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 IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. 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 barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. 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 ACHACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations. 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:

• Wall insulation must be “installed in substantial contact and continuous alignment with the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. air barrier.”
• Wall corners must be insulated. (This is rather vague — do two-stud corners without any exterior foam meet the intent of the code?)
• The “space between window/door jambs and framing” must be “sealed,” and “air permeable insulation” cannot be “used as a sealing material.”
• Rim joists, window headers, and door headers must be insulated.
• Insulated floors (for example, cantilevered floors or insulated floors over garages) must have insulation “installed to maintain permanent contact with the underside of the subfloor.”
• There is a requirement for crawl space walls that “Insulation is permanently attached to walls.” (This requirement is unclear; it’s hard to tell whether uninsulated crawl space walls — for example, in a ventilated crawl space with insulation between the floor joists — are permitted.)
• “Showers and tubs on exterior walls” must “have insulation and an air barrier separating them from the exterior wall.”
• There is a requirement for “electrical/phone box on exterior wall” requiring that the “air barrier extends behind boxes or air sealed type boxes are installed.”
• “HVAC register boots that penetrate the building envelope” must be “sealed to subfloor or drywall.”

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 PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. 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 testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas.. 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 N1102.4.2.1] 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.”