Specifying grease ducts using new codes

Grease duct system codes will change dramatically in January 2009. These changes are far-reaching and affect architects, engineers, specifiers, and contractors. The changes, if not recognized and addressed from the beginning of a project, could cause widespread confusion and, in some instances, major redesign, delays, or additional costs.

In January, Underwriters Laboratories (UL), Intertek Systems, and the International Code Council (ICC) Evaluation Services jointly are abandoning all listings or evaluations that are based on Southern Building Code Congress International Inc. (SBCCI) and Building Officials and Code Administrators (BOCA) acceptance criteria, both of which use the internal fire test portion of UL1978, which addresses reduced clearances for field applied flexible wrap systems.

Once abandoned, the only listing for flexible wraps applied to grease ducts will be ASTM E2336-04.

For non-fire-rated grease duct applications (grease ducts that do not penetrate a fire partition), any edition of any code requiring a “listed” product to reduce clearances can only allow flexible wraps installed in compliance with ASTM E2336-04. Factory-built systems listed to UL1978 for reduced clearances are not affected by this change, and may be used in installations where a fire-resistive enclosure is not required. The referenced codes are: 2006 International Mechanical Code (IMC) — Section 506.3.1.1 Exception, 2004 NFPA 96 — Section 4.2.2, and 2006 Uniform Mechanical Code (UMC) — Section 507.2.1 Exception 1.

Single-wall factory-built grease ducts will not be allowed to be enclosed or wrapped with one or more layers of flexible wrap material unless the factory-built grease duct listing and the flexible wrap manufacturer’s listing clearly states such system has been evaluated to UL1978. This is not a new development based on changes to the national codes. The UL guidelines for UL1978 test standard are clear on this issue, and code officials having jurisdiction should be aware to limit liability of a nonlisted system that results from combining the two products.

UL2221, “Tests of Fire Resistive Duct Assemblies,” and ASTM E2336-04, “Standard Test Methods for Fire Resistive Grease Duct Enclosure Systems,” are the standards applied to alternative construction methods for fire-resistive shafts. These codes are: 2006 IMC — Section 506.3.10, 2004 NFPA 96 — Section 4.3.1, and 2006 UMC — Section 507.2.3.

Compliance with these standards provides an enclosure that is rated at 0 in. clearance to combustibles. When penetrating a fire-rated partition, the penetration must be fire stopped to the rating of the partition.

Effective January, all flexible wraps must be applied in accordance with ASTM E2336 where code specifies a product listed to a nationally recognized standard. All other acceptance criteria and regional or nationally recognized approvals are abandoned. Factory-built systems must comply with UL2221 when used as an alternative shaft enclosure with 0 in. clearance to combustibles. Factory-built systems can continue to be installed per their listings for reduced clearances to combustibles as listed in UL1978 where a fire-resistive enclosure is not required.

Code history

Since 2000, quiet, yet significant changes have been made to the codes governing the installation of grease ducts for commercial kitchen applications. There are three major code bodies: the NFPA; the IMC, part of the family of codes developed by the ICC; and the UMC, a part of the International Assn. of Plumbers and Mechanical Officials (IAPMO) code set. These model codes specify standards and listings developed by independent testing groups such as UL and ASTM International.

Basic construction of grease ducts serving Type I hoods require 16-gauge carbon steel or 18-gauge stainless steel. The referenced codes are: 2006 IMC — Section 506.3.1.1, 2004 NFPA 96 — Section 7.5.1, and 2006 UMC — Section 510.5.1.

Both types of construction require a minimum of 18 in. of clearance to combustibles when unprotected. The referenced codes are: 2006 IMC — Section 506.3.6, 2004 NFPA 96 — Section 4.2.1, and 2006 UMC — Section 507.2.1.

For grease duct applications that do not require a fire-rated system, but do come within closer proximity to combustible materials, the codes allow for means to reduce the minimum air space between grease duct and combustible: 2004 NFPA 96 — Section 4.2.3 and 2006 UMC — Section 507.2.1 Exception 2.

Initial protection, where structural or other considerations did not allow room for clearances, was provided by a fire-rated shaft enclosure as defined in model building codes. A one-hour fire-resistive shaft is constructed of a single layer of fire-rated gypsum board applied to both sides of metal studs in the manner described by the building codes. Two-hour rated shafts require an additional layer of fire-rated gypsum board.

Proper construction of fire-resistive enclosures was very time-consuming, especially where offsets were required. In the early 1990s, SBCCI created the first alternative fire-resistive enclosure test criteria based on ASTM E119, ASTM E814, and the internal fire test section of UL1978 “Test Standard for Grease Ducts.” Flexible wrap systems were tested to the model code acceptance criteria, and regional acceptance of these systems was achieved.

Soon after, BOCA and the International Conference of Building Officials evaluation services created their own separate acceptance criteria for evaluating alternative fire-resistive systems as pertaining to kitchen exhaust. Flexible wrap systems were tested to these model code acceptance criteria and, as a result, achieved national acceptance as an alternative to a code prescribed fire-rated shaft protecting a welded grease duct.

As early as 1994, several manufacturers introduced factory-built grease duct systems composed of completely assembled components designed to easily connect in the field for complete systems. Standard UL1978 provides reduced clearances to combustibles and evaluates nonwelded joints as in compliance with NFPA, ICC, and IAPMO requirements.

UL1978 does not evaluate fire-resistive enclosures or building materials. It is used solely for factory-built ducts that are completely assembled in the factory, listed and labeled, and subject to periodic inspections by the listing agency to ensure materials and final construction are equivalent to the products tested per the UL1978 standard. Clearances must be displayed on the UL label and installed in accordance with the clearances specified. UL1978-listed grease ducts must be installed per the manufacturer’s installation instructions that meet the minimum requirements of the standard.

AT A GLANCE

In January, the major code bodies are abandoning all listings or evaluations that are based on SBCCI and BOCA acceptance criteria, both of which use the internal fire test portion of UL1978, which addresses reduced clearances for field applied flexible wrap systems. Once abandoned, the only listing for flexible wraps applied to grease ducts will be ASTM E2336-04. For more information, visit

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