Fire sprinkler systems may be used as an effective method of providing fire protection, as well as being highly compatible with Metal Plate Connected Wood Truss (MPCWT) systems. When fire sprinkler systems are used with truss systems, it is essential to design the trusses to carry the additional dead load and required live loads imposed by the fire sprinkler system, as well as to comply with standards. for fire protection. This guide covers basic information that should be considered by the Building Designer and Truss Designer in designing the truss system for use with a sprinkler system. 

For additional information regarding sprinkler systems applicable to the following, please see:

Step-by-Step

Intro

Introduction

  • 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.

Step 1

Dead Loads

  • 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

Step 2

Live Loads

  • 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


Step 3

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

Step 4

Special Engineering

  • 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.