Enter Roof Truss Data
Example Data Table
| Case | Span | Spacing | Pitch | Dead | Live | Snow | Wind uplift | Use case |
|---|---|---|---|---|---|---|---|---|
| Light roof | 24 ft | 24 in | 4:12 | 14 psf | 20 psf | 15 psf | 12 psf | Simple garage |
| Standard home | 30 ft | 24 in | 6:12 | 18 psf | 20 psf | 25 psf | 18 psf | Residential framing |
| Heavy finish | 36 ft | 19.2 in | 8:12 | 24 psf | 20 psf | 35 psf | 22 psf | Tile or dense ceiling |
| High uplift | 28 ft | 16 in | 5:12 | 16 psf | 20 psf | 10 psf | 32 psf | Coastal tie check |
Formula Used
Slope factor: √(rise² + run²) ÷ run
Loaded width: span + 2 × overhang
Plan area: loaded width × roof length
Roof surface area: plan area × slope factor
Dead load: [(top dead + cover) × slope factor] + bottom dead + truss self weight ÷ spacing
Service load: dead load with allowance + live load + snow load
Factored load: D factor × dead + L factor × live + S factor × snow
Line load: load psf × truss spacing in feet
Reaction: line load × loaded width ÷ 2
Net uplift: wind factor × wind uplift − stabilizing dead factor × dead load
Maximum moment: factored line load × span² ÷ 8
Estimated chord force: maximum moment ÷ estimated truss depth
These equations simplify truss behavior. They do not replace engineering, local code checks, or sealed truss shop drawings.
How to Use This Calculator
- Enter the clear span between bearing walls.
- Enter roof length and overhang to estimate roof area.
- Add truss spacing in inches.
- Enter roof pitch as rise over run.
- Add permanent dead loads for roof, ceiling, and truss weight.
- Add live, snow, and uplift values from local design information.
- Adjust load factors when your design method requires different combinations.
- Press calculate, then review reactions, uplift, and chord demand above the form.
- Use the CSV or PDF buttons to save the report.
Roof Truss Load Planning Guide
Start With a Clear Load Path
Roof truss loading starts with a clear model. A truss carries roof weight to exterior walls. The calculator uses the roof span, length, pitch, and spacing to estimate this path. It converts surface dead loads to horizontal load when the roof is sloped. This helps compare roofs with different pitches.
Know Each Load Type
Dead load is the permanent weight. It includes sheathing, shingles, tiles, ceiling, insulation, and truss self weight. Live load is temporary. It may include workers, equipment, or stored materials during construction. Snow load is climate dependent. Wind uplift acts upward, so it must be checked separately.
Spacing Changes Demand
Spacing has a strong effect. Wider spacing gives each truss more tributary area. That raises the pounds per truss and the wall reaction. Closer spacing lowers the demand on each truss. It may increase the number of trusses. The tool shows both individual truss demand and total roof demand.
Pitch Affects Surface Load
Pitch also matters. A steep roof has more sloped surface area. Surface based material weight increases with the slope factor. Snow behavior can also change with pitch, exposure, heat loss, and drifting. Always confirm local snow rules before final design.
Review the Engineering Indicators
The calculator estimates line load in pounds per foot. It also estimates support reactions, uplift reactions, maximum moment, chord force, and panel point load. These values help with early planning. They are useful for cost checks and layout discussions. They do not replace an engineered truss design.
Use Conservative Assumptions
Use conservative inputs for important projects. Add allowances for future roofing layers, solar panels, mechanical equipment, and ceiling changes. Check bearing walls, anchors, hurricane ties, and uplift connections. For permits, stamped drawings, or unusual roofs, consult a licensed structural professional. Good early estimates reduce surprises. They also improve communication with builders, suppliers, and inspectors.
Share Clean Project Notes
Good load planning also supports safer ordering. Truss suppliers may ask for span, pitch, overhang, spacing, roof covering, ceiling load, and environmental loads. Clean numbers reduce revisions. They also help identify heavy roof zones early. Valleys, dormers, parapets, skylights, and equipment curbs can create concentrated forces. Model those areas separately. Then share assumptions with the project engineer. Keep records of all assumptions. Clear notes make later design reviews faster and more accurate for everyone.
FAQs
1. What is a roof truss load?
A roof truss load is the weight or force carried by one truss. It includes permanent materials, temporary roof live load, snow load, and wind uplift. The load transfers from roof sheathing to trusses, then to bearing walls.
2. What does truss spacing change?
Truss spacing changes the tributary width. Wider spacing gives each truss more roof area to carry. This increases line load, reactions, and member demand. Narrower spacing usually lowers demand per truss.
3. Why does pitch affect the dead load?
Pitch increases the sloped roof surface area. Some material weights act on that sloped surface. The calculator uses a slope factor to convert those surface weights into horizontal design load.
4. Is snow load always added to live load?
Not always. Some design methods use different load combinations. This calculator lets you enter factors for a broad preliminary check. Always follow the required local code and engineering method.
5. What is net uplift reaction?
Net uplift reaction is the upward force left after stabilizing dead load is considered. It helps size anchors, clips, straps, and tie-down paths. It is important in high wind areas.
6. Can this replace truss shop drawings?
No. It is a planning calculator. Truss members, plates, bracing, bearing, and connections need detailed design. Use sealed shop drawings when required by the project or authority.
7. What is chord force?
Chord force is an estimated axial force in the top or bottom chord. The calculator approximates it from moment divided by truss depth. Real truss analysis depends on geometry and joint layout.
8. Which units does this tool use?
The tool uses feet, inches, psf, plf, pounds, and kips. Keep inputs consistent. Convert metric project values before entry to avoid incorrect results.