Feature Articles
Potential Pitfalls of Unsprinklered (and Sprinklered) Attics
by Russell P. Fleming, P.E.
October 1, 2009
The list is extensive, but several of them can be addressed by meeting the requirements of applicable codes and standards.
When automatic fire sprinkler systems are installed in a building, the attic area deserves special attention. Sometimes fire sprinklers are installed in the attic, sometimes not.
When Are Attics Sprinklered?
Individuals
that deal mainly with residential construction may get the impression that
attics are never sprinklered, but the allowance to omit sprinklers from
combustible attic spaces is a fairly recent development, one that accompanied
the 1980s’ development of special sprinkler installation standards aimed at encouraging
low-cost protection for dwellings and multiple dwellings. As shown in Table 1, NFPA (National Fire
Protection Association) standards 13D and 13R both allow omission of sprinklers
from attics not used or intended for living purposes (or storage in the case of
NFPA 13R) and that do not contain fuel-fired equipment.
The rules are different for traditional sprinkler systems installed in
accordance with NFPA 13, Installation
of Sprinkler Systems. Under the provisions of that standard,
sprinklers are required in all combustible attic spaces. Even when the attic is
constructed of noncombustible and limited combustible construction, sprinklers
can only be omitted if the space has no access or only limited access, such
that it cannot be used for occupancy or storage.
If the space has no access or only limited access such that it cannot be used
for occupancy or storage, but is enclosed wholly or partly by exposed
combustible construction, it is required to be sprinklered, unless it falls
under one of the 14 subsections now labeled as 8.15.1.2.3 through 8.15.1.2.16.
The minimum clear space below which it is considered impractical to provide
sprinkler protection is a depth of six inches, as demonstrated by the wording
of subsections 8.15.2.3, 8.15.2.4, and 8.15.2.5. Section 8.15.1.5 allows the
use of partial protection where combustibles are localized, and the two
subsequent sections spell out special rules for sprinkler protection of flat
shallow combustible concealed spaces.
Sprinklers in Attics Based on Draftstopping
Improper insulation for sprinkler piping in unheated attic - piping should be below batt insulation, not wrapped and insulated from building heat. All photos by Russell Fleming.
For occupancy Groups R-1 and R-2 (hotels, motels, apartments, dormitories, etc.) the draftstopping is required above and in line with sleeping unit and dwelling unit separation walls, while for other occupancies the draftstopping is required so as to create areas not greater than 3,000 square feet. Group R-2 occupancies not exceeding four stories in height must have combustible attic draftstopping every 3,000 square feet or above every two units, whichever area is smaller.
Exceptions are provided to state that the draftstopping is not required in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1, which references the installation of an NFPA 13 sprinkler system. Because of past confusion, a separate section now states that draftstopping is also waived for Group R-1 and R-2 occupancies protected with an NFPA 13R sprinkler system in accordance with Section 903.3.1.2, “provided that automatic sprinklers are also installed in the combustible concealed space.”
So, even where NFPA 13R would allow the omission of attic sprinklers, sprinklers might be provided to eliminate the need for attic draftstopping. In past years, confusion in this area often led to change orders, adding attic sprinklers to NFPA 13R systems.
A List of Potential Problems
Unsprinklered Attics
Wrapping sprinkler pipes with insulation in an unheated attic space provides almost no protection against freezing.
NFPA 13, however, which has an emphasis on the protection of property as well as life, addresses the potential for a fire originating in an attic space or traveling to an attic space from an exterior point of origin. Attic fires have been known to originate with lightning strikes or to result from fire spread up the side of a building from dumpsters, mulch and similar external sources.
Combustible Trusses. The increased use of lightweight combustible trusses in attics is generally acknowledged to increase the fire hazard of the unsprinklered attic, due to the expected earlier failure of these assemblies in a fire event compared to traditional solid joist construction. While the attic fire presents a challenge to sprinklers, rules within NFPA 13 have been tightened in recent years to help ensure that sprinklers are able to promptly contain and control such fires.
A List of Potential Problems
Sprinklered Attics
The two main issues with sprinklered attics are:
Freezing Temperatures.
Special precautions must be taken to protect pipes from freezing and, thereby,
prevent system damage.
Too Little Water for Designed
Areas. Special care is needed with water supply requirements to
control system installation costs. The
design area for the sprinkler system dictates the needed water supply and is
based on a reasonably conservative estimate of the maximum number of sprinklers
likely to operate during a fire event. Certain characteristics of attics tend
to increase the needed water supply, such that the attic demand can easily
exceed the demand of the rest of the building.
A slope of more than two in 12 (16%) tends to skew the operating pattern of
sprinklers, and the design area is therefore increased by 30% to accommodate
such a roof pitch. Another 30% design area increase is required by NFPA 13 when
the attic system is a dry pipe system, often needed to accommodate freezing
temperatures.
One way in which the NFPA Sprinkler Committee has attempted recently to keep
the water supply demand for the attic area reasonable, is by allowing the use
of small orifice (K-4.2) sprinklers in dry pipe systems where the piping is
corrosion resistant or internally galvanized. This helps hold down the flow
needed for individual sprinklers. Special listed attic sprinklers are also
available with extended coverage protection areas, which can often reduce the
overall number of attic sprinklers and the design flow.
Wet Pipe Systems
Improper Insulation.
Where wet pipe system piping extends into an unheated attic to serve
sprinklers in the heated floor area below, it is important that the piping be
properly insulated. As shown in annex diagrams in both NFPA 13D and NFPA 13R,
the insulation blanket should be placed on the unheated attic side of the
piping, with no insulation between the piping and the ceiling of the heated
area below. All too often, insulators accustomed to dealing with plumbing and
heating systems wrap the sprinkler piping in insulation, insulating it from the
warm building envelope as well as the attic cold.
With no flow through the sprinkler piping under normal conditions, insulating
the piping in this manner can lead to freezing and subsequent water discharge
from ruptured piping. For similar reasons, caution must be taken with blown-in
insulation so that the insulation does not settle into the space between the
wet sprinkler piping and the heated space. Ideally, fiberglass batt insulation
can be “tented” over the top of the sprinkler piping prior to the application
of the blown-in insulation.
Caution must also be exercised when considering the use of spray foam
insulation in conjunction with nonmetallic sprinkler piping. Chemical
compatibility must be ensured in advance with the piping manufacturer to avoid
the possibility of environmental stress cracking of the plastic pipe.
Dry Pipe Systems
While hanging lengths may have been properly established at the time of installation (left), settling of wood trusses may create improper pitch of dry system piping in sprinklered attics.
For trapped sections of piping, drum drip drains, which employ two shutoff valves separated by a short length of piping, can ideally be situated in areas in which heat is provided so as to allow periodic draining of collected moisture. The upper valve is normally maintained in the open position, closed when the drum is drained so that system air pressure is not lost, and then re-opened when the lower valve is again closed.
In attics of wood truss construction, it is worthwhile to check the pitch of piping prior to the onset of freezing weather for the first year or two. The trusses often settle in place once the roof is fully loaded, and hangers placed on piping during initial construction may need to be adjusted to maintain proper pitch. Low points that are inadvertently created have the potential to freeze and rupture if water accumulates.
Following a trip during freezing weather, special precautions should be taken to ensure that ice is not left in a dry system when it is drained. Such ice can thaw and result in water accumulations that exceed the capabilities of low-point drains.
Current Issues
A company that manufactures a coated application of fire retardant appealed to the NFPA Standards Council to delete the new section, claiming that it would infringe on the ability of the local authority having jurisdiction to determine if their product is equivalent to fire-retardant treated wood. The Standards Council denied the appeal, meaning that the annex statement will be included in the 2010 edition of NFPA 13.
Twenty years after the publication of the first edition of NFPA 13R, controversy also continues to exist with the basic question of whether sprinklers should be omitted from attics in accordance with that standard. A March 2009 change to the Massachusetts Building Code requires the use of NFPA 13 systems in Group R occupancies with a total floor area exceeding 12,000 square feet, based mainly on a 2008 fire in an apartment complex that burned up the exterior of a building to reach an unprotected attic space. Overall, however, the record of NFPA 13R systems has been excellent, and the creation of that standard has been credited with saving countless lives and residential properties.
Protection of attics is a major difference between the various NFPA sprinkler installation standards, and an important cost factor in the provision of sprinkler systems for combustible construction. As such, these spaces deserve special attention with regard to the design, installation and maintenance of fire sprinkler systems.
Russell P. Fleming, P.E.
Russell P. Fleming, P.E.,
is the executive vice president of the National Fire Sprinkler Association. He
has more than 30 years of service on the NFPA 13 Sprinkler Committee, is a past
member of the NFPA Board of Directors, and past chairman of its Standards
Council. A Fellow of the Society of Fire Protection Engineers, he has served as
an adjunct in the fire protection engineering program at Worcester Polytechnic
Institute, writes a regular column on fire sprinkler issues for the NFPA Journal, and has authored chapters in NFPA and SFPE
technical handbooks. Contact him at fleming@nfsa.org.
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