Tag: Building Envelope

Baby It’s Cold Inside

Courtesy of the Urban Green Council

Typical buildings would be between 32°F and 43°F indoors. New buildings are a little better, but still not resilient. A high-performing building that has better windows, fewer air leaks, and more insulation would do much better. Without power, these buildings would stay at 54-66°F for a week or more.

Without electricity, buildings are dependent on whatever protection is provided by their walls, windows, and roof. In today’s buildings, that protection is modest at best. If it wore clothing, the typical New York City building would have a light jacket on—not what you’d wear outside in winter, and certainly not performance gear.

Only some buildings are constructed well enough to maintain their indoor temperatures without power. But to protect all New Yorkers, these resilient, high-performing buildings must become the new normal.

Computer models were created by Atelier Ten and based on six representative residential building categories to find indoor temperatures after a blackout within a single apartment. Summer and winter scenarios were defined by recent New York City weather data. The full report describes these models in detail.


  • Analysis
  • Conclusions
  • Read the Report

Within a building category, there are three important factors that influence temperature in buildings during blackouts. These are:

  1. The type and amount of window area,
  2. The amount of air that escapes through cracks and leaks in the walls, and
  3. The amount of insulation in the walls and roof.

All three factors can be improved during the design and construction of new buildings, and in the renovation of existing ones.

Glass conducts about five times more heat than a typical insulated wall. Therefore, between two buildings that are otherwise equivalent, the one with more window area will be colder during a winter blackout. Even the extra sun through a well-lit south window will barely make up for the absence of insulation; other windows will lower temperature faster than a wall would. During a summer power outage, glass causes the building to heat up more. Daylighting and energy benefits are minimal if windows take up more than 60 percent of wall area.

Using triple-paned windows can lower winter heat loss, although glass will never hold heat as well as insulated walls. In summer, any building can stay cooler with windows that are designed to allow in light but reflect heat, as do the windows in our high-performing models. Sunshades can also be added to windows to block the sun in summer but allow the low winter sun in.


Most residential buildings constructed more than five to 10 years ago leak substantial amounts of air heat through cracks and leaks in the walls, windows and doors. Plastic wrap is one common method used to stop this heat loss, which is why buildings under construction are wrapped in bright pink, yellow, or green film. Builders are reducing leakage even further with careful caulking and sealing. Eventually, drafts can be virtually eliminated, with all ventilation intentionally provided by systems that recover heat from the waste air being exhausted from the building. These improvements can also be made to existing buildings.

Adding insulation prevents heat loss through walls and roofs. New buildings can easily accommodate extra insulation, since it is straightforward to add it during construction. In most cases, insulation can be added to older buildings, either indoors or by adding a new exterior layer.

Over time, building codes have improved, meaning newer buildings have better windows, fewer drafts, and more insulation than they used to. But resiliency calls for high-performing buildings that go well beyond the current code. These buildings would use advanced practices and materials that are being deployed in the best buildings today. Described in detail in Urban Green Council’s “90 by 50” report, they incorporate windows that retain heat in winter and keep it out in summer, rigorous air sealing, and extensive insulation. Since these resiliency measures also save energy, they often pay for themselves, particularly in new construction.

Are You Spending Through The Roof?

Up to 16% of fuel in New York City buildings is used to heat air lost through rooftop vents according to a new Urban Green Council report

This wastes 80,000 barrels of oil and $11 million across the city every year.

Vents built into elevator shafts leak enough warm air throughout winter to fill the Empire State Building 29,000 times over.

In Spending Through the Roof, the New York affiliate of the U.S. Green Building Council (USGBC) looks at why so much air is lost through these vents, offer ways to estimate the impact, and provide clear advice on how to close or reduce their size to save energy—up to 16% of heating fuel is spent on leaked air—and money. See coverage in the New York Times to find out more.

Estimate your own savings with the Urban Green Council’s online calculator and learn more at their panel discussion on April 23rd.