Earlier this year, the Building Performance Institute (BPI) introduced an entry level credential for Infiltration and Duct Leakage (IDL). According to BPI, this credential is going gangbusters. The reason: The 2012 and 2015 versions of the International Energy Conservation Code (IECC) have significantly stepped up requirements for limiting building air leakage and duct leakage. And while duct leakage testing was previously required under the 2009 code, gone now is the visual inspection option for verifying building air leakage. Blower door testing must be performed to verify air leakage limits. Training to achieve IDL Certification can teach you how to use a blower door and duct blower.
So far, only nine states have adopted the 2012 IECC (see "Status of State Energy Code Adoption"), although they include some big and influential states, including California, Massachusetts, Illinois, Minnesota, and North Carolina. Two more states - Florida and Nevada - have adopted the 2012 version, but it is not yet in effect. An additional two states - Vermont and Maryland - have already adopted the 2015 standard. It's probably not a matter of if, but rather of when, all U.S. builders will be required to meet the more stringent air sealing and duct sealing requirements.
Under the 2012 IECC, buildings in climate zone 3 to 8 must limit air leakage to 3 ACH50, down from 7 ACH50 (a big step!). For duct leakage, both the 2009 and 2012 IECC require duct tightness to be verified with either a post-construction test or a rough-in test, but the 2012 limits are much stricter. With the rough-in test, the 2012 IECC limits duct leakage to 4 cfm per 100 sq. ft. of conditioned floor area when the air handler is installed, and 3 cfm when it is not (down from 6 and 4, respectively). With a post-construction test, the 2012 IECC only contains a requirement for total leakage of less than or equal to 4 cfm per 100 sq. ft. of conditioned floor area (down from 12 cfm).
Meeting these stricter requirements needs deliberate effort. It's not a fall out of the boat and hit water kind of thing. Running around the job with a tube of caulk at the last minute ain’t going to do it. The cautionary tale from one BPI Building Analyst (see "Shades of Gray in Residential Construction Morality," Home Energy Pros, April 27, 2015) tells of one contractor’s efforts to meet the new testing limits that are kind of funny. But the consequences (read the comments) are enough to make you cry.
For guidance on making a deliberate effort at air sealing the envelope, see the U.S. Dept. of Energy's Better Technologies Program Air Leakage Guide (PDF).