How this calculator works
Divide the distance between first and last truss positions by maximum spacing and round up to whole bays. Add one truss for the opposite end. Equal actual spacing divides roof length by that bay count. This avoids an oversized final bay when the length is not a spacing multiple. Geometry mode gives an ideal triangular top-chord slope only. Truss web layout, member sizes, bracing and connections must come from the truss designer.
Formula
bays = ceil(roof length/maximum spacing); trusses = bays + 1; actual spacing = roof length/bays; purchase = trusses x unit price; installation = crew hourly rate x total hours.
Worked example
A 10 m roof at 0.5 m maximum spacing has 20 bays and 21 trusses. At $100 each plus two crew hours at $50/hour, the estimate is $2200. At 3 m maximum spacing it needs four bays and five trusses.
Advertisement
Frequently asked questions
Why add one to the bay count?
Each bay lies between two trusses. A line of twenty bays therefore has twenty-one boundary trusses.
Does this choose safe truss spacing?
No. Enter spacing from the approved structural design and roof assembly requirements.
Are top-chord lengths fabrication dimensions?
No. Heel height, overhangs, joints, lumber thickness and engineered details change actual component lengths.