WALTHAM, Mass. — SPRI has published a detailed Bulletin that includes recommendations for the design and contractor communities on important changes recently made to FM Approvals (FM) Standard 4470. The four-page Bulletin, an Excel worksheet and an executive summary are available for download at www.spri.org/publications/policy.htm.

On Oct. 18, 2012, FM officially notified roofing system manufacturers and component suppliers of the revised FM Approval Standard 4470 (FM 4470), “Single-Ply, Polymer-Modified Bitumen Sheet, Built-UP Roof (BUR) and Liquid Applied Roof Assemblies for use in Class 1 and Noncombustible Roof Deck Construction.” The effective date of the revised FM 4470 is Dec. 31, 2012. The notification letter and some details and anticipated changes can be found at www.roofnav.com.

The most significant changes made by FM Global to FM 4470 relate to steel roof decking and include the following, as stated by FM:

• “Stresses induced to steel roof decking shall be determined by rational analysis and shall not exceed the allowable stresses per the latest edition of the North American Specification for the Design of Cold-Formed Steel Structural Members, AISI S100-2001.”

• “Limits on roof deck fastener stress have also been added.”

In addition, FM will also conduct a full review of all current RoofNav Approved steel deck assemblies that, in its opinion, “overstress the deck.” See SPRI’s Bulletin for more details on the ramifications of FM’s new review process.

“It should be noted that FM Global/FM Approvals requires FM 4470 be used when FM insured buildings are having roof systems installed,” said SPRI Technical Director Mike Ennis. “Neither the existing nor revised FM Standard 4470 is a consensus standard that is included in the current International Building Code (IBC) editions 2009 and 2012.”

Because these changes are taking place before year-end, SPRI’s Bulletin includes recommendations for designers and contractors who may be currently designing or bidding on an FM insured project. The SPRI Bulletin also features key recommendations when designing buildings (including roofing systems) that are not FM insured.

“Neither FM Approvals nor FM Global has provided a transition plan or any guidance when incorporating these changes on FM insured roofing projects bid prior to these changes becoming effective on RoofNav,” said Ennis. “On non-FM insured projects, SPRI recommends that designers do not use the new FM 4470 as the basis for their specifications.”

FM Approvals has confirmed that it has no loss history with mechanically fastened single-ply membranes (8’, 10’ or 12’ wide panels) causing damage to the decking or structure. These mechanically attached systems, which have been tested for wind uplift performance at various accredited laboratories, will continue to be offered in the market place.

“SPRI encourages contractors to identify and comply with the IBC along with the designer of record and/or AHJ (Authorities Having Jurisdiction) specifications,” said Ennis. “When the building or tenant is FM insured, SPRI recommends that the appropriate FM field office be contacted prior to starting work to re-confirm acceptance of the roofing system to FM requirements.”

For more information, visit www.spri.org.