sprinklernotes Combustible Concealed Spaces You asked the following question: If a design meets the intent of section 8.15.1.2.6 and sprinklers can be omitted because space is under 6 in., does the design area still need to be increased per section 11.2.3.1.5? In response to your question, we have reviewed NFPA 13, Standard for the Installation of Sprinkler Systems, 2016 edition. Our informal interpretation: The requirements of section 8.15.1 pertain to the omission of sprinklers in concealed spaces. When sprinklers are omitted in concealed spaces, the adjacent design areas are required to be increased to a minimum area of 3000 ft2 unless one of the ten (10) scenarios in section 11.2.3.1.5.2 are met. In this case, sprinklers are omitted in accordance with section 8.15.1.2.6: 8.15.1.2.6* Concealed spaces formed by ceilings attached to composite wood joist construction either directly or onto metal channels not exceeding 1 in. (25 mm) in depth, provided the joist channels are firestopped into volumes each not exceeding 160 ft3 (4.5 m3) using materials equivalent to the web construction and at least 3½ in. (90 mm) of batt insulation is installed at the bottom of the joist channels when the ceiling is attached utilizing metal channels, shall not require sprinkler protection. Per section 11.2.3.1.5: 11.2.3.1.5.2 The following unsprinklered concealed spaces shall not require a minimum area of sprinkler operation of 3000 ft2 (280 m2): (10)* Light or ordinary hazard occupancies where noncombustible or limited-combustible ceilings are attached to the bottom of composite wood joists either directly or on to metal channels not exceeding 1 in. (25 mm) in depth, provided the adjacent joist channels are firestopped into volumes not exceeding 160 ft3 (4.5 m3) using materials equivalent to ½ in. (13 mm) gypsum board, and at least 3½ in. (90 mm) of batt insulation is installed at the bottom of the joist channels when the ceiling is attached utilizing metal channels.
While there is similar language in sections 8.15.1.2.6 and 11.2.3.1.5.2(10), it is important to note that they are not exact carbon copies. In order to be relieved from the 3000-ft2 remote area requirement, the ceilings attached must be non- or limited-combustible, and the occupancy of adjacent spaces must be light or ordinary hazard. In addition, the firestopping materials in section 8.15.1.2.6 are permitted to consist of materials equivalent to the web construction (i.e., wood), but to not increase the remote area the materials must be upgraded to a gypsum board equivalent in order to contain the spread of fire to the 160-ft3 volumes (See A.11.2.3.1.5.2(10)). All of these items are in addition to the requirements of section 8.15.1.2.6.
