Commercial corridor ceilings need ratings for fire protection.
Corridor ceilings in commercial or office buildings require ratings for fire resistance. These ceilings must comply with the regulations of the Uniform Building Code. In many cases, installing two layers of gypsum board in the corridor ceiling allows the ceiling to comply with ratings, but local construction officials must inspect and approve the installation.
Terms
Fire resistance is the property of building materials to prevent or delay excessive heat passage or that of flames under fire conditions. A fire-resistance rating is the time period that any building component maintains the ability for fire containment or continues to perform its structural function during fire conditions. The UBC and the International Code Council have testing methods to determine fire resistance ratings. Minimal ratings are at least one hour of fire resistance.
Requirements
At a minimum for fire resistance, gypsum panels on the room side of the corridor walls extend to a corner, meeting to form an outside angle with the gypsum board layers on top of the ceiling. This ceiling is built as if it were a separate wall, placed completely on the corridor wall top so that the ceiling's lowest panel extends above the walls' top plates. Because creation of corner and head details may be open to interpretation, consult the local code official before corridor construction.
Obtaining a Corridor Rating
Obtaining an hourly rating for the corridor and its ceiling requires following standard industry practices during the construction process. If the walls of the corridor don't go to the deck, use the correct Underwriter's Laboratories design to put in the required fire resistant ceiling as well as a fire resistant grid in both the ceiling and surrounding areas. If the corridor's walls run to the above deck, find the Underwriter's Laboratories design for installation of the specific ceiling and grid. Where walls are penetrated, use fire-dampers to prevent fires from spreading through ductwork.
Testing
Commonly known as the tunnel test, the test used for ratings calculations is actually called the "Method of Test of Surface Burning Characteristics of Building Materials," by the National Fire Protection Association. The NFPA has not accepted alternative methods for determination of the characteristics of flame spread in buildings, although other ratings tests exist for product development purposes.
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