One of the most cost-effective ways of lowering residential energy costs is to reduce a home’s air leakage rate, so it makes sense for energy codes to ratchet up air-sealing requirements. The latest (2009) version of the International Residential Code does exactly that.
Just like the earlier 2006 code, the 2009 IRC includes a requirement (in section N1102.4.1) that “the building thermal envelope shall be durably sealed to limit infiltration.” The language in that section is unchanged; the code still requires that “The following shall be caulked, gasketed, weatherstripped, or otherwise sealed with an air barrier material, suitable film, or solid material:
1. All joints, seams and penetrations.
2. Site-built windows, doors and skylights.
3. Openings between window and door assemblies and their respective jambs and framing.
4. Utility penetrations.
5. Dropped ceilings or chases adjacent to the thermal envelope.
6. Knee walls.
7. Walls and ceilings separating the garage from conditioned spaces.
8. Behind tubs and showers on exterior walls.
9. Common walls between dwelling units.
10. Other sources of infiltration.”
New air sealing requirements, with two compliance options
In addition to these provisions, the 2009 IRC includes further air-sealing requirements in section N1102.4.2.
This new section gives builders two options: either the builder must comply with the requirements of an air barrier and insulation inspection checklist (Table N1102.4.2), and submit to a “visual inspection,” or the builder must show that “tested air leakage is less than 7 ACH when tested with a blower door at a pressure of 50 pascals.”
The checklist option
The items on the air barrier and insulation inspection checklist (see Image 2, below) make sense, although two provisions (the provisions requiring that crawl space walls and the corners of above-grade walls must be insulated) are vaguely worded and therefore ambiguous.
Here’s a partial list of the checklist items:
The code states that the items on this list should — “where required by the code official” — be “field verified” by “an approved party independent from the installer of the insulation.” The language leaves some wiggle room, implying that the code official has the discretion to allow a builder to self-certify that these items are complete, or even to waive the checklist requirements altogether.
The blower-door option
If a builder chooses the blower-door option, the bar has been set quite low. While Passivhaus builders are aiming for 0.6 ach50, and many energy-efficient builders strive for 1.5 ach50, the building code is satisfied if your home is quite leaky: All you need to show is 7 ach50.
The code is fairly specific about the circumstances of the blower door test. It requires that “testing shall occur after rough-in and after installation of penetrations of the building envelope, including penetrations for utilities, plumbing, electrical, ventilation and combustion appliances.” It also specifies which openings should be open during testing (interior doors), which openings should be closed but not sealed (windows, exterior doors, fireplace doors, dampers), and which openings should be sealed (exterior openings for ventilation systems).
However, the writers of the code provision forgot an important detail: the code is silent about who is allowed to perform the test. As written, the code allows anyone to perform a blower-door test. In fact, builders can conduct their own blower-door tests — in effect, they can self-certify the air leakage rate of the home they are building.
Even though it’s not written there, my interpretation says that it is
In light of this obvious mistake, building code experts are scrambling to present their own interpretations of the new code. One source notes (correctly) that “verification requirements are up to the AHJ” — that is, the “authority having jurisdiction,” otherwise known as your local building official. Of course, that’s true — local code officials have always had broad authority to interpret the code as they see fit.
Similarly, Lynn Underwood, an advisor at GBA, interprets the new code this way: “the locality has the right to accept (or not accept) the individual performing the [blower door] test and evaluation.” According to Michael DeWein, the technical director at the Building Codes Assistance Project, “Most are interpreting it [section N1188.8.131.52] to mean that someone who is qualified must perform the inspection, i.e. a rater, BPI-certified analyst, or shell specialist.”
However, it’s quite possible that some builders will resist the idea of complying with a code “requirement” that doesn’t appear in the code. I see no reason why a builder couldn’t rebut a code official’s insistence that a blower-door test must be performed by a third-party inspector with this simple challenge: “Show me where it says that I can’t do the test myself.”
According to DeWein, at least one state — New York — caught the code error before incorporating sections of the 2009 IRC into the New York building code and included a provision requiring a qualified third-party technician to perform the referenced blower-door test.
Last week’s blog: “Calculating the Global Warming Impact of Insulation.”