Enter Truss and Load Details
Example Data Table
| Span | Pitch | Overhang | Spacing | Load | One Side Chord | Use Case |
|---|---|---|---|---|---|---|
| 24 ft | 4 / 12 | 1 ft | 24 in | 35 psf | 13.70 ft | Small garage roof |
| 36 ft | 6 / 12 | 1.5 ft | 24 in | 45 psf | 21.80 ft | General building truss |
| 48 ft | 8 / 12 | 2 ft | 16 in | 55 psf | 31.25 ft | Wide span roof |
Formula Used
Half run: Span ÷ 2
Run to tail: Half run + overhang
Slope ratio: Pitch rise ÷ 12
Top chord length: √(run to tail² + vertical rise along run²)
Slope angle: atan(pitch rise ÷ 12)
Projected tributary area: Projected roof width × truss spacing
Gross vertical load: Total gravity load psf × projected tributary area
Bearing reaction: Net vertical load ÷ 2
Estimated compression: Bearing reaction ÷ sin(slope angle)
Compression stress: Estimated compression ÷ chord section area
Stress utilization: Compression stress ÷ adjusted allowable compression × 100
The compression calculation is an early planning estimate. Real truss forces depend on web layout, support conditions, connection design, load combinations, and local code rules.
How to Use This Calculator
- Enter the clear span between supports.
- Add the overhang length for each side.
- Enter the roof pitch as rise per 12 inches of run.
- Add heel height, spacing, and design loads.
- Enter chord size and allowable compression data.
- Use custom unbraced length when bracing differs from panel spacing.
- Press the calculate button.
- Review geometry, load, compression, slenderness, and cost outputs.
- Download the result as CSV or PDF for records.
Planning Truss Top Chords
Why the Top Chord Matters
The top chord is a main sloping member in a roof truss. It follows the roof pitch from the bearing area toward the ridge. It helps carry roof sheathing, roofing, ceiling transfer loads, snow, workers, and wind effects. A small change in span, pitch, or overhang can change its length. It can also change the force that moves through the member.
Geometry Comes First
Good truss planning starts with geometry. The span sets the half run. The pitch sets the vertical rise. The overhang adds extra sloping length beyond the wall line. This calculator combines those inputs and returns the estimated top chord length. It also gives the slope angle and ridge height. These values help with early sketches, takeoffs, and layout checks.
Loads and Compression
A top chord usually works in compression under gravity loads. The calculator estimates dead, live, and snow loads over the projected tributary area. It also lets you deduct a wind uplift value. The net load is divided into two bearing reactions. Then a simplified compression estimate is made from the roof angle. This gives a helpful first look at member demand.
Section Checks
The calculator compares estimated compression stress with an adjusted allowable value. It also checks a simple slenderness ratio using the unbraced length and weak member dimension. These checks do not replace engineered design. They are useful for spotting obvious problems before detailed drawings are prepared.
Practical Use
Use the results for budgeting, roof framing discussions, and rough material estimates. The total top chord stock value helps estimate board length. The cost field helps build a quick material allowance. Always confirm final truss design with a licensed professional or truss manufacturer. Truss plates, web forces, bracing, bearing, uplift anchorage, and code load combinations need proper review.
FAQs
1. What does a truss top chord calculator do?
It estimates top chord length, slope angle, rise, basic load effects, compression stress, slenderness, and material cost from common truss planning inputs.
2. Is this calculator suitable for final structural design?
No. It is for planning and early checks only. Final truss design should be completed or verified by a qualified engineer or truss manufacturer.
3. What pitch format should I enter?
Enter the rise per 12 inches of horizontal run. For example, a 6:12 roof pitch should be entered as 6.
4. Does the calculator include overhang?
Yes. It adds the overhang to the half span before calculating the sloped top chord length from ridge to tail.
5. What is the service factor?
The service factor adjusts the allowable compression value. Use 1.00 for no adjustment, or another value when your design basis requires it.
6. What is custom unbraced length?
It is the unsupported top chord length used for slenderness checking. Enter 0 when you want the calculator to estimate it from panel count.
7. Why does compression increase on low pitch roofs?
Low pitch roofs have a smaller slope angle. In the simplified model, a smaller angle can create higher estimated axial compression.
8. Can I export my result?
Yes. After submitting the form, use the CSV or PDF button above the form to save the calculated output.