Airtight Approach to Achieving Building Performance

by Marcy Marro | September 1, 2022 12:00 am

This is why many jurisdictions are adopting airtightness requirements from the International Energy Conservation Code (IECC) and ASHRAE 90.1, including Utah, Washington, New York City, Seattle and Fort Collins, Colo. At the federal level, the U.S. General Services Administration (GSA) and the United States Army Corp of Engineers have also established infiltration standards for their buildings. Airtightness requirements are also critical to voluntary standards such as Passive House Institute U.S. (Phius) certification, and to zero net energy goals. Whether focused on minimum code compliance or progressive energy and carbon goals, project teams need to pay attention to building enclosure airtightness to meet building performance expectations.

How are airtightness requirements specified?

Performance requirements are specified as a maximum cubic feet per minute (CFM) of air infiltration divided by the total conditioned enclosure area of the building (cfm/ft2). The enclosure is defined as anything that separates the interior space of the building from the exterior. For example, the Washington State Energy Code sets a threshold of 0.25 cfm/ft2 while Phius certification targets infiltration below 0.08 cfm/ft2, a significantly more stringent standard.

How is performance measured?

Airtightness is determined after construction completion by conducting a whole-building air barrier test, sometimes referred to as blower door testing. Trained technicians with calibrated test equipment quantitatively measure the total cubic feet per minute of airflow through the building enclosure at a specified test pressure by placing fan assemblies in exterior doorways to pressurize/depressurize the building. Tests are typically performed on an entire structure, but large or complex buildings, or new additions to old buildings, may require isolating and testing portions of the building. During a test, the HVAC equipment is turned off with dampers closed, and equipment-related openings are temporarily sealed off (i.e., removing intentional holes from the equation).

What are the consequences of failing a test?

Because whole-building airtightness testing is completed towards the end of a building’s construction, it means that leaky air barrier components revealed in the test are difficult to repair, as they are typically covered by cladding or finishes. Obviously, getting it right the first time will save time and money when the project team is under pressure to get a certificate of occupancy. For example, the Seattle Energy Code requires completed buildings to achieve a maximum air-leakage rating of 0.25 cfm/ft2. If the air barrier test shows leakage greater than this but less than 0.40 cfm/ft2, the project team must conduct visual inspections, seal leaks where possible, and document corrective actions. If the tested leakage exceeds 0.40 cfm/ft2, the team must execute remediations and re-test, adding time and cost.

Beyond code compliance issues, falling short of airtight performance expectations can have other impacts. Leakage occurring in an isolated location can have serious consequences. We assisted a building owner to correct such a failure after a single point of air leakage caused a water pipe to freeze and burst, resulting in millions of dollars in damages. A broader failure attributed to a typical condition (e.g., wall to roof interface) may require significant removal and reinstallation of cladding materials to correct. Since a tight building enclosure can account for a 5% to 40% of energy savings in most of the U.S. (depending on climate zone), a project with a zero net energy/carbon goal may fall short and require the costly addition of more photovoltaic panels if air leakage targets are not met. A leaky air barrier can also result in condensation issues, microbial growth and poor indoor air quality.

What are best practices to ensure airtightness requirements are met?

The first critical step happens in the construction documents phase with a design review by a building enclosure professional. The review will verify that the design intent for a continuous air barrier is realized. The air barrier materials and assemblies should be clearly shown and labeled on all drawings, with continuity demonstrated at all penetrations, and assembly transitions and intersections. Part of the review is the “pencil” continuity test—can the air barrier be traced in the building section without lifting the pencil from the page? The review also confirms that all appropriate materials/assemblies required for continuous air control are included in the details and specifications and verifies the constructability of a continuous whole building air barrier.

The next step is submittal and shop drawing review. An experienced building science professional can spot material compatibility issues and help contractors to develop interface details for coordination between trades to ensure that air barrier continuity is maintained. Many air leakage failures occur at building enclosure interfaces (e.g., the “by others” notes on shop drawings). Construction site visits by the building enclosure specialist are also critical. These inspections focus on the proper execution of the continuous air barrier design intent, with special attention to interface details, and remediation recommendations for observed deficiencies. The specialist will typically facilitate and witness functional performance field tests of various building enclosure air barrier materials/assemblies and guide corrective action, if required.

In summary, building enclosure airtightness is the easiest energy efficiency measure to get wrong, and the hardest to connect after the fact. As infiltration reduction is critical to both energy code compliance and high-performance building performance, project teams should incorporate design reviews and construction phase site observations to promote a successful whole-building airtightness test the first time. Proactively including air barrier continuity as part of an overall quality assurance process will save time and expense and avoid building performance issues.

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Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 35 years of experience in sustainable building design. He is director of sustainability with Intertek Building Science Solutions in Portland, Ore. Ish Keener, SE, PE, is an engineer with 14 years of experience and a Senior Engineer with Intertek Building Science Solutions in York, Pa. To learn more, follow Alan on LinkedIn at www.linkedin.com/in/alanscottfaia/[1] and Ish Keener on LinkedIn at www.linkedin.com/in/ishkeener/[2].

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