Calculator Inputs
Use consistent metric units. Loads are treated as downward area loads and converted to a uniform line load on the truss projection.
Formula Used
Pitch angle = atan(rise ÷ span)
Pitch per 12 = (rise ÷ span) × 12
Slope factor = √[1 + (rise ÷ span)²]
Support slope length = √(span² + rise²)
Full top chord length = (span + left overhang + right overhang) × slope factor
Roof area per truss = full top chord length × spacing
Service line load = (dead + live + wind) × spacing × slope factor
Total load = service line load × total horizontal projection
Uniform-load reactions: RB = W(x̄ − a) ÷ span, RA = W − RB
This page uses a simplified, uniformly loaded mono roof truss model for layout, load planning, reactions, and basic moment trends. It does not replace full structural design, code checks, connection design, or member-by-member engineering verification.
How to Use This Calculator
- Enter the clear span between the two support points.
- Type the vertical rise for the mono slope.
- Add left and right overhang lengths if your roof extends beyond supports.
- Enter truss spacing to define tributary roof width.
- Input dead, live, and wind loads using the same unit system.
- Set the load factor to 1.00 for service values or increase it for comparison.
- Press Calculate Truss to display results above the form.
- Review the graphs, then export your report as CSV or PDF.
Example Data Table
| Case | Span (m) | Rise (m) | Overhangs (m) | Spacing (m) | Total Load Intensity (kN/m²) | Top Chord Length (m) | Total Load (kN) |
|---|---|---|---|---|---|---|---|
| Small Shed Roof | 6.00 | 1.20 | 0.30 / 0.30 | 1.00 | 1.35 | 6.73 | 9.09 |
| Workshop Roof | 8.00 | 1.60 | 0.45 / 0.60 | 1.20 | 1.65 | 9.23 | 18.27 |
| Light Industrial Bay | 10.00 | 2.00 | 0.50 / 0.80 | 1.50 | 1.90 | 11.52 | 32.84 |
Important Design Note
Use this calculator for conceptual sizing, comparison, and communication. Final design should consider local codes, member forces, deflection limits, uplift, bracing, fasteners, support conditions, purlin layout, material grade, snow or seismic effects, and engineer-reviewed load combinations.
FAQs
1) What does this mono roof truss calculator estimate?
It estimates mono roof geometry, roof area per truss, service and factored loads, support reactions, pitch, and a simple bending moment trend. It is useful for planning and comparison before detailed structural design begins.
2) Is this tool enough for final engineering design?
No. It simplifies the truss as a uniformly loaded structural line. Final design still needs member sizing, connection design, code combinations, uplift checks, deflection review, and approval by a qualified structural professional.
3) Which units should I use?
Use one consistent unit system throughout the page. The sample setup assumes meters and kN/m². If you switch units, keep every dimension and every load value compatible to avoid misleading results.
4) Why are dead, live, and wind loads entered separately?
Separate inputs make it easier to understand how each load source contributes to the total. They also improve comparison between roofing options, spacing changes, and early-stage load assumptions during layout decisions.
5) Do overhangs affect support reactions?
Yes. Overhangs shift the load centroid relative to the supports. Unequal overhangs can increase one reaction and reduce the other, so they should be included whenever the roof projects beyond the bearing points.
6) What does the load factor change?
The load factor scales service loads to create a comparison-level factored load set. It helps you see how reactions and moments change under higher design assumptions without changing the base geometry inputs.
7) Can I enter wind uplift as a negative value?
This version expects downward equivalent wind input. Uplift, load reversals, hold-down requirements, and net pressure combinations should be reviewed separately because they can change reactions, connection demands, and stability checks.
8) Can I export the calculation results?
Yes. After calculation, use the CSV button for spreadsheet-friendly data or the PDF button for a clean summary report. Both export the input values and the calculated output set.