Q.: We have installed a metal deck for a roof system on which the engineer has specified a lightweight concrete composite system. We have installed a vented metal decking, but the engineer has requested that solid metal decking be used. With lightweight concrete should the deck be vented or unvented for the best results?

A.: While we could't find anything specifically on the use of vented metal decking, we did do some research a year ago that showed that lightweight concrete can take much longer to dry (6 months versus 6 weeks for normal-weight concrete). The venting would help with this situation, allowing the deck to dry much faster. Otherwise we don't see how the vented decking would be different than solid, assuming it has the same strength properties (which is, of course, up to the engineer). If readers have more information, we will publish your comments in future issues.