11
Hydraulic Calculations
Attic sprinklers must be calculated in conformance with these
guidelines. In all cases, the design area shall include the most
hydraulic demanding sprinklers. More than one set of
calculations may be required to prove different situations.
1. Attics Protected Entirely with Back to Back Attic Sprinklers -
For wet systems, calculate the most demanding 5 sprinklers.
For dry systems, calculated the most demanding 7 sprinklers
(see Fig. 16).
2. Attics Protected Entirely with a Mixture of Back to Back and
HIP Attic Sprinklers - For wet systems, calculate the most
demanding 5 sprinklers. For dry systems, calculate the most
demanding 9 sprinklers with a maximum of 7 to be back to
back sprinklers (see Fig. 17).
3. Attics Protected with Single Directional Attic Sprinklers - For
wet systems, calculate the most demanding 5 sprinklers. For
dry systems, calculate the most demanding 9 single directional
attic sprinklers or standard sprinkers, whichever is more
demanding (see Fig. 18).
4. Attics Having HIP Roofs with the HIP Joists Parallel to Outside
Wall - The design area requirements of NFPA 13 shall apply to
all sprinkler types (see Fig. 11).
5. Attics having a Width Greater than 60 ft., but in no Case
Greater than 80 ft. - For attics having HIP roofs with joists
parallel to outside wall, the requirements in Item 4 above
apply. For other attics, the requirements in Items 1 or 2 above
shall be used plus two additional standard type sprinklers
installed along the eave included in the calculation (see Fig.
19).
Example: Calculate the 9 most demanding single
directional attic sprinklers.
Figure 18
Single Directional Example
(Dry System Shown)
Wall
Wall
Example: When mixing back to back and standard
sprinklers at the eave, calculate the 7 most demanding
back to back sprinklers for dry systems or 5 most de-
manding for wet systems, plus the most demanding 2
additional standard sprinklers at the eave.
Figure 19
Attics Greater Than 60 Ft.
(Dry System Shown)
Figure 16
Back to Back Calculation Example
(Dry System Shown)
Example: Calculate the 7 most demanding back to
back sprinklers along the ridge.
Ridge
Figure 17
Mixed Attic Sprinkler Example
(Dry System Shown)
OBSOLETE
