This Building America Expert Meeting was conducted by the IBACOS team on Sept. 29, 2014, and focused on air sealing of area separation wall assemblies in multifamily buildings. This is an identified barrier that limits the ability of builders to cost effectively achieve higher energy efficiency and quality levels in multifamily housing. Air leakage through these assemblies is also a barrier to achieving air leakage limits mandated by the IRC and IECC. There is a need to engage with relevant stakeholders to develop a reasonable least-cost approach for the methods and materials of air sealing these assemblies.

For example, fire blocking sealants approved for use to seal framing penetrations within a dwelling are not allowed to be used to seal the perimeter of the 3/4” air space required in UL 263 (also ASTM E119) area separation walls. This unsealed perimeter condition makes these walls porous to airflow coming from the exterior or from attached garages. It is reasonable to ask if fire rated foam at that location would be better than allowing air leakage to feed the fire instead? The UL 263 tested condition was with the wall in a frame which completely sealed the end condition against air leakage and airflow at the end condition was not evaluated. Therefore, the tested condition does not well represent the field condition where the walls leak air at the perimeter and there is no approved method or material to seal them according to the typical U336, U347, and U373 Designs. Going further, area separation walls are also leaky across the wall to adjacent units. So even if the perimeter condition could be air sealed, that would not stop the problem of air leakage between dwelling units. It is reasonable to ask why a layer of paperless gypsum could not be installed on the fire rated side of the protected dwelling stud wall, while still maintaining the ¾” minimum air space between the dwelling wall gypsum and the area separation wall gypsum. This would allow interior-side air sealing and compartmentalization of the dwelling stud wall, in the same way that exterior walls are air sealed. In effect, this would gain control of the pressure boundary on all six sides of the attached dwelling unit as if it were an unattached unit. It may be possible that an option in the U347 Design, which does not exist in the U336 and U3737 Designs, may allow such gypsum sheathing to fully enclose the dwelling unit frame wall.

This forum brought experts and industry stakeholders together to discuss these issues and share information. Industry stakeholders may be energized to seek new UL evaluation reports. Short of that time and expense, approvals may be obtained through individual meetings with local code jurisdictions, but the ICC code change process may be the most efficient avenue.