sprinklernotes
Combustible Concealed Spaces and the 3000 sq. ft. Design Area Increase
You asked the following question: “Can you use the 3,000 sq. ft. design area to
omit sprinklers in the concealed space in between floors on a hotel that is 5
stories? There are no fire/smoke barriers and no insulation. The attic will be
sprinklered. The floors are constructed of open web wood trusses.” In response
to your question, we have reviewed NFPA 13, 2016 edition as the applicable
standard. Our informal interpretation is a 3,000 sq. ft. design area cannot be
used to omit sprinklers from a concealed space.
The 3,000 sq. ft. design area per Section 11.2.3.1.5.2 cannot be used to omit
sprinklers from concealed spaces. This is because a design area is required to
be increased to 3,000 sq. ft. in certain circumstances due to the omission of
sprinklers in combustible concealed spaces. This is stated in Section
11.2.3.1.5.1:
When using the density/area or room design method, unless the requirements of
11.2.3.1.5.2 are met for buildings having unsprinklered combustible concealed
spaces, as described in 8.15.1.2 and 8.15.6, the minimum area of sprinkler
operation for that portion of the building shall be 3000 ft2 (280 m2 ).
This is also explicitly stated in the commentary for Section 11.2.3.1.5.1 in
the NFPA 13 Handbook. The NFPA 13 Handbook commentary states: “The intention of
11.2.3.1.5.1 is not to permit the omission of sprinklers from combustible
concealed spaces but, rather, to compensate for the anticipated delay of
sprinkler operation for a fire originating in an unprotected, combustible
concealed space. As noted, 8.15.1.2 describes the conditions under which
sprinklers do not have to be installed in concealed spaces.” Hence, before it
can be determined if the 3,000 sq. ft. design area is required by Section
11.2.3.1.5.2 we have to start by determining if sprinklers can be omitted in
the combustible concealed space, and for that we need to look at Section
8.15.1.1:
Concealed spaces of exposed combustible construction shall be protected by
sprinklers except in concealed spaces where sprinklers are not required to be
installed by 8.15.1.2.1 through 8.15.1.2.18 and 8.15.6.
Section 8.15.1.2 provides 18 conditions as subsections where sprinklers can be
omitted. Only one of the 18 conditions from Section 8.15.1.2 has to be met to
omit sprinkler. If Section 8.15.1.2 is met, at this point we can go back to
Section 11.2.3.1.5.1 to determine if a larger remote area can be avoided. From
here we have look at Section 11.2.3.1.5.2 to see if we can avoid the penalty of
increasing the design area for not sprinklering the combustible concealed
space. Section 11.2.3.1.5.2 give us 10 conditions where we are not required to
increase the design area. If any of the listed conditions are met the penalty
can be avoided. There are no situations in Section 8.15.1.2 for this
arrangement that we can apply with the information provided. Now if you had
qualified to omit sprinklers, Section 11.2.3.1.5.2 would have applied and could
force you to pay the penalty of larger design areas on multiple floors if rated
construction is not provided.
Again, the intention of 11.2.3.1.5.1 is not to permit the omission of
sprinklers from combustible concealed spaces. Rather, it is to compensate for
the anticipated delay of sprinkler operation for a fire originating in an
unprotected, combustible concealed space as well as the potential for the fire
to break-out in multiple locations.
