Metric Steel Decks

June 2004

Gypsum board and other panel type materials are widely used over steel decks in compact roof systems to provide a level base for the other components or to serve as thermal barriers. When installed onto the steel deck, good roofing practice requires that opposite sides of each board to be supported on steel deck flanges, as close as practical to the centre of the flange. Many of the roofing products used in Canada are sourced from the US and are sized in inch-pound (imperial) units. The most widely used gypsum based roof board is available in sizes of 4 ft. by 8 ft., and 4 ft. by 4 ft. Similarly, much of the corrugated steel roof deck used is also sized in imperial units, with standard widths of 2.5 ft. and 3 ft.

However, on occasion, metric sized deck is used. When this occurs, the edges of the gypsum or other panels may not align with the load bearing flanges of the deck in successive rows if they are sized in inch-pound units. This may necessitate the periodic trimming of boards so that the edges will be adequately supported. This can be a time consuming and costly process. When submitting their bids, contractors should specify that their estimates are based on the steel deck being of standard imperial dimensions and that there will be additional costs should metric sized steel deck be used.

The opinions expressed herein are those of the CRCA National Technical Committee. This Advisory Bulletin is circulated for the purpose of bringing roofing information to the attention of the reader. The data, commentary, opinions and conclusions, if any, are not intended to provide the reader with conclusive technical advice and the reader should not act only on the roofing information contained in this Advisory Bulletin without seeking specific professional, engineering or architectural advice. Neither the CRCA nor any of its officers, directors, members or employees assumes any responsibility for any of the roofing information contained herein or the consequences of any interpretation which the reader may take from such information.