All About Attachment
Roof decks need to be adequately attached to underlying structural framing members to prevent wind uplift. With some designs, the attachment of the roof deck plays an important role in the roof deck “diaphragm” to resist horizontal loads and provide lateral bracing for the building’s structure.
Steel roof decks are typically attached to the underlying roof structure using welds or mechanical fasteners. SDI and FM Global provide two generally recognized but somewhat differing guidelines applicable to the attachment of steel roof decks. The most stringent fastening recommendations of SDI’s Design Manual for Composite Decks, Form Decks, and Roof Decks
or Diaphragm Design Manual
should be used.
FM Guidelines can be found In FM’s Loss Prevention Data Sheet 1- 29, Roof Deck Securement and Above-Deck Roof Components (dated 9/10), and reference data sheets 1-28R and 1-29R. If your building is insured by FM Global, they should be part of the decision process for reroofing or roof replacement.
Steel roof decks generally are considered to be nailable, or in the case of steel roof decks specifically, mechanically attachable. That is, steel roof decks generally require the installation of rigid board insulation prior to the insulation of the roof membrane.
Built-up, polymer-modified bitumen, and single-ply membranes are always installed on top of a rigid board substrate that’s either mechanically attached to the steel roof deck or loose-laid, depending on the roof membrane system.
NRCA does not recommend the use of low-rise foam or liquid-applied adhesive as the primary means of attachment of rigid board insulation to steel roof decks. If you’re using low-rise foam or liquid-applied adhesive to adhere rigid board insulation to steel roof decks, NRCA recommends that you obtain agreement from the adhesive, rigid board insulation, and membrane manufacturers regarding the appropriate adhesive type and its application rate.
Also keep in mind that the best class required by model building codes for a fire-resistant building is a B, not an A.
Looking to learn more? Chck out these resources:
- ANSI/Steel Deck Institute: RD-2010 Standard for Steel Roof Decks
- Steel Deck Institute Publication No. 31, Design Manual for Composite Decks Form Decks and Roof Decks
- NRCA Roofing Manual, CD-2011
- FM Global datasheets
- Approval Standard for Profiled Steel Panels for Use as Decking in Class 1 Insulated Roof Construction Class Number 4451, June 2012
- SEI/ASCE Minimum Design Loads for Buildings and Other Structures (7-10)
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