Historically, membrane penetrations were treated as one-half of a through penetration firestop systems. Some model codes even included verbiage to this effect. Recently, UL announced that their requirement would be for membrane penetrations to be specifically tested and listed. They cited the fact that when the membrane penetration firestop system was tested for fire exposure to each side, they had concerns about whether the configuration where the gypsum board was intact on the backside of the penetration would behave the same way. While perhaps not a concern for noncombustible penetrants such as metallic pipe or conduit, it could be a concern for plastic pipe (See Figure for more detail). Accordingly, this has necessitated specific testing and listing of membrane penetration firestop systems. Look for more membrane penetration systems in the W-L-Series design from STI and others in the near future.

New UL^® Systems for Membrane Penetrations

• W-L-1527: Max 1” copper or 3” steel and iron pipes
• W-L-2635: Max 2” PVC pipe with sealant only
• W-L-2636: Max 3” PVC pipe with wrap strip tuck-in
• W-L-2637: Max 4” PVC pipe with wrap strip collar
• W-L-3427: Max 1-1/2” diam cable bundle
• W-L-5327: Max 1” copper or 2” steel pipe
  with max 2” thick fiberglass insulation
• W-L-7244: Max 2” x 6” dimensional lumber
• W-L-7245: Max 3-1/4” x 1-5/8” steel strut or max 2” x 2” steel angle
• W-L-7246: Max 5” diam steel duct