October 17, 2016


Remote Area for Unprotected Concealed Combustible Space


“We have an NFPA 13 system that contains combustible concealed spaces formed by 
solid wood joists. Some of the spaces have been protected as a light hazard 
occupancy using upright, extend coverage sprinklers. Some of the concealed 
spaces have a ceiling attached to the joists and meets the allowance in Since this is an allowed omission of protection, am I required to 
apply the requirement for a 3,000 sq. ft. remote area by If 
applied, must all the allowances be applied concurrently, how is the 3,000 sq. 
ft. applied in conjunction with other modifiers, and what density applies to 
the design basis?”


We have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal 
interpretation is below.


Allow me to start with the bad news. An extended coverage sprinkler cannot be 
used with combustible, obstructed construction as dictated by 8.4.3. Generally 
speaking, extended coverage can be used only with smooth ceilings unless listed 
otherwise and that’s limited to noncombustible, obstructed construction. There 
is an allowance in 8.4.3(6) for their use when installed in every bay that is 
then treated as a smooth ceiling between the structural members.


As for the concealed spaces, all combustible concealed spaces must be protected 
unless they meet one of the 15 allowances identified in 8.15.1. When a 
concealed space is allowed to be unprotected, you then have to go to section to determine whether you have to increase the size of the remote to 
3,000 sq. ft. for the system adjacent to the unprotected concealed space. There 
are 10 allowances whereby the larger area does not apply. Allow me to emphasize 
that applying the 3,000 sq. ft. remote area does not allow omission for spaces 
not identified in 8.15.1. So returning to your particular case, 
allows spaces with ceilings within 6 inches of wood joists to be unprotected. 
Another nuance is that this application of wood joists does not include 
composite wood joists as discussed in A.3.7.1(3) and (6). The two are treated 
as individual types of structural members due to how quickly the web burns 
through on the composite wood joists. Going to Chapter 11, you also are not 
required to increase the size of the remote area since 
addresses this assembly. This section has been complicated by combining two 
situations into one allowance but focus on the specific statement on the 
ceiling attached directly to the bottom of the solid wood joist. I assume the 
volume of the channel is less than 160 cu. ft. (which is not a requirement for 
omission of protection). Also note the increased area would apply if the 
ceiling were up to 6 inches below the joists as allowed by


Although worded awkwardly, saying “unless the requirements of are 
met” does not mean that all of them are applied concurrently but that any one 
of them applies. Otherwise, it would say must comply with all of the 
requirements. Additionally, if the 3,000 sq. ft. remote area is applied, it is 
the final area after all modifiers are applied as stated in  
There is also no specified density but simply a minimum size. For instance, for 
a light hazard occupancy classification with no modifiers, you can apply a 
density of 0.07 gpm/ sq. ft. over 3,000 sq. ft. in accordance with Figure





Technical Update is prepared by the Technical Services Dept. of the AFSA: 
Roland Huggins, a PE registered in fire protection engineering, Vice President 
of Engineering and Technical Services; and Tom Wellen, a PE registered in fire 
protection engineering. This is provided with the understanding that the AFSA 
assumes no liability for this opinion or actions taken on it and they are not 
to be considered the official position of the NFPA or its technical committees.


Copyright 2016, American Fire Sprinkler Association. All Rights Reserved.

Ada Dickson
Ada Dickson
Administrative Assistant
Technical Services Dept.
 PH: (214) 349-5965 ext. 124   Fax: (214) 343-8898
E-mail: adick...@firesprinkler.org

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