sprinklernotes
NFPA 13D Domestic Demand
You asked the following question: “NFPA 13D-2016 section 6.5.2 requires a 5-gpm
allowance to be added to the hydraulic calculation when the water supply serves
multiple dwelling units and the fire protection water is not separate from the
domestic. On this project there are seven townhouses attached to a common
combined (fire/domestic) 1-1/2 in. shared main. Is the requirement to add 5 gpm
to each building individually or a cumulative 35 gpm for all seven buildings
required?”
In response to your question, we have reviewed NFPA 13D, Standard for the
Installation of Sprinkler Systems in One- and Two-Family Dwellings and
Manufactured Homes, 2019 edition.
Our informal interpretation is that the 5-gpm demand needs to be added at each
connection to the common water supply accounting for incidental domestic use
during a fire event in one of the townhomes.
Per section 6.5.2:
6.5.2 In common water supply connections serving more than one dwelling unit, 5
gpm shall be added to the sprinkler system demand to determine the size of the
common piping and the size of the total water supply requirements where no
provision is made to prevent flow into the domestic water system upon operation
of a sprinkler.
This principle was first introduced in the 1996 edition of NFPA 13D with the
acceptance of public input 13D-7. In their statement, the committee said, “If
NFPA 13D is used in a multi-family environment, then the 5-gpm flow should be
added in at each additional point of connection.” The committee stated “each
additional point of connection” in their statement!
For one- and two-family homes, this would constitute a 5-gpm allowance and
limit; however, the standard did not consider townhomes (many one-family homes
grouped together) and their shared infrastructure. A single domestic fixture
can use up to 5 gpm and it would be difficult to halt domestic use in adjacent
units as they might not even be aware of the fire in another unit – NFPA 13
does not require an alarm. For the 2025 edition of NFPA 13D, AFSA intends to
submit public input to the residential committee to address the ambiguities in
this requirement.
