Metal building systems make up nearly 40 percent of the low-rise, non-residential building market and are a popular choice for a variety of end uses. Their versatility, cost-effectiveness and sustainable features make them a smart fit for commercial, educational, religious and industrial facilities, as well as myriad other uses.
Metal building systems use steel, a non-combustible framing material, which often results in its overall classification by the International Building Code as Type IIB construction that does not require passive fire protection. Passive and active fire protection requirements are based on a combination of construction type and the end use, in addition to other factors. There are certain circumstances, however, where part or all of the building must have some form of fire protection due to its end use, storage commodity or proximity to other buildings on or near the property where the building will be situated.
The Metal Building Manufacturers Association, Cleveland, has undertaken extensive fire testing to demonstrate how metal building systems and components perform in certain situations and has developed code-compliant, fire resistance-rated design details.
Building Types and Code Requirements
The need for fire protection in metal buildings depends on several factors, including the end-use of the building, the size of the interior space, interior walls and separations, the number of stories or levels, distance to exits and the building’s proximity to other buildings and/or the property line. As a result, building codes may require parts, or all, of the building to have passive or active fire protection.
Active fire protection is defined as materials and systems that are activated by a fire for the purpose of suppression, warning, and/or other notifications intended to mitigate the fire hazard effects on the building occupants and minimize property damage. Automatic sprinklers, fire detectors and alarms all are examples of active fire protection devices. Passive fire protection encompasses materials and systems that provide thermal insulation and barriers to fire exposure on structural elements, and which do not require any external activation to function. Examples include gypsum board, spray-on fireproofing, and concrete or masonry materials.
Various parts of the building that may require passive protection include interior and exterior rated walls, ceilings, columns, floors and joints between fire-resistance-rated assemblies. Depending on what type of building it is, the fire protection can warn occupants of a fire, allow occupants time to safely exit a building, maintain the structural integrity of the building during a fire, and protect emergency responders as they attempt to control the fire. These needs often depend on the use and size of the building.
The International Building Code classifies buildings based on the intended occupancy, or end use. Occupancy classifications are designated by (A) Assembly, (B) Business, (E) Educational, (S) Storage and (U) Utility and Miscellaneous. The building occupancy classification has a direct bearing on the fire code requirements and the allowable height and area of a building.
The 2009 IBC delineates code requirements for specific situations for each building type, such as exterior separation from other buildings or the property line. For example, any building type and occupancy (including Type IIB) that has an exterior separation distance of less than 10 feet must have exterior fire-resistance-rated walls. As the distance between adjacent buildings increases, the required fire-resistance rating decreases until none is required. This varies by construction type, with non-combustible construction, like metal building systems, requiring less fire protection than combustible construction, such as wood. The IBC provides a complete set of charts and tables that presents the requirements for all building types and occupancy classifications.
Schools are classified as Group E occupancy. In 2009 IBC Table 503, a metal building system that is classified as Type IIBwithout fire protection ratingsis limited to 14,500 square feet per floor, for up to 2 floors, for a school or educational facility. With one-hour fire-resistive construction ratings, the building then could be reclassified as Type IIA such that the allowable floor area can be nearly doubled to 26,500 square feet with one more story level permitted up to three stories. Additional size increases are allowed with the incorporation of sprinklers, which is covered in Section 506 of the IBC (Area Modifications).
One-story, low-hazard storage buildings, classified as S-2 occupancy in the IBC, which are surrounded by public ways or yards of not less than 60 feet from other buildings, can have unlimited building area according to 2009 IBC Section 507.1, even without sprinklers. Other building occupancy types have similar size limits depending on the specific fire protection.
In order to make the rules clearer and demonstrate how metal building systems and the specific components meet the requirements, MBMA has sponsored fire tests at Underwriters Laboratories Inc., Camas, Wash., and Factory Mutual, Johnston, R.I. These tests have involved structural columns, interior and exterior walls, roofs and ceilings, sprinklers, and joints between walls and ceilings.
Head of Wall Joints and Fire Protection
The latest fire protection research undertaken by MBMA concerns the joints between fire-resistance-rated walls and non-fire-resistance-rated roofs. These intersections often are referred to as head-of-wall joints between the constructions, although the term “joint” actually is a misnomer. In the building code, a joint is formed when two fire-resistance-rated building components come together. When a non-rated assembly and a rated assembly come together, which is a fairly common occurrence in Type IIB construction, there isn’t a code-defined name for this intersection. Often, the requirements for fire-resistance-rated joints are mistakenly called out for these assemblies.
Although it is a very common occurrence, the building code is not entirely clear about the code requirements where a fire-resistance-rated wall meets a non-fire-resistance-rated roof deck. This situation often happens when the roof is more than 20 feet above the floor of the building, which is the point where the building code often allows non-fire-resistance-rated roofs. The Washington, D.C.-based International Code Council confirmed that the code does not require a fire-resistance-rated joint between the roof and wall. The ICC interpretation states that the code does require that the wall maintain continuity with the roof deck. By performing the testing at UL, MBMA confirmed that the proposed detail did maintain continuity during the testing.
The tests performed by UL included all the possible configurations of the wall intersecting the purlins in a metal roof: a purlin inside the wall, a purlin perpendicular to the wall and a purlin parallel to the wall. By evaluating these three configurations, the testing showed that the intersection of the non-fire-resistance-rated roof and the fire-resistance-rated wall maintained the code-required continuity of the wall to the roof. Complete specifications and details of the assemblies, tests and UL listings are available at www.mbma.com.
In the tests, the roof fiberglass insulation was draped over the wall, running continuously. In the past, building officials mistakenly have asked for the insulation facing to be cut and reattached on either side of the wall. Because the MBMA/UL testing was performed with the insulation continuously uncut over the wall, it showed that it is not necessary to cut and reattach the insulation. In other words, the insulation facing did not carry the fire over the top of the rated wall to the other side.
In addition to the non-rated roof testing, the UL program also created three new fire-rated joint systems, which have the UL designations: HW-D-0488, HW-D-0489 and HW-D-0490. These rated joint systems are applicable for situations where occupancy or ceiling height limitations would require a rated roof-ceiling assembly to be used in a metal building.
Code requirements and fire-resistance ratings can be confusing and questions often arise. The MBMA is working to provide answers and technical knowledge to help clarify these issues for professionals who design and construct buildings that incorporate metal building systems.
Metal Building Manufacturers Association
The Cleveland-based Metal Building Manufacturers Association promotes the design and construction of metal building systems in the low-rise, non-residential building marketplace. MBMA has conducted extensive fire testing and has published a series of fire resistance and insurance bulletins, available for free download at www.mbma.com under the Fire Resistance box on the home page. These resources can provide knowledge for builders, building officials and architects. The information contained in MBMA’s Fire Bulletins 1 – 4 detail fire performance and fire resistance ratings for various types of steel columns, roofs, ceilings, interior and exterior walls.
An additional forthcoming resource, MBMA’s Fire Resistance Design Guide for Metal Building Systems is due for publication this year. It will be a comprehensive resource for building designers, contractors and design professionals who are looking for answers to questions, as well as alternative design solutions. It also will potentially help them continue to expand the use of metal buildings into even more end uses.
Dan Walker, PE, is senior staff engineer for MBMA and Thomas Associates, both based in Cleveland. He can be reached at (216) 241-7333 or email@example.com.