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House Envelope

Everyone likes a warm coat outside in the winter, so does your house!

One of the most important things that makes a home energy efficient is the envelope of the house.
The envelope of a home is comprised of the walls, windows, roof and foundation.

The goal is to have as little transfer of the warm air from inside escape to cooler air outside (or the reverse in the summer).
This can happen through air movement, due to drafty windows for example, or through thermal transmission of heat, also called thermal bridging.

For the first, you want to eliminate or minimize holes and unnecessary joints. Every angle is a weak spot, so minimizing those makes the home better insulated. A good vapor/moisture barrier and careful wrapping around windows and doors is also very important.

Thermal bridging happens as thermal energy wants to equalize, warm air will travel from warm to cool.
You can see how thermal transmission works by cooking something in a pan. When you turn on your stovetop, you aren't heating the food directly. You are heating the pan, which then heats the food.
In a house, you don't want that thermal energy to escape. If the walls were made of metal, in the winter, it would be very easy for the warm air inside to warm the metal, which then would try to warm the cooler air outside.

Wood doesn't transmit heat as easily as metal, but it still will.
For this reason, a house with studs every foot will transmit more heat to the outside that a house with studs every two feet.

In our house, we built the walls out of a 2x4 stud wall, then a gap, then another 2x4 stud wall.
This way the wood is not continuous through the entire wall, minimizing thermal bridging.
Another advantage to this is it gives us lots of space for insulation and costs less than some other advanced framing techniques.

If you are interested in a more detailed, technical description of thermal bridging, Wikipedia.org has a great description.
©Copyright 2017 Mark Hanson
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