Frequently Asked Questions
How many trusses for a 40-foot building at 24 OC?
ceil(40 / (24/12)) + 1 = ceil(20) + 1 = 21 trusses.
How long is the top chord for a 28-foot wide building at 6:12 pitch?
Top chord per side = (28/2) / cos(atan(6/12)) + 1 = 14 / cos(26.6 deg) + 1 = 14 / 0.8944 + 1 = 15.65 + 1 = 16.65 ft.
What is the standard roof truss spacing?
24 inches on center is the standard for engineered roof trusses. Some designs use 16 OC for heavy snow loads or special sheathing requirements. Trusses are engineered as complete structural systems and can be spaced at 24 OC because the truss depth provides enough stiffness; conventional rafter framing typically uses 16 OC because individual 2x lumber at 24 OC would be undersized for most spans.
Should I buy trusses or frame with rafters?
Trusses are faster to erect, use less lumber overall, and are structurally engineered. Conventional rafters allow attic access and are preferred when the attic will be finished living space.
What overhang should I use?
This calculator adds 1 ft of overhang to each chord for a total 2-ft overhang. Standard residential overhangs range from 12 to 24 inches. Adjust with your fabricator for your specific design.
Do I order one truss per position or per pair?
One truss per position. A gable roof 40 ft long at 24 OC needs ceil(40/2) + 1 = 21 trusses, not 21 pairs. Each truss is the full width of the building.
What does the lumber estimate include?
This calculator shows top and bottom chord linear footage only. Web members, metal connector plates, gable-end framing, and ridge blocking are not included. Expect the fabricated truss to cost more than raw lumber cost would imply.
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Estimates for informational purposes only.
Important Disclaimer: Estimates for informational purposes only.
This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.