sprinklernotes Supporting Multiple Pipes from a Single Trapeze Hanger Assembly
You have asked the following question: “I want to use a single trapeze member to support multiple mains. Section A.9.1.1.7 says that the required section modulus can be added to determine the trapeze size. This section does not mention any limit. I would like to use a 2½ in. by 2½ in. by 3/16 in. angle spanning four feet to support two 6-inch mains, a 4-inch main, a 2½-inch main and a 2-inch main. Is it the intent of NFPA 13 to allow the addition of the required section modulus with no limit as to how many mains can be supported as long as the available section modulus is not exceeded? In addition, Section 9.1.1.7.5 says that all components shall be sized to support the suspended sprinkler pipe. So, with the above scenario, would ½inch rod attaching the trapeze to the structure meet the requirements of NFPA 13 for trapeze hangers per Table 9.1.2.1? It would seem that if a trapeze was utilized to support multiple 6-inch mains that the attachments to the structure would need to be larger than ½-inch?” In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is the responses to the multiple questions are below. It is the intent of Section A.9.1.1.7 to allow the addition of the required section modulus with no limit as to how many mains can be supported as long as the available section modulus is not exceeded. However, Section A.9.1.1.7 is located within Annex A, thus is not a requirement within NFPA 13. The information provided within Annex A is a recommendation or explanatory material. With this in mind this topic should be discussed with the local AHJ and a written agreement with this interpretation should be obtained (or at least an email sent to the AHJ identifying the outcome of the discussion) before proceeding further with the project. To further complicate the matter, Table 9.1.2.1 only provides hanger rod sizes for a single pipe up to 12 in. in diameter. There is no information provided in Annex A for Section 9.1.2.1 or Table 9.1.2.1 for what to do when multiple pipes are supported by one hanger assembly. With this being the case one can assume that multiple pipes up to an equivalent diameter of those listed in Table 9.1.2.1 can be hung using the hanger rode sizes listed in Table 9.1.2.1. This limits hanger assemblies to one 12 in. pipe or multiple pipes that are equivalent up to one 12 in. pipe. Keep in mind that Section 9.1.2.2 allows hanger rods of smaller diameter than listed in Table 9.1.2.1 to be used when a hanger assembly has been tested and listed by a testing laboratory and installed per the listing of the hanger assembly.
