Building Shell: How It Effects Energy Conservation

Building Shell: Snuggie For Your Home

Building shell & Conservation

Indoor air quality was not a problem at the turn of the last century, building shells were simply so drafty that the indoor air was always being replaced by fresh outdoor air. Firewood was cheap and grew everywhere so just throw another log on the fire, pull on a wool sweeter, and keep warm.

Today, the building shell is a little more important as we work much harder at saving energy and maintaining energy efficiency. The troubles the world has seen attempting to produce more and more energy has been well documented. Nuclear power plants near melt down, coal polluting the air, and Dams harming salmon runs.

Building Shell Function:

Today, the ideal building shell maximizes heat retention during winter and minimizes heat gains during summer to reduce the energy needed to maintain comfort. The best way to achieve energy efficiency in a new building is by energy-efficient design, energy planning, and quality construction methods. In existing buildings, technicians and contractors perform weatherization up-dates to reduce heat loss and gain through the building shell.

With the large metro areas we have today and the fact that every household has two or three cars, the building shell is not only being asked to separate hot and cold, but also indoor air quality and outdoor air pollution. There is not much use in installing an expensive electronic air cleaner if the outside air is permitted to blow through the building shell at will.

Making Weatherization Decisions Sometimes this is best left to a home energy auditor. With the need to reduce energy consumption, home auditors have been trained and are available both in the private sector and through businesses like your power provider. The auditor will take measurements and collect data that will assist you in making decisions concerning weatherization measures. Part of the audit will often include costs estimates and information showing return-on-investment. The important thing is to decide which retrofits provide the most energy savings that are in your budget.

Auditor Training:

Home energy auditors receive training from recognized training institutions in building construction, building shell heat flow, and building system diagnosis to ensure that the best conservation measures are chosen. Basic training takes several weeks and includes both classroom and hands on, in-the-field training. The auditor is trained to operate the various pieces of specialty instruments that are used during an audit. These instruments measure everything from building shell air leakage to the production of carbon monoxide associated with your combustion appliances.

Largest Home Energy Demand to Overcome Heat loss and gain through the building shell are the largest energy demands that residential homes need to overcome. To maintain comfort, the heating and cooling systems supply or remove heat at a rate roughly equal to the flow rate of heat through the building shell.

The amount of heating and cooling that a home requires throughout the year is directly related to the loss of heat through the floor, walls, and roof. To increase energy efficiency, the building shell must be weatherized and able to restrict the passage of air and heat.

Solar radiation, heat transmission, air leakage, and internal heat all challenge the quality of the building shell and in return determine just how may kilowatts and therms your going to be charged for on your utility bill.

Comfort and Cost The bottom line then comes down to two basic factors, comfort and cost. At what level of financial commitment are you willing to reach to be comfortable. Today, we expect our homes to provide a high level of comfort. For most of us, it is not OK to go around the house wearing a sweater and bunny slippers. Back in the days when a large home might have four or more fireplaces, it was reasonable to be uncomfortable in the back hallway, but not anymore.

The first thing we complain about is being uncomfortable and the second thing is how high the power bill has become. Both of these complaints are directly related to the quality of the building shell and the size of the power bill.

Building Shell Components:

Components of a quality building shell. I demolished a home that was constructed in 1909. The walls were two layers of rough cut 1 x 12’s with newspaper between. In this wall, both the boards and newspaper were air barriers – there was no insulation.


  • Paint is the first line of defense against the elements. Protects the exterior siding against moisture and solar destruction.

Exterior siding

  • Gives the wall shear strength and helps keep out raccoons and flies. Has some insulation value. Keeps the insulation that is in the wall cavity from falling out. Serves as an effective air barrier if supported by air sealing techniques at all corners, ends, edges and connections.

Rain Drain

  • Something fairly new as far as the building codes are concerned. This is a house wrap type application that maintains a space between exterior siding and wall sheathing. Suppose to allow moisture that gets behind the exterior siding drain out and dry without causing moisture damage inside the wall cavity. Little insulation value here.

House Wrap

  • As an extra barrier against the free passage of air through the wall assembly, house wrap has become a common building material. Please note that house wrap should be an air barrier and not a moisture barrier. Trapping moisture inside a wall cavity with a moisture barrier causes mold and dry rot.

Wall Studs and Framing

  • Supports the weight of the roof and provides something to attach both the exterior siding and interior wall covering to. Provides a thermal bridge that works against insulation values.


  • When installed properly, is the main product that restricts the transfer of heat through the wall. Most often installed in the cavities between the framing studs, between the floor joist, and over the ceiling, the insulation may well be the most cost effect building product in your home.

Interior Wall Sheathing

  • In most homes, drywall forms the interior wall surfaces. Cheap and able to take a variety of textures and paint, wall board becomes your homes best and most complete air barrier.

Interior Paint

  • Used mostly to protect the drywall and to provide a pleasant color to the wall. Homes that have been constructed since about 1985 have used a paint that is also rated as a moisture barrier. The idea is to keep humid moist air that is inside the home from getting into the wall cavities.

If any of the wall assembly pieces are faulty or installed incorrectly, the building shell is compromised and energy conservation is lost. When energy conservation is lost, the result is a noticeable and dramatic change in your power bill.

Your home has construction flaws that waste energy, reduce comfort, and encourage deterioration, and work against your energy conservation efforts. Knowledge about building shell characteristics will help you locate and correct those flaws.

Thank you for stopping by, please come back soon, but I won’t leave the light on for you…