- Building Designers must account for the dead and live loads of fire sprinkler systems in the building design.
- Truss Designers must incorporate these additional loads into the truss design.
- This step by step contains general guidance and industry best practices, and applies to both roof and floor trusses.
- Specific designs should be confirmed with the local building authorities.
- Trusses must be designed to carry the additional weight of the sprinkler system.
- Both the pipes and the water inside are considered a dead load.
- The fire sprinkler system can be supported from either the top chord or the bottom chord of the truss.
- The Building Designer should provide the following information to the Truss Designer:
- Uniform dead load to account for the sprinkler system
- Any concentrated dead loads not included in the uniform load, if applicable
- Where attachment locations are known, concentrated dead loads for the sprinkler system may be given instead of uniform loads
- Typical values range from 1.5 to 6 PSF, depending on the nominal size of the pipe and the hanger spacing.
- Consult the Building Designer or sprinkler system Engineer to obtain exact values
- The trusses should also be designed for a 250 lb concentrated live load
- This is applied to any single support point, but not simultaneously to all support points.
- The intent of the 250-lb. live load provision is to accommodate the weight of sprinkler installation personnel for a very short time during installation
- If multiple sprinkler lines are attached to the same truss, the 250 lb load should be applied at only one location at a time, representing only one worker per truss
- The 250-lb. live load need not be considered simultaneously with other live loads (i.e., roof, snow, wind, etc.).
- Most truss design software can automatically apply a specified “sprinkler load”to each panel and mid-panel point in separate load cases
- This approach is conservative, but allows for variance in the installed location
Truss Layout and Webbing
- Truss construction is highly compatible with sprinkler systems.
- The truss designs and sprinkler system design need to be coordinated to eliminate conflicts
- Ideally, sprinkler system water lines run through open webbing, and attachment points coincide with panel points.
- If coordinated in advance, panel lengths and webbing configurations can easily be modified to accommodate.
- Truss construction along with advance planning can safeguard the builder against issues such as:
- Drilling through structural members for pipe runs
- Loss of headroom due to piping
- Additional engineering design may be required if any of the following conditions are present:
- Large diameter (>4”) pipe lines
- Significant risers
- Pipe lines running parallel to trusses
- A maximum of one sprinkler system support may be attached to each truss panel.
- If more than one support is needed in any panel, special engineering is required, and a Registered Design Professional should be contracted.
- Lateral loads resulting from sprinkler systems, where required, should be evaluated separately by a Registered Design Professional.