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Calculate roof truss dimensions, member forces, and lumber requirements. Supports King Post, Queen Post, Fink (W), Howe, Pratt, and Attic truss types.
Select truss configuration
Distance from wall to wall
Format: rise/run (e.g., 6/12)
Roof weight
Maintenance load
Regional snow load
Design wind speed
On center spacing
Eave overhang
Building length (optional)
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Single vertical post in center with angled struts. Best for small to medium spans (20-40 ft).
Two vertical posts with horizontal tie beam. Best for medium spans (40-60 ft).
Inverted W pattern under chord. Most common modern truss for residential.
Vertical web members with angled compression members. Good for heavy loads.
Vertical web members are in tension, diagonals in compression. Efficient design.
Creates usable attic space with near-horizontal bottom chord. Less structural capacity.
| Pitch | Angle | Multiplier | Type | Common Use |
|---|---|---|---|---|
| 2/12 | 9.46° | 1.014 | Low Slope | Commercial, flat roofs |
| 4/12 | 18.43° | 1.054 | Medium Low | Coastal areas |
| 5/12 | 22.62° | 1.083 | Medium | Good drainage |
| 6/12 | 26.57° | 1.118 | Medium | Standard residential |
| 8/12 | 33.69° | 1.202 | Medium Steep | Heavy snow regions |
| 10/12 | 39.81° | 1.302 | Steep | Very heavy snow |
| 12/12 | 45.00° | 1.414 | Very Steep | Mountain areas |
Engineered trusses are computer-designed and factory-built to precise specifications with stamped structural calculations. Site-built trusses are built on-site with less precision. Engineered trusses are more reliable and cost-effective for most applications.
Common spacings are 16", 24", and 48" on center. 24" OC is most common for residential. Narrower spacing (16") provides more support; wider spacing (48") reduces labor but may require stronger members. Check local building codes.
Use a level and measuring tape: place the level horizontally against a rafter, mark 12 inches along the level, measure vertically to the rafter. That measurement is your rise for a 12" run. Or use a digital pitch gauge for accuracy.
Dead load is typically 10-20 psf (roof weight). Live load is usually 20 psf. Snow load varies by region: check your local building code. Wind load depends on exposure and building location. Consult a structural engineer for your specific area.
Compression means the member is being pushed (squeezed). Tension means the member is being pulled. Different truss types distribute these forces differently. The top chord typically sees compression; bottom chord sees tension.
No - modifying or cutting trusses compromises their structural integrity. Any changes must be done by a structural engineer and may require new calculations. Plan ahead if you need attic space or ceiling openings.
Temporary braces stabilize trusses during installation until permanent bracing and sheathing are in place. They prevent tipping and collapse during construction. Remove them only after permanent bracing is installed.
Divide your roof length by truss spacing (in feet). For example: 60 ft roof ÷ 2 ft spacing (24" OC) = 30 trusses. Always round up and add extra for waste. Include end trusses.