Residential duct leakage testing under the 2009 IECC
Does the 2009 IECC require residential duct leakage testing when ducts run within exterior walls?
The answer is not black and white. An exception applies to the required duct leakage test at section 403.2.2 if all ducts are “located within conditioned space.” Conditioned space is defined as “…containing uninsulated ducts….” So what happens when ducts run within exterior walls up to a second floor register? By definition they seem to be within the conditioned space, being uninsulated from the interior space because of their separation by only drywall and likely the polyethylene vapor retarder / air barrier. However, the exterior wall duct is outside the air barrier, so from a building science perspective it would clearly be outside the conditioned space.
Given the attention 2009 IECC pays to the air barrier, it is unfortunate that the “conditioned space” definition does not include a reference to the term. Then there would be no question that ducts running within exterior walls would be outside the conditioned space. And a duct leakage test would be required for those houses.
The consensus I’ve heard is that yes, 2009 IECC should be interpreted as ducts running within exterior walls should be considered outside the conditioned space. Thus for the 90 percent compliance surveys in Minnesota, we are planning to do duct leakage testing for houses with ducts running within exterior walls.