Your state may be the next to mandate these systems, so
it’s a good idea to understand how they work
A small but growing number of code jurisdictions now require
fire sprinklers in new and substantially remodeled homes. That
number is bound to increase as states adopt the 2009 IRC, which
requires sprinklers in all new one- and two-family residences
and townhouses. Not all states, of course, will choose to
implement the new rule — but in ones that do, builders
will need to get up to speed on these systems.
The company I work for designs and inspects residential and
commercial fire sprinklers. In this article I’ll focus
primarily on residential sprinkler systems — how they
work and what builders need to know about their
Residential vs. Commercial
Fire-sprinkler systems must comply with standards published by
the National Fire Protection Agency (NFPA). Sprinklers for one-
and two-family dwellings are covered by NFPA 13D, which is the
basis for the sprinkler requirements in the 2009 IRC.
Residential systems don’t serve quite the same purpose
as commercial systems. The sprinklers used in commercial
buildings are designed to protect both life and property, and
they’re sized to supply water to many heads for at least
30 minutes. Residential sprinklers, by contrast, have a single
overarching goal: to protect the lives of the home’s
occupants. Property protection is a secondary concern. Systems
in one- and two-family dwellings are sized to supply at least
two heads for a minimum of 10 minutes. This should hold the
fire at bay long enough for the occupants to escape and the
fire department to arrive on the scene.
Types of Systems
Residential fire sprinklers can be designed as stand-alone or
multipurpose systems (see Figure 1).
Figure 1. There are two basic types of sprinkler
systems: stand-alone and multipurpose. In a stand-alone system,
water enters the sprinkler pipes and remains there until a head
activates or the system is drained for maintenance. Because
this noncirculating water can become stagnant, a check valve is
required to prevent it from contaminating the potable water.
In a looped multipurpose system, the heads are arranged
along a continuous circuit. The plumbing fixtures draw their
supply water through sprinkler heads, so there are no dead ends
where water can stagnate.In a networked multipurpose
system, sprinkler heads and fixtures are connected by a web of
1/2-inch PEX lines. Though small in diameter, these lines can
provide the necessary flow because there are multiple
connections between the heads and the plumbing
Stand-alone. In a stand-alone system, the sprinklers
are piped separately from the potable water supply and are
isolated from it by a check valve. The check valve is necessary
because the water in the sprinkler piping does not circulate
and may become stagnant.
Multipurpose. In a multipurpose system, the sprinkler
piping is part of the cold-water plumbing supply. Stagnation
isn’t a problem because fresh water enters the sprinkler
lines every time a plumbing fixture draws water.
Multipurpose systems are generally piped in either looped or
networked configurations. In a looped system, heads are
installed along or just off a line that runs in a loop around
the house. To prevent stagnation, the designer avoids the long
dead-end runs often found in stand-alone systems.
Networked multipurpose systems can only be made with PEX
(cross-linked polyethylene) piping. Each head is fed by four
connections. A web of 1/2-inch PEX lines connects the heads to
each other, to the supply manifold, and to fixtures.
Licensing. In many jurisdictions, plumbers can
install multipurpose systems without special licensing.
Stand-alone sprinkler systems, however, typically require a
Contrary to what you see in the movies, sprinkler heads do not
all go off at once. Although such systems exist, they’re
used only in high-hazard areas like power plants and
The heads in residential (and most commercial) systems are
individually activated by heat in the surrounding air. A
typical residential sprinkler has a glass bulb containing a
fluid that expands when exposed to heat. When the rated
temperature is reached — usually between 155°F
and 175°F — the glass shatters and water
begins to flow (Figure 2). Other residential
heads rely on a fusible link — pieces of metal soldered
together. When the rated temperature is reached, the solder
melts, the link comes apart, and the sprinkler comes on.
Figure 2. Heads automatically activate when the air
surrounding them reaches a predetermined temperature —
typically between 155°F and 175°F. The
glass bulb in the sprinkler at left contains a liquid that
expands when heated. At the critical temperature, the pressure
breaks the bulb and releases the water. The head at left relies
on a fusible link of soldered metal that melts at the critical
temperature, activating the flow. Photos: Viking
Spray pattern. Fires in dwellings usually start at
the perimeter of the room — where the furniture and
drapes are — so residential sprinklers spray in a pattern
that hits high on the walls. Commercial heads spray down, in a
conical pattern, because the fuel is assumed to be more evenly
distributed throughout the building.
Response time. Residential sprinklers begin to
operate 30 to 60 seconds after the critical temperature is
reached. The goal is to catch the fire before it has time to
activate more than two heads. If more than two are activated,
there may not be enough water pressure to achieve the desired
There are two main types of residential heads: pendants and
sidewall sprinklers. Pendants spray down from the ceiling and
sidewall heads spray out from the wall. Pendants are more
common; sidewall sprinklers are used when there is no clear
path to run pipes to pendants. Sidewall heads can also be used
in retrofit situations to avoid cutting and patching the
ceiling (Figure 3).
Figure 3. Pendants are the most common type of head;
they are either left exposed (A) or concealed behind flat (B)
or domed (C) cover plates. The plates are heat-sensitive and
designed to fall off at a slightly lower temperature than is
necessary to activate the head. Sidewall sprinklers (D) are
typically left exposed, though some can be hidden by
dome-shaped covers. Photos:Tyco Fire &
Pendants are frequently concealed behind flat or dome-shaped
cover plates, which are soldered to an escutcheon threaded into
the sprinkler assembly. At a predetermined temperature the
solder melts, a spring ejects the cover, and a deflector pops
down. The head activates shortly thereafter, and the water hits
the deflector and fans out in the desired spray pattern.
Cover plates must not be painted: Paint alters a plate’s
heat sensitivity and may prevent it from releasing at the
Coverage. The number of sprinklers needed is based on
the size of each room; in residential systems the goal is to
spray at least 0.05 gallons of water per minute per square foot
of floor area. Coverage per head ranges from a low of 12 feet
by 12 feet to a high of 20 feet by 20 feet. Some residential
heads will work with as little as 13 gallons per minute (gpm),
while others use up to 26 gpm. Commercial sprinklers, not
surprisingly, require much more water.
Placement. As a rule, sprinklers must be at least 8
feet apart. If they’re closer together than that, the
first one to go off may cool the area enough to prevent its
neighbor from activating.
Sprinkler heads must be located away from any heat sources
that might accidentally set them off — a minimum of 60
inches (measured horizontally) from the front of a fireplace,
18 inches from a kitchen stove, and 6 inches from a water
heater or furnace. Beams, lights, and ceiling fans can cause
problems, too, by blocking a sprinkler’s spray or
interfering with its response time. The NFPA standards —
as well as manufacturers’ installation guidelines —
include specific rules for placing heads to avoid
Required areas. The vast majority of fatal fires in
homes begin in the living room, family room, bedroom, or
kitchen. NFPA 13D requires fire sprinklers in all of these
rooms, as well as in any other space not specifically exempted
by the standard (Figure 4).
Figure 4. Under NFPA 13D — the basis
for the 2009 IRC sprinkler requirements — sprinkler heads
are required in the main living areas of a home, though not in
small baths and closets. Garages, crawlspaces, and attics are
also exempt unless they contain a fuel-burning appliance. Local
codes may vary, however.
For example, bathrooms smaller than 55 square feet and closets
smaller than 24 square feet and less than 3 feet deep do not
need sprinklers. Nor do unheated entry areas, garages, or
attics and crawlspaces that do not contain fuel-burning
appliances. Keep in mind, though, that local jurisdictions may
have different requirements; many require garages to have
sprinklers, for instance.
The pipes in residential sprinkler systems can be made of
steel, copper, or certain plastics. Most are made from CPVC
(chlorinated polyvinyl chloride) or PEX. CPVC piping can be
installed in stand-alone and multipurpose piping systems
(Figure 5). At present, PEX piping can be used
only in multipurpose systems (see “Using PEX for Fire
Sprinklers,” below). Metal piping can be left exposed,
but plastic pipes and fittings generally need to be covered by
a thermal barrier like drywall.
Figure 5. CPVC pipe flexes enough to be pulled into
joist bays (top left), where it can be glued and then inserted
into fittings (top right). The system above has been tested for
leaks and is ready for drywall to be installed. The head is
covered by a protective plastic cap, which will be removed
after painting and replaced with a trim piece or cover
Storage. CPVC and PEX pipes should always be tarped
when stored outdoors, because direct sunlight weakens them and
makes them less flexible. If a building inspector sees fading
in CPVC sprinkler pipe — indicating that it’s been
exposed to sunlight — he’ll fail the system.
Size. How big the piping needs to be depends on the
hydraulic demand — the pressure and flow required to
operate that particular system. Low water pressure can be
offset by using larger pipe, reducing the number of fittings,
or spacing heads so that no one sprinkler uses more than 13
If 60-psi water is available at the street, a stand-alone
system in a one-story 2,500-square-foot home can usually be
made with one-inch pipe.
Risers. In a stand-alone system, the sprinklers and
overhead piping are supplied through a riser (Figure
6). The riser contains a check valve and a drain
valve, which is used to empty the system for repairs and to
verify that there’s water inside. Many risers also have a
pressure gauge, though it’s not required.
Figure 6. The pipes in a stand-alone system are
supplied through a riser, which contains a check valve to
prevent sprinkler water from entering the potable water supply
(illustration, top). By code, sprinklers may not have a
separate shutoff valve. Here, an installer tightens the check
valve on a riser (bottom left); a plumber will later connect
the main water supply to this valve. The CPVC pipe on the left
is a drain line that terminates outside the house (bottom
Most stand-alone systems are equipped with a flow detector, an
electric device that sets off an audible alarm when water flows
into the sprinkler pipes. Flow detectors aren’t required
if the house has smoke detectors, but they’re typically
included as part of the sprinkler system anyway.
A stand-alone system’s main control valve must be
upstream from the connection to the domestic water so that the
sprinklers can’t be shut off without the domestic water
being shut off as well. (Exceptions are when the control valve
can be locked open or when it’s monitored by a central
alarm station.) This safeguard makes it less likely that anyone
will leave the sprinklers off.
Problems with freezing. In cold climates it’s
important to make sure that the sprinkler pipes in upper-floor
ceilings won’t freeze and break. This can be done either
by keeping pipes inside the home’s thermal boundary or,
in stand-alone systems, by filling them with a mixture of
glycerin and water — an anti-freeze solution approved for
use in CPVC. A reduced-pressure backflow-prevention valve (a
type of double check valve) may be required to ensure that the
mixture does not get into the potable water.
Altogether, it takes several weeks to design the system, get
through plan review, and obtain a permit, so it’s best to
bring the sprinkler designer or installing contractor on board
at the beginning of the project. Waiting until well into
construction is a common and costly mistake.
Water service. Many contractors fail to consider the
water supply. The underground piping and the water meter must
be large enough to provide the necessary flow. A residential
system typically requires a 1-inch meter — a 5/8- or
3/4-inch meter probably isn’t adequate. The only way to
know for sure what size meter is needed is to design the system
and then calculate its hydraulic demand.
A well works fine with fire sprinklers as long as it can
produce the required flow for 10 minutes straight —
usually about 300 gallons. If the flow is insufficient, a
standby water source will be needed, such as a pressurized or
elevated storage tank.
Completing the Job
Once the piping is in place, the heads are installed and the
system is tested for leaks. All piping must remain visible
until the system has been inspected by the building official.
The heads come with temporary plastic covers to protect them
while the drywall is hung and painted. When the painting is
complete, the sprinkler installer removes the temporary caps
and replaces them with the finish trim.
Dan Thacker is the design manager for
Engineered Fire Systems in Grass Valley, Calif.