sprinklernotes
NFPA 13D Systems in Townhomes
You have asked the following questions: “We would like clarification on how
6.5.2 applies to buildings with two or more residential units that are served
by a single meter, with a supply that tees to each unit separately. Each unit
would have an individual sprinkler system, with no interaction between units
after the supply tee: Does the additional 5 gpm required by NFPA 13D 6.5.2
still apply in this situation? If so, does NFPA require 5 gpm for the full
project, or 5 gpm for each additional unit after the first? Additionally, NFPA
13 and 13R require sprinkler calculations to account for domestic demand in
accordance with NFPA 13R Table A.9.6. In a situation like the above, when
calculating the sprinkler system in one unit, are we required to include the
domestic demand for all additional units?” In response to your question, we
have reviewed NFPA 13D, 2016 edition as the applicable standard. Our informal
interpretation is that a sprinkler system for more than one dwelling unit will
require an inclusion of only 5 gpm for domestic demand.
Despite the fact that NFPA 13D is specifically developed for one-and two-family
dwellings only, the IRC or International Residential Code in section R313.1.1
tells us it’s acceptable to use NFPA 13D in townhomes with no quantification of
number of units. Section 6.5.1 indicates that where common supply pipes serve
both fire sprinkler and domestic use, they shall comply with 6.5.2 and 6.5.3.
Section 6.5.3 deals with a water treatment and filtration system that is not
applicable to your question. Section 6.5.2 answers your question where it
indicates that 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 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
the operation of a sprinkler. Thus, the additional 5 gpm does apply to multiple
dwelling units. “The Automatic Sprinkler Systems for Residential Occupancies
Handbook” explains that for singlefamily dwellings, the probability exists for
a fire to occur at the same time that a domestic fixture is in use. However,
the probability of such a simultaneous use is fairly small and the probability
that people will evacuate while keeping the domestic fixture flowing is
relatively small, so NFPA 13D does not require any consideration for
simultaneous domestic flow in single-family dwellings. However, in two-family
dwellings, the probability for larger simultaneous use during a fire is higher
because more people are potentially in the two dwelling units. Also, the
probability that a person in one dwelling unit will continuously use the water
while a fire is in the other dwelling unit is also higher, at least early in
the fire scenario. In recognition of these higher probabilities, NFPA 13D
requires an extra 5 gpm flow be added to the sprinkler demand to account for
this potential simultaneous demand. The 5 gpm only needs to be added to the
portion of the system that supplies both dwelling units as clarified in Figure
A.6.3(d). Any local requirement to add the domestic demand to the calculations
for one dwelling unit should be documented as a locally adopted amendment. The
5 gpm demand should be added as a total amount regardless of the number of
dwelling units. Logic makes you question if this is correct as one could assume
that if more than two dwelling units are being supplied by the connection, then
you would add 5 gpm per dwelling unit served but, a literal interpretation is
an appropriate approach for this situation. Although NFPA 13D was developed for
up to two family dwellings (aka a duplex), the IRC expanded its application to
townhouses and says to apply NFPA 13D as-is. You do want to check on any local
amendments that may modify this requirement. The AFSA intends to submit a
public input for the next edition of NFPA 13D to expand on the domestic demand
requirements when the IRC allows NFPA 13D to be applied to more than two
dwelling units. NFPA 13 and 13R have us account for domestic demand differently
as they anticipate greater demands to be placed on the water supply at any one
given time due to the number of potential occupants that will be using water
simultaneously IE apartments or similar structures.
