Calculator
Example Data Table
| Case | Span | Spacing | Pitch | Depth | Dead | Live | Snow |
|---|---|---|---|---|---|---|---|
| Light roof | 32 ft | 2 ft | 4:12 | 24 in | 10 psf | 20 psf | 15 psf |
| Snow region | 40 ft | 2 ft | 6:12 | 30 in | 12 psf | 20 psf | 35 psf |
| Wider spacing | 44 ft | 4 ft | 5:12 | 36 in | 14 psf | 20 psf | 25 psf |
Formula Used
The calculator uses a simplified simply supported truss analogy.
Service line load: w = (D + L + S + C) × spacing
Factored line load: wu = γD(D + C) + max(γL × L, γS × S), then multiply by spacing
End reaction: R = wu × L / 2
Maximum moment: M = wu × L² / 8
Chord force: F = M / d
Equivalent chord inertia: Ieq = (At + Ab) × d² / 4
Deflection: Δ = 5wL⁴ / 384EIeq
Deflection limit: Δallow = L / selected denominator
How to Use This Calculator
Choose the unit system first. Enter the clear horizontal span. Add the truss spacing and roof pitch. Enter overhangs if they apply. Add the vertical depth between chords.
Next, enter top and bottom chord areas. Add allowable compression and tension stresses. Use values from your code, supplier, or engineer. Enter realistic dead, live, snow, ceiling, and wind uplift loads.
Press Calculate to review geometry, loads, reactions, chord forces, stress ratios, and deflection. Use CSV or PDF export for project notes.
Article
About Vaulted Parallel Chord Truss Spans
A vaulted parallel chord truss carries roof loads across a clear span. It keeps the top and bottom chords nearly parallel. The whole truss follows a sloped roof profile. This shape gives a raised ceiling without a ridge beam.
Why Early Span Checks Matter
Early span checks help during concept design. They show if the chosen depth is reasonable. They also show how spacing and load choices change chord force. A deeper truss usually lowers chord force.
Method Used
This calculator uses a simplified beam analogy. The roof load becomes a uniform line load on one truss. The maximum bending moment is converted into chord force. The vertical truss depth acts like the lever arm. Service load is used for deflection. Factored load is used for strength checks.
Important Design Notes
Vaulted trusses need careful attention. The slope changes member lengths and roof geometry. Bearing points must resist vertical reaction and possible uplift. Web layout must provide stable load paths. The panel count estimate helps judge web spacing.
Deflection and Limits
The deflection estimate is also simplified. It uses an equivalent chord inertia. Real truss deflection depends on joint stiffness. It also depends on web strains and connection slip. Use the result as a planning guide. Final sizing should come from a licensed engineer.
Input Quality
Good inputs make the result more useful. Use realistic dead, live, snow, and ceiling loads. Enter local wind uplift if it applies. Use material values from your code, supplier, or engineer. Keep the same unit system for all fields.
Interpreting Results
A passing result does not approve construction. It only suggests the chosen span, depth, area, and loads are within the simple checks. Failed results are still useful. They show whether more depth, closer spacing, stronger chords, or lower loads may help.
Practical Workflow
For best use, compare several options early. Try different truss depths. Review uplift reactions. Share it with the design team before detailed drawings begin.
Final Reminder
Remember that local codes may control load combinations. Snow drift, attic equipment, ceiling finishes, and solar panels can change demand. Connections may govern before chords do. Always verify bearing, bracing, and transport limits before ordering materials on site.
FAQs
What is a vaulted parallel chord truss?
It is a roof truss with top and bottom chords that stay nearly parallel. The truss follows a sloped roof shape and creates a vaulted interior ceiling.
Is this calculator a final structural design?
No. It gives simplified preliminary checks only. Final truss design must include code loads, member design, web design, connections, bracing, bearings, and engineering review.
Why does truss depth matter?
Depth works like a lever arm between chords. More depth usually lowers chord force and deflection. Shallow trusses often need stronger chords or closer spacing.
Which roof loads should I enter?
Enter dead load, live load, snow load, ceiling load, and wind uplift when applicable. Use local code values or project values from a qualified designer.
How is chord force estimated?
The calculator finds maximum simple-span moment. It then divides that moment by the vertical truss depth. This gives an approximate chord axial force.
What deflection limit should I use?
Common service limits include L/240, L/360, and L/480. The correct limit depends on roof finishes, ceiling finishes, codes, and owner requirements.
Can I use metric units?
Yes. Select Metric before entering values. Use meters for span and spacing, millimeters for depth, kPa for loads, MPa for stress, and mm² for areas.
Why is uplift shown separately?
Wind can create net upward reaction after dead load is deducted. Uplift may require hold-downs, clips, straps, or special bearing details.