American Fire Sprinkler Association
12750 Merit Drive, Suite 350 Dallas, TX 75251
Ph: (214) 349-5965 Fax: ((214) 276-0908
TECHNICAL UPDATE
MARCH 2, 2007
"I have a soffit that is over 30 inches wide. When referencing NFPA
13:8.6.5.1.2, I can locate my sprinkler head accordingly to comply
with (#1) subsection 8.5.5.2, table 8.6.5.1.2 and figure 8.6.5.1.2
(a). However I do not comply with (#3) obstructions located against
the wall and that are not over 30 inches in width shall be permitted
to be protected in accordance with figure 8.6.5.1 (b). Are sprinkler
heads required under the soffits over 30 inches wide to provide
adequate coverage below the soffits?"
We have reviewed the 2002 Edition NFPA 13 as the applicable Standard.
Our informal interpretation is that sprinklers will not be required
under soffitts that are over 30 inches in width if you comply with
the "Beam Rule" requirements of Figure 8.6.5.1.2 (a) and Table
8.6.5.1.2.
Confusion can exist between applying the requirements of obstruction
against walls (Soffit Rule) and the obstructions to sprinkler
discharge (Beam Rule). The Soffit Rule: Figure 8.6.5.1.2 (b) applies
to soffits up to and including 30-inches in width and can not be used
for soffits that are wider then that. A note on soffits that must be
addressed is that to qualify as a soffit; it must have a solid bottom
plate. You cannot apply the soffit application to a Valance, which
will not be enclosed at the bottom plane. The advantage that the
Soffit Rule over the Beam Rule is shown in Figure 1 is that the
Soffit Rule allows you to locate a sprinkler closer to the wall then
what would be allowed by the use of the Beam Rule. This is one of the
reasons why the Soffit Rule is not allowed to be applied to soffits
that exceed 30-inches in width.
As shown in Figure 1, we have a soffit that is 18-inches deep and 30-
inches wide. The deflector of the sprinkler in both the Soffit Rule
and Beam Rule applications is located 3-inches down from the ceiling.
The Soffit Rule (A≥ (D - 8 in.) + B) will allow the sprinkler to be
located 3 ft. 1 inch (30 - 8 + 15 (18 - 3) = 37 inches) from the
side of the soffit. Appling the Beam Rule to this same situation,
with the sprinkler deflector located 15-inches above the bottom of
the soffit, the closest that the sprinkler can be located to the side
of the soffit using Table 8.6.5.1.2 is 4-ft. 6-inches.
So as shown, the Soffit Rule will allow a sprinkler to be located
closer to the soffit then the Beam Rule. If the sprinkler cannot meet
either application, an additional sprinkler will have to be installed
beneath the soffit. When applying either rule, the area of coverage
of the sprinkler is determined by the distance of the sprinkler from
the wall and not from the side of the soffit.
-----------------
Technical Update is prepared by the Technical Services Dept. of the
AFSA: Vice President of Engineering and Technical Services Roland
Huggins, a PE registered in fire protection engineering; Phill Brown,
a NICET IV certified automatic sprinkler technician and NFPA
Certified Fire Protection Specialist (CFPS) and Tom Wellen, a degreed
fire protection engineering technologist. This is provided with the
understanding that the AFSA assumes no liability for this opinion or
actions taken on it and they are not to be considered the official
position of the NFPA or its technical committees.
Copyright (c) 2007, American Fire Sprinkler Association. All
Rights Reserved
--------------------------
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