Jack Rafter
A sawn timber rafter that runs from the wall plate up to a hip or valley rafter, with a bird's mouth seat, an eave tail and a vertical angled cut at its upper end.
Details
Category: Roof Framing › Straight Truss Roofs › Roof Members
By Huu Khanh Nguyen · Updated November 4, 2026
Parameters
| Name | Default | Unit |
|---|---|---|
| Run | 1800 | mm |
| Pitch | 25 | ° |
| Overhang | 450 | mm |
| Seat Width | 88.9 | mm |
| Depth | 190 | mm |
| Length | axisRun + axisOverhang | mm |
| Thickness | 45 | mm |
| Height | slope * (axisRun + axisOverhang) + bandHeight - (overhang > 0 ? 0 : notch) | mm |
| Slope | Math.tan((pitch * Math.PI / 180)) | |
| Axis Run | run + sizeY / 2 | mm |
| Axis Overhang | overhang | mm |
| Seat Length | seatWidth | mm |
| Notch Height | seatLength * slope | mm |
| Band Height | depth * Math.sqrt(1 + slope * slope) | mm |