What is a Building’s Thermal Envelope?

A building’s thermal envelope won’t arrive in the mail, but, if done right, it can deliver energy efficiency.

What is it?

The National Renewable Energy Laboratory describes a thermal envelope is “everything about the house that serves to shield the living space from the outdoors.”

The thermal envelope includes the wall and roof assemblies, insulation, air/vapor retarders, windows, and weatherstripping and caulking.

It also is called the heat flow control layer. In simplest terms, what makes up the thermal envelope are the parts of a house (or building) that separate the heated/cooled area from the outside (or a non-heated/cooled area, such as a garage or attic).

Exterior walls, doors and windows can all be part of the building’s thermal energy. They each play a role in the overall air flow and energy balance of a building.

When you picture an older home, you may think of a drafty building that’s hot in the summer and freezing cold in the winter. Whereas a recently built home may be comfortable year-round. 

A house with a “tight” thermal envelope won’t lose much heating or cooling. A “loose” envelope results in a drafty home.

Insulation levels, energy-efficient windows, weatherstripping, caulking and a vapor retarder (which inhibits the movement of moisture) all play a roll in improving a building’s energy efficiency.

Even buildings with “tight” thermal envelopes must deal with “heat bridges.” A heat bridge (also called a “thermal bridge, “cold bridge” or “thermal bypass”) is an area where it’s easier for heat or cooling to move in or out. 

Heat bridges occur in locations such as where the door meets the wall, or where a wall meets a window. Any place with potential gaps could be a heat bridge.

Why does a thermal envelope matter?

Light blub laying on its side with the image of a green leaf inside

In the summertime, did your mother ever tell you, “Close the door, we’re not paying to air-condition the outdoors?” A building’s thermal envelope works along the same principle. 

Making your home or building as energy efficient as possible will save you money in utility costs. A home that can be heated (or air-conditioned) with a minimal amount of effort and retains that heating or cooling.

Whether you’re constructing a new building or updating an existing structure, there are always ways to improve a home’s thermal envelope.

International Energy Conservation Consultants can help to improve the energy efficiency of your home or office. If you are looking for a more accurate and thorough test, an energy audit can be done.  To learn more, contact IECC today. We look forward to hearing from you!

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