Roof Truss Input Form
Example Data Table
| Project | Span | Pitch | Spacing | Dead Load | Live Load |
|---|---|---|---|---|---|
| Garage mono roof | 20 ft | 3:12 | 2 ft | 10 psf | 20 psf |
| Workshop lean-to | 16 ft | 2.5:12 | 2 ft | 12 psf | 25 psf |
| Patio cover | 12 ft | 2:12 | 1.33 ft | 8 psf | 15 psf |
Formula Used
Pitch ratio: rise per 12 divided by 12.
Rise: horizontal span multiplied by pitch ratio.
Top chord length: square root of span squared plus rise squared.
Roof area: sloped roof length multiplied by building roof length.
Truss count: roof length divided by spacing, rounded up, plus one end truss.
Gravity load per truss: total load psf multiplied by tributary plan area.
Reaction per bearing: gravity load per truss divided by two.
Maximum moment: uniform line load multiplied by span squared, divided by eight.
Estimated lumber: top chord plus bottom chord plus estimated web length, then multiplied by truss count and waste.
How to Use This Calculator
- Enter the horizontal span between bearing points.
- Add the total roof length along the building.
- Select pitch input as rise per 12 or angle.
- Enter low and high side overhangs if needed.
- Add truss spacing, dead load, live load, and uplift load.
- Adjust waste, web factor, and cost per foot for budget planning.
- Press the calculate button.
- Review geometry, loads, reactions, materials, and warnings.
- Download the results as CSV or PDF.
Mono Pitch Roof Truss Planning Guide
What a Mono Pitch Truss Does
A mono pitch roof truss supports a single sloping roof plane. It is common on lean-to additions, modern homes, sheds, workshops, carports, and utility buildings. The shape looks simple, but the geometry affects drainage, wall heights, member length, roof area, load path, and material cost. This calculator helps convert common project inputs into practical early design values.
Why Geometry Matters
The most important values are span, pitch, rise, and top chord length. Span is the horizontal distance between supports. Pitch describes how much the roof rises over a fixed horizontal run. A steeper pitch increases rise and top chord length. It can improve drainage, but it may also increase wall height, bracing needs, cladding area, and installation difficulty.
Load Estimating Basics
Roof loads are usually entered as pounds per square foot. Dead load includes roofing, sheathing, insulation, ceiling materials, and the truss weight itself. Live load can include construction load, maintenance load, or snow load. Wind uplift acts in the opposite direction. This tool estimates tributary load by multiplying plan area by the selected spacing. It then gives bearing reactions, line load, shear, and a simple moment value.
Material and Budget Planning
The lumber estimate is not a shop drawing. It is a planning quantity. It adds the top chord, bottom chord, and an estimated web member allowance. The web factor lets you adjust the estimate for a simple or complex web layout. Waste percentage covers cutting loss, defects, and small changes during fabrication. Cost per foot gives a quick budget number before quotes are requested.
Design Caution
Mono pitch trusses must resist bending, compression, tension, sliding, and uplift. Bearings, fasteners, connectors, lateral bracing, and local code rules matter. Large spans, low slopes, heavy snow regions, high wind zones, and unusual roof materials need professional review. Use this calculator for planning, comparison, and discussion. Final member sizes and connection details should be verified by a qualified designer or engineer.
FAQs
What is a mono pitch roof truss?
It is a truss that supports one sloping roof plane. It usually has one low bearing side and one high bearing side.
Can this calculator size structural members?
No. It estimates geometry, loads, reactions, and material length. Final member sizing should be checked by a qualified professional.
What pitch should I use?
Pitch depends on drainage, roof covering, climate, and design style. Always check the minimum slope allowed for your roofing material.
Why does truss spacing affect load?
Each truss supports a strip of roof. Wider spacing gives each truss more tributary area, which increases the load per truss.
What is dead load?
Dead load is the permanent weight of roof materials. It includes sheathing, roofing, insulation, ceiling finish, and framing weight.
What is live load?
Live load is temporary or environmental load. It may include snow, maintenance activity, or construction loading during roof work.
Why is wind uplift included?
Wind can pull the roof upward. Uplift checks help identify when hold-downs, anchors, and connection design need closer review.
Is the lumber estimate exact?
No. It is a planning estimate. Actual shop drawings, web layout, splice needs, grades, and cutting methods can change quantities.