Editor's note: The following article represents the experiences of the author, not necessarily those of NRCA or Professional Roofing magazine.
The old Factory Mutual (FM) system that transformed itself into FM Global has long been proactive in developing criteria for roof system evaluation through its research division, now called FM Research. FM Research started out as a nonprofit arm of the FM system to evaluate the performances of many construction materials and systems, including roof systems and roof components, and assist FM's underwriters in adjusting insurance rates for its insureds.
With the transformation to FM Global came some other changes. FM Property Loss Prevention Data Sheets became FM Global Property Loss Prevention Data Sheets, and the FM Approval Guide now is published by FM Global Technologies LLC. Although the original intent was to provide in-house information to the FM system, FM recommendations have permeated every nook and cranny in the roofing industry and indirectly affect every roofing contractor who deals with FM Global insureds and anyone who subscribes to FM Research recommendations. The yet-to-be-introduced RoofNav computer program being developed by FM Research is supposed to replace its Approval Guide and provide up-to-the-minute information about FM Research-approved roof systems and roof system components. RoofNav promises to be a significant challenge for roofing contractors.
The Approval Guide probably is the least user-friendly, most misunderstood, basically unreadable document ever published. But RoofNav is supposed to resolve these issues. The Property Loss Prevention Data Sheets are much more understandable than the Approval Guide but usually fail to provide the information necessary to install roof systems in some configurations. For example: The only reference in Property Loss Prevention Data Sheet 1-29 to mechanical attachment of a base sheet is over a wood deck 3/4 of an inch (19 mm) thick or thicker using large-head (1-inch- [25.4-mm-] diameter) roofing nails. There is no recognition for fastening of base sheets to cementitious wood fiber decks, poured-in-place gypsum or gypsum planks, or lightweight insulating concrete decks (and no differentiation between perlite or vermiculite aggregate lightweight insulating concrete and lightweight insulating cellular concrete) even though it is certain FM Global covers insureds with these types of roof decks in their inventories. There is no differentiation between base-ply fasteners with 1-inch- (25.4-mm-) diameter heads and base-ply fasteners incorporating FM Research 1-90 stress plates even though common sense would suggest a 3-inch- (76.2-mm-) diameter 1-90 stress plate should increase the uplift properties of base sheets over those of base sheets secured with 1-inch- (25.4-mm-) diameter heads and allow installation of fewer 1-90 fasteners for given uplift specifications.