

interior conditions in

the event of lost power

The measure that I’m most excited about in the Task Force report is a proposal to Maintain Habitable Temperatures Without Power. This has been a key tenant of the "resilient design" agenda I’ve been advancing through the Resilient Design Institute (RDI) and the concept of "passive survivability" that I’ve been pushing for since late 2005, following Hurricane Katrina in the Gulf Coast.

When power was lost in parts of New York City -- in some places for several weeks -- there was recognition by the city that conditions could get pretty dire very quickly, especially in high-rise residential buildings during hot weather (projected to become a more common occurrence). In the summer, temperatures may rise quickly to dangerous levels, and in the winter, temperatures will fall. We can refer to these as "drift temperatures."

This is a big issue in New York City, which houses a remarkable 11 percent of the nation’s occupants of high-rise apartment buildings. There is clear recognition that evacuating millions of residents due to a weather event -- or something else -- that knocks out power for an extended period of time. With a population of 8.3 million, there simply isn’t a way to carry out a widespread evacuation; there has to be a way for residents to "shelter in place."

What defines
habitable temperatures

This brings me to one of the early focus areas of RDI: Defining what constitutes "habitable" or "livable" conditions. In May of this year, RDI sponsored an all-day retreat of leading energy engineers, architects, planners, and public health experts to brainstorm metrics of resilience, including temperature and humidity. In follow-up to this "Benchmarking Resilience" retreat, a meeting participant and colleague, Seth Holmes, AIA, of the University of Hartford, will be taking the lead with a more in-depth literature review and expert interviews. We are hoping to produce a peer-reviewed technical paper on these issues in the fall.

There are a lot of factors that come into play with the question of habitable conditions, including humidity (with higher humidity, moisture doesn’t evaporate as easily from our skin and we suffer more from the heat), duration (putting up with no air conditioning for one day is one thing, putting up with it for a week or two is very different), and perhaps regional adaptation.

Before the availability of air-conditioning, it was a pretty reasonable assumption that people in the south could deal with heat better than us northerners, but that may not be the case as much today. In fact, some suggest that those of us up north may now be better adapted to hot, humid weather than our southern neighbors, because we aren’t always in air conditioned spaces. My guess is that we’ll end up with something like 90 degrees Fahrenheit, with some correction for relative humidity as a reasonable upper boundary for habitability.

At the low-end of the livable temperature range, perhaps the argument for regional adaptation is stronger. My sense is that 50 to 55 degrees Fahrenheit is a reasonable lower boundary for livable conditions -- perhaps 50 degrees for more northern climates and 55 degrees for southern locations, where the blood is thinner.

Buildings that maintain
habitable conditions

Once we determine what a reasonable temperature range is for habitability -- not comfort, mind you, but survivability -- we can figure out what building design measures are needed to achieve those drift temperatures. And we should be able to model that performance using energy modeling software.

Really well-insulated buildings will maintain the habitable conditions much longer than conventional buildings -- perhaps even indefinitely. A home built to Passive House standards (a rating system for ultra-low-energy buildings that emerged in Germany and is gaining popularity here) incorporates not only very high insulation levels, super-high-performance windows, and very low air leakage, but also some passive solar gain.

In most places, such a home will never drop below 55 degrees Fahrenheit or perhaps even 60 degrees in winter with no supplemental heat. And in the summer if such a house is wisely operated (closing windows during the day, for example), it should maintain temperatures significantly cooler than outdoors.

Moving ahead with this work

The Buildings Resiliency Task Force in New York City listed the proposal on maintaining habitable temperatures during power outages as a measure needing further action. Urban Green is hoping that the work of the Task Force can be continued into the fall to provide more detailed guidance on this and a number of other proposals.

If that extension is approved, I’m hoping that RDI will be able to provide detailed guidance, both on the metrics and on achieving such performance in buildings. We are still seeking foundation grants to support this work -- so let me know if you have suggestions of foundations, corporations, or agencies that might want to support this work.

Alex Wilson is the founder of BuildingGreen, Inc. and the Resilient Design Institute (, both based in Brattleboro. Send comments or suggestions for future columns to


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