Fire protection designs for concealed attic spaces present unique challenges that require tailored fire sprinkler solutions for effectiveness. The National Fire Protection Association (NFPA) sets industry standards for sprinkler system installation in NFPA 13.
However, it is crucial to consider site-specific needs for system selection when it comes to larger attics exceeding 40 feet in width.
As per research, sprinkler systems reduce fire damage by up to 97 percent. To address the complexities of protecting attics, two specially listed systems have been developed and adopted:
- Back-to-Back systems
- Low-Flow systems
These specialized solutions offer improved fire protection while reducing overall system costs. The choice between the two depends on the specific project requirements and the advantages each offers.
Both Back-to-Back and Low-Flow sprinkler systems employ similar strategies to combat fires efficiently. Firstly, sprinklers are strategically placed along ridge and hip lines to activate in response to rising heat quickly. Secondly, the sprinklers are closely spaced perpendicular to the roof’s slope.
Fire Protection Designs – Key Factors to Select Attic System
The selection of an appropriate specially listed attic system can be narrowed down to four key factors: roof slope, water supply, roof width, and site-specific needs.
Roof slope
Determining if the system is listed for the desired application is essential. Back-to-Back systems are unsuitable for slopes below 4:12, while Low-Flow systems are not recommended for slopes exceeding 6:12.
Water supply
Will the system work hydraulically with the available water supply? Low-Flow systems have the lowest hydraulic demand in attic applications, making them a viable option when the water supply is limited. However, the attic layout should still be considered.
Roof width
The width of the roof determines the number of branch lines required in the attic system, the necessary starting flow for Back-to-Back attic sprinklers, and whether specially listed attic systems are permitted in that space.
It’s important to note that roof width refers to the span or width of the attic for design purposes, typically measured at the intersection of the bottom and top chords of the roof truss at the eaves, excluding the roof overhang.
Insulation may also impact the effective roof width, making the protected attic space narrower than the total.
Site-specific needs
When dealing with attics wider than 40 feet, considering the site-specific needs is crucial for system selection. The difference in starting pressure and flow between Back-to-Back and Low-Flow sprinklers increases in these cases. This may require changes to pipe size, influencing the system choice.
Larger Low-Flow systems can often be designed with 2 1/2- or 3-inch main and feed piping, while larger Back-to-Back systems typically require 4-inch piping. The decision depends on cost-effectiveness, considering material and labor costs specific to each project.
Conclusion
In summary, the fire sprinkler industry has faced challenges in adequately protecting combustible concealed attics. However, developing Back-to-Back and Low-Flow sprinkler system designs offers effective and efficient options, surpassing the limitations of NFPA 13 prescriptive-designed systems. The choice between these systems ultimately depends on the unique configurations of the attic in question.
