Building Shell 101: Heating bills through the roof!

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Any true Minnesotan will tell you that making it through our harsh winters is all about having a warm home that will keep you comfortable even if it gets down to 30 degrees below zero. Your home does this by physically separating your living space from the weather outdoors. The walls, windows, doors, floor, and ceiling that form this protective barrier between you and the cold is called the building shell.

Heating the space inside the building shell will keep us warm, but it comes at the price of the fuel we have to burn to maintain a comfortable temperature. So the better the building shell is at maintaining that barrier between you and outside, the less fuel you will need to burn to keep your home warm, and, more importantly, the more money you will have to spend elsewhere.

Without getting too technical, a brief physics lesson can help to shed some light on how your home loses heat. Firstly, heat is a type of energy and energy likes to move from areas of high energy to areas of low energy. In your home this means the heat in your house is going to want to go from where it is warm to where it is cold. Secondly, warm air is less dense than cold air. This means that warm air rises over cold air (think hot air balloon). So if your home is warm and it is cold outside, that heat energy from your home is going to try to get out any way it can, particularly through the roof.

Heat mostly escapes from the home through one of two ways:

  1. Air Leakage: Warm air escaping through gaps or cracks in the building shell i.e. gaps in the attic, cracks in the walls, etc. This accounts for about 35% of heat loss in an average home.
  2. Transmission: Heat transmitted through the materials of the building shell i.e. through walls, ceiling, floor, etc to the air outside. This accounts for about 40% of heat loss in an average home.
Home envelope

With this in mind, it is easy to see how even modest improvements to the building shell can dramatically reduce your monthly energy bill.

Though no home is or should be completely airtight, filling the gaps that air is leaking through is one of the smartest things you can do to reduce your energy bill. Since warm air rises, typically the most important leaks to fix are those in the attic. This can be done by caulking cracks and gaps. Reducing air leakage can also make your home less drafty and more comfortable, and of course, save you a ton of money.

Preventing heat loss through the materials of the building shell can be as simple as adding more material to the shell in the form of insulation. Insulation serves to slow the transmission of heat through the walls of your building shell. Think of hot coffee in an insulated mug opposed to a paper cup: which one will stay warm longer? Having an additional layer of insulating material around the mug naturally slows the heat loss of the coffee much more than the walls of a paper cup. Insulation comes in many forms and can be installed in the walls, floors, and ceiling of your home. Again, since warm air rises, insulation in the attic typically stands to save you the most money.

Air sealing to limit air leakage and insulation to limit heat loss through transmission are two of the best measures you can do to improve the energy efficiency of your home. As if these savings weren’t enough, these home improvements are relatively inexpensive and the savings on your energy bill typically repay your initial investment within a few years.