Membrane roof systems serving as air barriers

Keeping the air barrier continuous
An air barrier needs to be installed continuously on all sides of a building. In order to achieve this, the wall air barrier should be sealed to the roof air barrier. Figures 3 to 5 are conceptual drawings to help illustrate a continuous air barrier at a parapet wall condition with a membrane roof system.

Figure 3 is where the wall air barrier is a membrane or coating system installed on the structural backup wall and the membrane roof system serves as the roof air barrier. In this example, the membrane roof system is sealed to the wall air barrier to keep the air barrier continuous.

Figure 4 is where an exterior insulation sheathing board serves as the wall air barrier. This type of construction is where a layer of ‘continuous insulation’ is desired on a wall system. In this example, the membrane roof system is sealed to the exterior insulation sheathing board to keep the air barrier continuous.

Figure 5 is where the wall cladding serves as the wall air barrier. In this example, the membrane roof system is sealed to the wall cladding to keep the air barrier continuous.

Conclusion
For new construction, it is the responsibility of the building’s design professional to determine the need for an air barrier and provide details on sealing joints, penetrations, and transition areas, as well as verify an air barrier’s compatibility with other materials.

Also, one must bear in mind that the opportune time to address air barriers is in the design and pre-construction phases of a project. In other words, the time to discuss air barriers is before construction begins, not during.

Joan P. Crowe, AIA, is manager of codes and regulatory compliance at GAF. Her responsibilities include monitoring building codes, standards, and regulations, providing technical assistance to the sales and marketing departments, and producing technical documents. She holds a BS degree in architectural studies and a master’s of architecture from the University of Illinois Urbana-Champaign. She can be reached at jocrowe@gaf.com.

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