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Thu, Aug. 22

GREEN BUILDING: Seal common leakage locations to save energy, money

Question: I had an energy audit and found my air leakage is higher than expected. What is my next move?

Answer: Most energy audits determine the overall level of leakage for your homes living space and, while useful, it doesn't tell you where the problems exist. Once you have these results, you can decide what improvement level you want to target and how much you wish to spend. The tighter the home the better, but there is a limit to what can be done for existing homes that weren't built with high energy-saving standards in mind.

An ideal leakage target for a new home would be the 2012 International Energy Conservation Code that stipulates that in climate zone 4 (Prescott) that the maximum leakage be limited to three living space air changes per hour (ACH). ACH is based on the air volume of your home's conditioned living space. As an example, a 2,000-square-foot living space home with 8-foot ceilings has a volume of 16,000 cubic feet (cu ft). 3ACH50 equates to changing 3x16000 cu ft of air per hour using a blower door tester, set to an indoor/outdoor 50 Pascal pressure difference. The tightest homes can reach 0.6ACH50, and my LEED gold home registered 1.6ACH50. As with many building science calculations, ACH is scalable to conditioned space.

For existing homes, a rule of thumb is to establish the current ACH50 using the blower door measurements and look for a 20 to 30 percent improvement. As an example, a typical home that registered 2,500 cubic feet per minute (cfm) leakage and has a living space of 16,000 cu ft would have an ACH50 of 9.3. A 30 percent drop would achieve an ACH50 of 6.5 and a reduction of 45000 cu ft of air being heated or cooled each hour.

For this simple example, the cash savings would be approximately 29 cents an hour for natural gas heating and 88 cents an hour for electric heating; over a year, this can really add up. You have also reduced the number of uncomfortable drafts and potentially cold and damp rooms in your home.

A recommendation would be to attack the problem in stages and hire a contractor who understands energy focused building science and blower door diagnosis. Using a blower door tester, a wet hand, a smoke generator or infrared camera, find leaks around doors and windows, electrical sockets and where pipes leave and enter different conditioned and unconditioned spaces; these are the easiest to fix and can have a significant effect.

Other common leakage locations are between the basement or crawlspace walls and the main floor and wall perimeter framing; also slab perimeter framing. Another area that's prone to leaks is an unconditioned attic, again at the perimeter wall and roof joist framing, trap doors, chimneys, wiring and piping conduit and any recessed lighting fixtures. All these connections should be air-sealed with caulk or closed cell foam insulation.

At this stage you could use the blower door to re-measure and obtain progress numbers. One more option would be to install an air and vapor barrier on the outside walls if one does not exist, but this would require removing the outer wall cladding and involve higher cost. The heating and cooling system can also have a major pressurizing effect on leakage, but is beyond the scope of this article and will be discussed later.

For more information, visit www.greenhomeenergy advisors.com and www.greenhomeenergyaz.com.

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