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Building Envelope

Ways to Save Energy and Water

Building Envelope

Get Cash Back for Building Envelope Upgrades

Several programs offer cash incentives or grants for upgrading various parts of your building envelope. Ask a NYC Retrofit Accelerator Efficiency Advisor for details.

The building envelope refers to all barriers that separate the inside of a building from the outside, including the roof, walls, windows, doors, and foundation. Sealing air leaks, adding insulation, or replacing components of the building envelope will help keep warm air inside during the winter and cool air inside during the summer.

Air leakage through the building envelope can cause significant heat loss—often wasting up to 25 percent of the heat produced in multifamily buildings.

Air Sealing and Insulation

Many buildings lose heat as a result of air leakage through room air conditioning units that are left in place or uncovered during the winter. One of the biggest sources of heat loss is air leakage through open vents at the top of elevator shafts and stairwells on the roof. This lost heat can cost multifamily building owners an average estimated $3,400 each year, and taller buildings could spend well over $20,000 on wasted heat. To prevent heat loss, you can:

  • Cover open elevator shaft vents and stairwell vents with glass.
  • Install motorized louvers that stay closed unless an alarm system automatically opens them in the event of an emergency.
  • Remove or cover room air conditioning units during the winter.
  • Add or replace insulation in walls and on roofs.
  • Caulk or install weather stripping around windows to eliminate gaps around the frame.


Windows can account for 10–30 percent of heat loss in multifamily residential buildings. Replacing windows can significantly reduce these losses, although this may have longer paybacks than other efficiency measures. In addition to replacing windows, you can:

  • Seal gaps or cracks around the frame using caulk, weather stripping, flashing tape, and/or gaskets to reduce air leaks.
  • Add special coatings to existing windows to improve efficiency.


Roofs and Heat Absorption

Because heat rises, is often lost through a building’s roof in the winter. In the summer, sunlight can heat a flat, black asphalt rooftop to up to 190 degrees. A hot roof will heat the entire building, which causes your cooling system to work harder. To reduce energy waste, you can:

  • Insulate your roof to prevent heat loss in the winter.
  • Add a cool roof to reduce heat absorption in the summer by painting your roof with a highly reflective, light colored coating.
  • Install a green roof to reduce heat absorption by planting a layer of low maintenance plants on the roof.
  • Install a blue roof to reduce heat absorption and capture and retain rainfall in temporary ponds.

Building Envelope Resources

Roofs and Heat Absorption

Ready to Improve the Building Envelope?
Contact the NYC Retrofit Accelerator team today.