01 May 1999
the Underwriters Laboratories Roofing Materials and Systems Directory, the Factory Mutual
Approval Guide, and reports/directories published by several other qualified testing agencies.
a/ If a roofing assembly fails to meet burn-through requirements of ASTM
E108 it may still be listed for use with non-combustible decks such as steel, concrete, and
b/ Roofing assemblies are listed at the maximum incline to which the rating
applies. As long as the structure under consideration is at a lower or equal incline to that listed it
complies with the fire rating.
c/ If a listing is intended for use as a roof superimposed over an existing
roof, it should be listed in the UL Roofing Materials and Systems Directory under the category
Maintenance and Repair Systems. In the FM Approval Guide it will be listed as a Re-cover.
d/ In general, only the materials listed qualify and only when used in the
manner described in the directories. Additional insulation, for example, might worsen the flame
(b) An internal (underdeck) fire is when the flame spread is underneath the roof
deck. Listings are referred to by the Approval Rating, usually Factory Mutual Class 1 or
Underwriters Laboratories Insulated Metal Deck or Non-metallic Decks Constructions.
1/ Background--In 1953, a large insulated steel roof deck building suffered an
unexpected, catastrophic fire loss due to an underdeck fire exposure. The roofing components
above the deck contributed fuel to spread the fire. Tests conducted on full scale test buildings
confirmed the hazard. In the late 1950's, laboratory tests were established and correlated to the
full scale data. Factory Mutual uses a calorimeter to establish fire performance while Underwriters
Laboratories uses a modified Steiner Tunnel test. Successful systems are listed by FM as Class 1
while Underwriters lists them as either Rated Metal Deck or Rated Non-Metallic Assemblies.
2/ The underdeck ratings do not assure zero risk. The ratings assume an
acceptable risk assuming normal fire detection and fire control procedures are available. If an
insulated steel deck system fails to comply with the requirements of FM Class 1, it is designated
Class 2. Class 2 constructions may be converted to Class 1 by the addition of underdeck
fireproofing. Class 2 constructions may also be acceptable if an approved sprinkler system is
(c) Fire endurance tests. These are time-temperature tests (ASTM E119) in which
the roof-ceiling assembly is subjected to a rising heat load until either the interior structural
elements yield, or the temperature on the exterior roof system reaches 139oC (250oF) above the
1/ The minimum elapsed time required before the end point is reached is
usually established by building code or occupancy (e.g., 1-hour, 1-1/2 hour, etc.).
2/ Rated assemblies are listed by UL in their Fire Resistance Directory and by
FM in their Approval Guide. Other testing agencies list rated assemblies in their directories as
(d) Assure that fire compliance (ratings) pertain to the entire assembly. Each
component of the system must be listed in the above directories. Materials delivered to the job
site should bear labels indicating compliance with the construction intended. The label also