Enter Roof and Load Data
Use feet, inches, pounds per square foot, and pounds as labeled.
Example Data Table
This sample shows the input format and the calculator assumptions.
| Input | Example value | Purpose |
|---|---|---|
| Building plan | 40 ft × 28 ft | Creates the horizontal roof footprint. |
| Roof pitch | 6 in 12 | Converts plan area into sloped roof area. |
| Dead load | 18 psf | Applies to the sloped roof surface. |
| Snow load | 30 psf | Applies to the horizontal roof projection. |
| Wind uplift | 28 psf | Creates an upward preliminary demand. |
| Rafter spacing | 24 in | Estimates a common-rafter line load. |
Formula Used
These formulas provide a transparent preliminary load screen.
Df, Sf, Lrf, and Uf are user-entered factors. This page does not determine local code pressures, snow coefficients, wind zones, or required combinations.
How to Use This Calculator
- Measure the exterior plan length and width in feet.
- Enter the roof pitch rise for every twelve horizontal inches.
- Enter verified dead, snow, live, and uplift pressures.
- Set rafter spacing and any concentrated equipment load.
- Use project-specific factors, not default values blindly.
- Review gravity, uplift, and rafter results after calculation.
- Have a qualified designer verify the final roof system.
Understanding Hipped Roof Loads
Hipped roofs transfer weight through common rafters, hip rafters, ceiling ties, walls, and foundations. Their geometry differs from a simple gable roof. Hip rafters collect load from triangular roof sections. This affects load distribution. Accurate geometry keeps all later roof load comparisons meaningful.
Start with the building plan dimensions. The plan area establishes the horizontal footprint. The pitch then converts that footprint into sloped roof area. A steeper pitch creates more roof surface. It also increases dead load carried by the framing. Material weights should include sheathing, underlayment, roofing, insulation, ceiling finishes, and framing allowances. Use verified product weights.
Snow and roof live loads are normally considered over horizontal projection. This calculator keeps those loads separate from surface-area dead load. It compares snow and roof live load, then uses the governing value for a simplified gravity total. Local snow rules can require special adjustments. Drifting, unbalanced snow, exposure, thermal condition, and sliding snow may control in some locations.
Wind acts differently from gravity. Wind uplift tries to pull roof planes and connections upward. The calculator estimates a net uplift demand by reducing factored wind uplift with a limited stabilizing dead load. This is useful for a preliminary connection review. It does not replace zone-specific wind pressures, edge and corner coefficients, or engineered fastener schedules.
Common rafter values are also approximations. The displayed common-rafter line load uses the selected rafter spacing and the governing variable roof load. Hip rafters carry larger tributary areas than common rafters. Jack rafters transfer load into hip rafters. Those members need separate design checks for bending, shear, deflection, compression, and connection forces.
Review the result with the project drawings. Confirm the actual framing layout, ridge location, overhangs, openings, bearing points, and concentrated equipment loads. Units must remain consistent. Enter pressure values in pounds per square foot and lengths in feet. Enter rafter spacing in inches. A positive uplift pressure represents the upward design demand.
Use the factored gravity figure only as a screening value. Design load combinations depend on the adopted code, risk category, climate data, and engineer assumptions. A licensed structural professional should confirm member sizes, load paths, lateral resistance, and fastening details before construction begins. This calculator supports early estimating, comparison, and communication. It should never be the sole basis for a roof design.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates hipped roof geometry, gravity loads, wind uplift demand, and a common-rafter line load. It is intended for preliminary planning, estimating, and checking input consistency.
2. Does it select rafter or hip-rafter sizes?
No. Member sizing requires span, species, grade, support conditions, bracing, deflection limits, connections, and the adopted design standard.
3. Why are snow and roof live loads based on plan area?
These loads are commonly expressed on horizontal projection. Local rules may modify that basis for slope, exposure, drifting, snow retention, or special roof geometry.
4. Why is dead load based on sloped area?
Roofing, sheathing, and similar permanent materials cover the actual sloped surface. A steeper roof therefore has more surface area than its plan footprint.
5. What roof shape does the geometry assume?
It assumes a rectangular, symmetrical hipped roof with a uniform pitch. The ridge follows the longer building direction. Complex hips, unequal pitches, dormers, and offsets need separate analysis.
6. How should wind uplift pressure be entered?
Enter a positive upward pressure in pounds per square foot. Use pressures derived from the project design method. Edge and corner pressures often differ from field pressures.
7. What does the connection comparison mean?
It compares one entered capacity against the simplified total uplift demand. It does not distribute force among straps, clips, nails, anchors, or individual roof zones.
8. Can equipment load be included?
Yes. Enter the total added equipment weight. Confirm where the equipment bears. A concentrated load often requires local framing checks beyond a roof-wide calculation.
9. Why is the hip-rafter load not shown directly?
Hip rafters receive tributary load from jack rafters and roof planes. Their force pattern depends on layout, rafter spacing, support details, and member geometry.
10. Are the default load factors always correct?
No. They are editable examples only. Apply combinations and factors required by the governing code, loading standard, jurisdiction, and project engineer.
11. Can this be used for final construction design?
No. Use it as a preliminary screen. Final work should be reviewed by a qualified structural professional who verifies loads, members, connections, and complete load paths.