Building Envelope

What is the Building Envelope, and Why is it is so Important to Energy Efficiency?

Simply stated, the building envelope is the physical barrier between the conditioned environment (heated or cooled) and the unconditioned environment. The envelope typically consists of walls and insulation, doors, windows, and roofs. These components work together to keep conditioned spaces comfortable for residents by minimizing the amount of heat transfer between the interior and exterior.

The building envelope is the most important aspect of a building’s design when considering energy efficiency—envelopes that leak air excessively or conduct heat can easily cause energy-intensive equipment, such as heating and air conditioning units, to work more often and strenuously. The result is higher energy bills and less comfortable living spaces.

Why Upgrading the Envelope During a Retrofit is Crucial

Since upgrading the efficiency of the envelope is most feasible during construction or a deep retrofit, the Multifamily Upgrade Program (MUP) strongly recommends improving the envelope as much as possible during a planned upgrade. Addressing the envelope will considerably reduce energy loads, translating to lower utility bills. Due to the tighter envelope, smaller energy loads require smaller sized equipment and systems such as boilers or heat pumps.

Design Strategies: Passive Versus Active

When performing retrofits, properties should leverage active and passive design strategies. Active design strategies use mechanical energy to condition buildings. Passive design strategies use ambient (free) energy, e.g. heat from the sun, natural ventilation, and daylighting. Most multifamily buildings use a hybrid approach to incorporate both active and passive design to provide comfort. Property owners and energy consultants should analyze building orientations and envelopes to assess which passive strategies they can employ while meeting the remaining conditioning needs with mechanical systems.

As stated, there are few opportunities to actively improve the building envelope’s efficacy—typically only during construction or during a retrofit. Properties should take advantage of a retrofit to drive down energy loads, reduce the size of needed mechanical equipment, and optimize passive and active strategies.

MUP-Incentivized Building Envelope Improvements

MUP incentivizes the installation of building materials and equipment that provide energy efficiency above California building code. For the building envelope, this includes:

  • High-performance windows such as double/triple pane with low emissivity coatings and vinyl frames
  • Attic insulation
  • Wall insulation
  • Cool roofs with higher solar reflectance

Other Improvements

If upgrading the envelope is not viable, there are many low-cost upgrades and strategies you can use at your property to reduce leakage and improve the efficiency of your property that do not require significant construction work.

These auxiliary improvements are outlined below; these cannot be modeled directly in energy software and, so are not incentivized through MUP. You can implement these upgrades independently or with the major envelope improvements discussed above.

Fix air leaks

Common air sealing techniques include caulking and weather-stripping around doors, windows, plumbing fixtures, and ceiling fixtures, and installing foam gaskets behind electric outlets and switch plates. Note, the US Department of Energy estimates that caulking and weather stripping air leaks provides a simple payback of one year or less. To learn more about building air sealing, click here.

Use window attachments

During periods of cold weather, about 30 percent of a home’s heating energy is lost through windows. In contrast, in hot climates approximately 76 percent of sunlight that hits a standard double-pane window enters the home and becomes heat, forcing more use of cooling equipment like air conditioners and ceiling fans. There are many types of window treatments like shades, blinds, and films that give building occupants more control over daylight entering the occupied space and minimize heat gain (or loss), which will reduce energy use. To learn more about energy efficient window treatments, click here.

Provide resident education

While residents often pay their own utility bills, many multifamily properties offer perks such as use of common areas and paid water bills. When properties pay for energy and residents control use, achieving energy savings can be difficult. However, promoting energy conservation by appealing to social norms can help your property lower utility bills. To learn more about resident education, click here.