During a professional roof inspection, Bergen County roofing experts may perform a series of calculations to determine how much air infiltration a house is experiencing. This information is important not only in determining why a home is using more energy for heating and cooling than it should, but also for the homeowner's level of indoor comfort. Air infiltration also has significant impacts on a roof's longevity and performance.
Most homeowners who have infiltration calculated as part of a home energy audit do so on houses built before the 1970s, as homes built since then are usually sealed tightly. The audit may be done as a result of unexpectedly high summer air conditioning expenses or wintertime heating costs. A homeowner could also have the air infiltration numbers examined if they are trying to reduce their carbon footprint or put the home up for sale.
To calculate the amount of air infiltrating the house, roofers begin by doing a blower door test. This measures the amount of air needed to pressurize a building to a specific level compared to the outdoors. It is measured in cubic feet per minute. The pressure used for this test is 50 Pascals, which is a unit of measure for air pressure.
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Next, the roofers calculate the home's volume in cubic feet. If the house is a simple shape, it can be done with the exterior measurements, including length, width and height. Then the pressure reading from the first step is divided by the building's volume. After determining this number, the roofers then multiply the result by 60 to arrive at the number of air changes per hour, which is referred to as the ACH50. This is the number of times per hour the air within the house is totally replaced by outdoor air.
Next, the roofers will consult the U.S. Department of Energy's tables for building LBL factors, an acronym for the Lawrence Berkeley Laboratory that created the procedure for estimating air leakage. A building's LBL depends on its climate zone, height and shielding from the wind. The ACH50 is divided by the home's LBL to get the number of natural air changes per hour. This final number is the unwanted air infiltration.
If the air infiltration level of a home is high, roofers can take several steps to fix the problem. Air sealing and adding insulation are the top two actions that can be performed by experienced roofing professionals. Other important steps include caulking around door and window frames and sealing up small cracks in the home's foundation.