b'the membrane may have the performance characteristics toDesigners should specify or require preconstruction accommodate large-size tributary uplift loadingthe concen-trated line loads imposed on steel roof decks are different from those typically assumed in uniform load applications. submittal of membrane sheet layouts to ensure lines When rigid board insulation is attached to a steel roof deck with mechanical fasteners at a spacing of one per four square feet or less, any uplift load is assumed to be uniformly applied to theof fasteners comply with the designers assumptions. steel roof deck. Similarly, with an adhered membrane roof sys-tem, the membrane is adhered to underlying insulation, which is attached to a steel roof deck in a uniform load manner.With a seam-fastened membrane system, membrane seam fasteners apply wind-uplift loads to a steel roof deck as a series of line loads. In high wind and design wind load conditions, these concentrated line loads may exceed the uplift capacity of the steel roof deck and its connections to underlying supports.SDI recommends steel decks and their attachments be de-signed using AISI S100-16, North American Specification for the Design of Cold-Formed Steel Structural Members, and ANSI/SDI RD-2017, Standard for Steel Roof Deck.For seam-fastened, mechanically attached single-ply mem-brane roof systems, SDI considers the additional following guidelines to reflect generally accepted design practices:Analyzing the deck as a continuous three-span beam, unless shorter spans are usedUsingallloadcombinationsrequiredbythe applicable codeFor design spacing of fasteners lines, placing the first uplift line load at the midspan of the first deck span, then continuing to add line loads based on mem-brane seam spacingFordeterminingmaximumupliftondecksecure- CAN YOUment fasteners and support framing, placing a line load atop a supportSDI also offers the following recommendations: SPOT THE For seam-fastened systems, SDI recommends a struc-tural engineer review the adequacy of steel decks andLEAK?structural supports. In reroofing situations, SDI rec-ommends a competent structural engineer be en-gaged to determine any limitations imposed by anILD can, existing steel roof deck.Designers should specify or require preconstructionall of them.submittal of membrane sheet layouts to ensure lines of fasteners comply with the designers assumptions. Membrane seam attachment should only be perpen-dicular to the ribs of a steel roof deck; membraneIt takes an exceptional technician to nd every seams should not be attached parallel to deck ribs. leak in a green roof membrane. To weed out SDIstechnicalnoteincludessixappendicesprovidingthe false positives, to isolate the exact location. useful design analysis examples. These examples also illustrateILD is renowned for its expertise on green the magnitudes of the loading differences between uniformlyroofs. We nd breaches that others dont,distributed and concentrated line-load conditions. and we do the job right the rst time.Closing Thoughts SAVE YOURSELF SOME GREEN.Seam-fastened, mechanically attached, single-ply membraneCALL ILD FIRST. systems present unique wind-uplift loading considerations.Althoughthedesignofsteelroofdecksisbeyondthe expertise and responsibility of single-ply membrane manu- THE ORIGINALfacturers and suppliers, roofing contractors and most roofAND STILL THE BEST.system designers, you should be aware, in general, of these considerations. Toll Free: 1.866.282.5325 Mark S. Graham is NRCAs vice president of technical services. info@leak-detection.comThis article was originally published in the January 2020 issue of Professional Roofing magazine and is reprinted with permission from the National Roofing Contractors Association. ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 4 2019/202017'