Dan Bossenbroek

Your Personal Home Energy Audit Looking at the Building Envelope



Posted: Friday, September 04, 2009

by Dan Bossenbroek
Just Green Homes

The main purpose of an energy audit is to help determine which strategies to use in order to save the most energy for the smallest investment. Today, it's time to turn your attention to the building envelope, otherwise known as the stuff that separates the inside from the outside: walls, ceilings, roofs, floors, doors and windows. This is the one area where you use more energy than any other, 43% on average. Before you start measuring, you should print out the photographs of the outside of your house that you took when you put together your site plan and a copy of your site plan. This will help you keep track of the sizes of walls, doors, windows and other elements.

The first step is to take a peek up into you attic. Most houses are insulated similarly throughout an entire system like the attic, but you will need to verify this. While you are up there, you will also want to note what type of insulation there is, and measure its thickness. The most common types of attic insulation are fiberglass batt, usually pink; blown fiberglass, small bits; and blown cellulose, chemically treated recycled newspaper. However, spray foam insulation and radiant insulation are gaining popularity. You will also want to notice if there are areas where there is a continuous layer of insulation, an area which is not broken up by wood ceiling joists (cavity insulation). Next you need to calculate the area of each different insulation condition. These areas will probably align with major areas of your house, for instance the attic of the one story addition may have different insulation than that of the two story original house. Refer to your site plan for dimensions. You should also start a chart with these headings: Building Element, Cavity Insulation, Thickness, Continuous Insulation, Thickness, and Area. Under Building Element you will list Ceiling/Attic Type 1, Ceiling/Attic Type 2 and so on. Before you move on to the next step, you must first subtract the area of any skylights from the ceiling/attic areas.

After you have filled in the attic information in your chart, it is time to examine your floors. Are there any floor areas in your house that are above unheated spaces? You may have an addition over an unheated crawl space, a bedroom over a porch, or a bonus room over a garage. Add these spaces, Floor Type 1, Floor Type 2, to your chart and fill in the types of insulation and their thicknesses. For those areas that are above unheated, but enclosed spaces such as garages and crawl spaces, add 50% to the thickness of the insulation. These spaces act a buffer to the outside.

The next Building Element type to examine is slab on grade floors. A slab on grade is a concrete floor that is built directly on the ground. There are several ways that the edge of a slab on grade can be insulated, and most of them are difficult if not impossible to verify without demolishing part of the floor, but are equally effective, so assume that there is 2" of rigid insulation. Here, the area of the floor is not important, but the perimeter is. Enter the perimeter of the slab on grade in your chart feet (ft.) instead of in square feet (s.f.).

Basement and conditioned (heated and cooled) crawlspace walls are the next item to measure. Here, you will want to separate the areas into those above grade, or above ground, and those below. You may want to mark the basement dimensions on the photographs of the outside of your house. This will be especially helpful if the grade slopes along the sides of your house. Fill in your chart and add 50% to the insulation thickness for the basement areas that are below grade, and for those walls that adjoin unheated crawlspaces. In addition, subtract the area of the windows.

Now you can now turn your attention to the exterior walls of your house. Measure the floor to ceiling distances and add the second floor height and another foot for the floor structure to the height of the first floor. Calculate the areas for the different types of walls, subtract the area for all doors and windows, and add this information to your chart. Here too, you may want to write the areas of widows and doors on your photographs. In order to determine the type of cavity insulation in wood framed walls, your best bet will be to remove the cover plate from an outlet or switch. You may need to remove several before you see evidence of insulation around the edge or poking through a hole in the back of the box. Determining the type and thickness of continuous insulation on the outside of walls is more difficult. The most likely place to find this out is at one of the gaps around a pipe, vent or wire that pokes through the outside of your house, this may require you to remove some caulk. If you have un-insulated masonry walls, enter the thickness of the masonry in the continuous insulation column, if they are insulated, enter the thickness of the insulation. Again, remember to subtract the area of all doors and windows before you enter the various wall areas into your chart.

You have now examined the building envelope of your house and thus completed the third step in the process of collecting information for your home energy audit. Click here to request a Home Energy Audit Excel file to enter your information in. The next article will help you examine your windows, doors and other areas that you may need to weatherize.

Dan Bossenbroek is a registered architect and has been incorporating energy conservation design strategies into his projects for over seventeen years. He has extensive experience in residential design, is a Leadership in Energy and Environmental Design Accredited Professional (LEED AP) and his area of expertise is high performance buildings and sustainable design. Furthermore, he is an avid do-it-yourselfer having renovated several older homes. For energy saving products and home improvement advice he recommends www.justgreenhomes.net

Dan Bossenbroek is a registered architect and has been incorporating energy conservation design strategies into his projects for over seventeen years. He has extensive experience in residential design, is a Leadership in Energy and Environmental Design Accredited Professional (LEED™ AP) and his area of expertise is high performance buildings and sustainable design.  Furthermore, he is an avid do-it-yourselfer having renovated several older homes.  For energy saving products and home improvement advice he recommends www.justgreenhomes.net
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