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 sprinklers, whichever is more demanding (see
Fig. 18).
4. Attics Having HIP Roofs with the HIP Joists Parallel to
Outside Wall (see Fig. 11) or attics having a mixture of
standard spray sprinklers and Specific Application Attic
Sprinklers
TM
- The design area requirements of NFPA 13
shall apply to all sprinkler types.
5. Attics having a Width Greater than 60 ft.
(18.3m)
, but in
no Case Greater than 80 ft.
(24.4m)
- 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
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7
8 9
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
demanding 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
1 2 3 4 5 6 7
Figure 17
Mixed Attic Sprinkler Example
(Dry System Shown)
3 4 5 6 7 8 9
1
2
OBSOLETE
