BayPointArchitect
Sawhorse
Given:2009 IBCFour story apartments = R2 occupancy.Fully sprinkled 13R.1 hour fire-rated ceiling assembly.Several penetrations are located within the ceiling membrane. Floor decks are 3/4" gypcrete over 3/4" plywood. The ceiling consists of 5/8" Type "X" gyp.bd. attached to resilient channels = altogether a 1 hr. fire-rated assembly. Duct penetrations are limited to no more than 6" diameter. Ceiling radiation dampers are installed at each and every supply diffuser. However, some of these small 6" supply ducts extend from the main supply trunk line located below this drywall ceiling and then penetrate into this ceiling membrane. After the penetration, the HVAC Contractor and Mechanical Engineer would like to use flex duct throughout the floor truss system.Where a cluster of four 6" diameter penetrations are together (29 square inches each), then one of those four penetrations are protected with a damper so as not to exceed the combined 100 square inches maximum allowable within any given area of 100 square feet. A few ceiling electrical boxes will need to be UL rated for this reason also.Question:Am I interpreting Chapter 7 correctly by requiring that the material used for these small supply ducts to be limited to 1) steel, 2) copper, 3) concrete, or 4) masonry as indicated by the list of specified materials? Although one could argue that plastic is "non-combustible", I am thinking that a plastic flex duct would be acceptable if only it were part of a tested and classified UL assembly.See attachment.Thanks!ICC Certified Plan ReviewerNFPA Certified Fire Plan Examiner
View attachment 2031
713-MembranePenetration.pdf
713-MembranePenetration.pdf
View attachment 2031
713-MembranePenetration.pdf
713-MembranePenetration.pdf