Say hello to the 2012 Virginina Energy Conservation Code. And with it, stricter air leakage requirements with a decrease in allowable air exchange rates.

Air exchange rate is the rate at which air flows into and out of a given space through penetrations and openings from areas outside the conditioned space including the environment, attics, garages, basements and crawlspaces. One full air exchange is when a volume of air equal to the volume present within the home at any given time is renewed with outside air. Air exchange is good when the air path is intentional and predictable, but when chaotic and unintentional it may cause sickness, odors, moisture issues, increased energy use and over time, structural damage.

The current construction code requires a contractor to chose between a visual inspection of the building envelope or diagnostic testing. Both options require compliance with numerous air sealing measures throughout the home and must occur after all penetrations in the building envelope have been created. However, the visual inspections must occur while the sealing measures are still visible, generally prior to commencement of drywall procedures. If timing and/or scheduling become an issue on the job site, diagnotic testing with a blower door system is the only viable option to prove code compliance.

During the blower door test the given space is depressurized with a large fan by which the locations of air leaks are detected and a quantifiable air leakage value is determined.  This air leakage value, or rate, is then compared to the code requirements to ensure compliance. This is a great advantage over the visual inspection option because the contractor can then remediate applicable leaks immediately and confirm the benefits and added value of the construction methods used.

In order to comply with the current 2012 code, a maximum air exchange rate for single family homes and multi-family buildings up to three stories in height have a threshold of (5) air exchanges per minute when under a designated pressure as tested by a blower door. This is a decrease of (2) air exchanges from the 2009 code requirements.

What does this mean to you, the contractor and home owner or buyer?

So glad you asked!

Let’s look at an example for a simple 2,000 square foot home with standard 8′-0″ ceilings.

Per the current 2012 code, which allows (5) air exchanges per minute under testing conditions, an equivalent cumulative hole to outside unconditioned air equal to 12″ x 12″ (1333 cfm) is the air filtration limit. This is a noticeable derease from the 2009 code which allows (7) air exchanges per minute under testing conditions and a cumulative hole equal to 14″ x 14″ (1867 cfm).

This may not seem to be a significant difference, but think of it this way. . . would you rather that your bedroom window be opened 6.0″ or 4.5″ on a blazing summer afternoon or a snowy winter night? We know our answer! How about you?

With this code change, there will be other important things to consider. If less air is infiltrating from unwanted and unknown places, how will we pull fresh air into our homes and draw out the polluted air? Answer: Please welcome the properly designed and installed HVAC and/or mechanical exhaust system onto the scene. . .

Join us again soon as we discuss typical components of these proper ventilation systems.


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