What is a building envelope?

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The building envelope represents the volume of space that you want to heat or cool, explains Michael Trolle of BPC Green Builders in Wilton, CT. “Unless you define and treat the entire perimeter of this space, you will lose (waste) energy meant to heat or cool the space at an accelerated rate. Treating the perimeter means to make the foundation, framed walls and roof airtight, insulated to a high level, with some of that insulation continuous across the framing. The better the job you do on this, the more you will slow down the flows of energy,” says Mike. “A house with very slow energy flows through the envelope is by definition energy efficient. An energy efficient home saves you money and is much more comfortable.” This BPC Green Builders home combines both traditional and contemporary design elements.

The front wall of the house features a unique and elegant curve echoed by the 2nd floor balcony that runs across the full face of the house, providing shelter to the main entry below. Like all BPC homes, this one exceeds the Energy Star for Homes certification standard and is also expected to be certified within the LEED for Homes program, following the completion of landscape elements. The exterior features fiber cement shingles above and fiber cement panels below. The trim is an engineered wood product, and the windows feature triple glazing and exceed Energy Star standards.

Building materials play an essential role in determining a home’s ability to store heat. Today’s construction pays extra attention to a factor called thermal mass—those materials’ ability to absorb and store warmth and coolness until needed. The idea is to make choices that limit fluctuation in indoor temperature and, in turn, reduce your heating and cooling requirements. Thermal mass building materials can be traditional or extremely high-tech.

Here are the key components of the building envelope that impact indoor temperature control:

  • The right insulation prevents the unwanted flow of heat from a warmer to a cooler space so you don’t end up with cold or hot pockets and high heating and air-conditioning bills. Insulation has gone high-tech with spray foams as well as rigid foam, natural fiber options, concrete block and forms and barrier sheets, among others.
  • The right roofing materials can help you better manage energy as well. In hot climates, high-performance materials can reflect heat rather than absorb it, cutting your need for air-conditioning. With solar panels on the roof, you can capture and re-direct that heat.
  • Walls, windows and doors are also part of the building envelope. As with the roof, the amount of energy lost or retained through walls is influenced by design and materials, making wall insulation key. The placement of windows and doors can help reduce energy loss and, for windows and skylights in particular, determine the extent of your lighting needs—in the right locations, they’ll bring in more natural light and warmth. New window materials and coatings mean higher-performance—you may be able to cut energy consumption at least 10 percent and possibly as high as 50 percent depending on where you live.