Shed Rafter Planning Guide
A shed roof looks simple, yet small errors matter. Each rafter must match the same rise, run, and slope. The calculator gives a repeatable layout before cutting starts. It helps compare pitch, overhang, spacing, and waste. Use it during sketching, pricing, and final material checks.
Why Rafter Length Matters
Rafter length controls roof line, drainage, fascia position, and board choice. A board that is too short cannot be safely stretched. A board that is too long creates extra cutting and waste. The main length is based on the horizontal run. Pitch then converts that run into a sloped length. Overhangs add tail length at each roof edge.
Important Shed Roof Terms
Run is the flat distance across the shed. Rise is the height gained over that run. Pitch shows rise for every twelve units of horizontal travel. The roof angle is the slope measured from level. Spacing is the center distance between neighboring rafters. Birdsmouth depth is the notch depth at the wall plate. Keep that notch modest, because deep notches weaken lumber.
Using Results On Site
Start by checking the building width and roof length. Measure outside wall plate to outside wall plate. Add the lower and upper overhangs if they will be cut from one rafter. Select a spacing that fits local loads and sheathing rules. Review the rafter count, then add extras for mistakes. Mark one test rafter first. Fit it on the shed before batch cutting. Use the same pattern for the remaining pieces.
Material And Cost Checks
The total linear material estimate includes waste. It is useful for ordering, not for structural approval. The stock board count assumes available boards meet the cut length. If the cut length exceeds stock length, choose longer lumber. Roof area helps estimate sheathing, underlayment, and roofing. The sheet count includes a waste allowance. Prices are optional. They help compare layouts before buying. Always confirm design with local code, span tables, and load requirements.
Layout Tips
Work from one reference edge. Keep crowns facing the same direction. Label lower tails and upper tails. Do not mix board widths in one roof row. Recheck diagonal measurements before fastening sheathing. Clean layout marks reduce errors on repeated cuts.