Truss Force Calculator
Every truss transfers its share of the roof's total load down through its two end reactions into the bearing walls below. This calculator combines dead, live, snow, and wind load with your span and spacing to estimate the reaction force at each truss support.
Calculate Your Truss Support Force
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Live Roof Diagram
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How Load Becomes Force at Each Support
A truss engineer analyzes internal member forces using the method of joints — starting at a support or a joint with only two unknown forces, then working across the truss solving each joint's force balance in sequence. The total downward load on a truss ultimately splits into two upward reaction forces, one at each bearing wall.
For a simply supported symmetric truss under uniform load, each end reaction carries roughly half the truss's total tributary load (its span times its spacing times the combined dead, live, snow, and wind load per square foot). Asymmetric loading, cantilevers, or hip/valley girder trusses shift this balance and require full engineering analysis.
This calculator gives an estimated per-truss reaction force for planning wall and foundation bearing capacity — it is not a substitute for a full method-of-joints or finite-element analysis, which every stamped truss engineering drawing includes for each individual member.
Frequently Asked Questions
What is the method of joints in truss analysis?
The method of joints is a structural engineering technique that finds the force in every truss member by analyzing static equilibrium (sum of forces = zero) at each joint in sequence, starting from a joint with only two unknown member forces.
How much load does each truss support carry?
For a symmetric truss under uniform load, each of the two end supports carries roughly half the truss's total tributary load — its span times spacing times the combined roof load per square foot.