Code Clarification: Membrane Penetrations in a Horizontal Assembly

The recent adoption of the 9th edition of Massachusetts Building Code, which is an amended version of the 2015 IBC, brings with it the addition and clarification of a commonly used construction practice regarding membrane penetrations in horizontal assemblies. The recently adopted code includes a new exception to Section 714.4.2 which states that the “ceiling membrane of both 1- and 2-hour fire-resistance-rated horizontal assemblies is permitted to be interrupted with the double wood top plate of a wall assembly that is sheathed with Type X gypsum wallboard”, provided that penetrations are adequately sealed and the ceiling membrane is tight to the top plates.

This assembly is a common occurrence in construction, but the design was not previously addressed in the code. In conventional framing, membrane penetrations are created where the top wall plates intersect the floor joists. This is now clarified and permitted in the code, but specifies that the wall is required to have two wood top plates and sheathed with Type X gypsum board. The assembly specified in the code is shown at left.

[Image from: Significant Changes to the International Building Code, 2015 Edition (ICC)]