(CLICK CHART TO ENLARGE) Air leaks are ranked on the basis of CFM50 reduction for the amount of effort required, and the amount of material needed, to complete each air-sealing task. Owens Corning grouped the results in three categories: those that provide a “big bang for a builder’s air-sealing buck” (red); those that provide a “medium bang” (orange); and, as the return tapers off, those that provide only a “small bang” (green). Certain leaks—like vertical sheathing joints and the sheathing joints around windows and doors—required a lot of sealant for only a modest reduction in airflow, which is why they are “small bang” leaks.

Photos: Courtesy Owens Corning

(CLICK CHART TO ENLARGE) Air leaks are ranked on the basis of CFM50 reduction for the amount of effort required, and the amount of material needed, to complete each air-sealing task. Owens Corning grouped the results in three categories: those that provide a “big bang for a builder’s air-sealing buck” (red); those that provide a “medium bang” (orange); and, as the return tapers off, those that provide only a “small bang” (green). Certain leaks—like vertical sheathing joints and the sheathing joints around windows and doors—required a lot of sealant for only a modest reduction in airflow, which is why they are “small bang” leaks.

Tough new energy codes will soon force even reluctant builders to pay more attention to air-sealing. The 2012 International Energy Conservation Code (IECC) requires blower-door testing and a visual inspection to ensure that a home is as airtight as possible. In addition, air-sealing requirements have gotten much stricter: In climate zones 1 and 2 (hot and humid zones), a house needs to reach a 5 ACH50 threshold, down from 7 ACH50. In all other climate zones, homes need to reach 3 ACH50. So far, five states have adopted the 2012 IECC or an equivalent energy code: It’s law in Maryland and Illinois, and it becomes effective in California, Washington, and Massachusetts in 2014. At least 16 additional states will adopt the 2012 IECC or an equivalent by the end of 2015, according to a recent article in the Journal of Light Construction.

If done well, air-sealing has a positive impact on occupant comfort, energy efficiency, and indoor air quality, but it also can add to the cost of a project in labor and materials. To help builders facing new codes, Dave Wolf, senior research and development project leader at Owens Corning Science and Technology, set out to prioritize the leaks in a house by ranking which ones have the biggest impact on air infiltration. Acknowledging that many builders have a limited budget for air-sealing, his goal was to identify the leaks that would give a builder the most “bang for his air-sealing buck.”

With nearly a mile of joints on a typical house that connect the inside to the outside, Wolf’s research was no small task. After completing studies in a research lab and a test house, Wolf determined the top five areas in a home that will provide the biggest return on air-sealing investment. They are:
—recessed lights
—duct boot
—top plate to drywall at attic
—garage wall
—band joists

Wolf also found that leaks such as vertical sheathing joints and the sheathing joints around windows and doors require a lot of sealant for only a modest reduction in airflow. Read more free and premium content at JLC Online.

AIR-SEALING RESOURCES
For anyone air-sealing homes, here are some essential resources:

--Must-reads from past Journal of Light Construction articles:
“Blower Door Testing”
“Practical Details for Energy Efficiency”
• “Air-Sealing for Hot Climates”
• “Air-Sealing Tips and Tricks”

—Energy Star's Thermal Bypass Checklist Guide focuses on requirements for building an Energy Star home, including do's and don’ts for sealing common building-envelope air leaks.

—NYSERDA offers an interactive module that walks building officials through the criteria for visual inspection, which is mandatory under the 2012 IECC.

Building Science Corp. offers tons of free building-science resources. Joe Lstiburek’s article “Just Right and Airtight” is an important read that focuses on essential air-sealing principles.

—The Energy Vanguard blog translates difficult building-science topics into plain language for all. For folks working on existing homes, the post “The 3 Rules of Air-Sealing” provides clear guidance on retrofit air-sealing.

The Musings of an Energy Nerd blog by Green Building Advisor's Martin Holladay provides practical information relating to all things green building.