Skillion Roof On Walls With Purlins
A single-slope roof framed with site-cut rafters on the low wall plate and a beam on the high wall, with purlins laid flat across the rafters for the cladding. Plan length and rafter run to the high wall beam, Pitch, largest rafter spacing and eave overhang, Rafter section, plate width and high wall beam section, Purlin width, wind zone and largest purlin spacing
Details
Category: Roof Framing › Timber Roof Framing › Gable and Skillion Roofs
By Huu Khanh Nguyen · Updated November 4, 2026
Parameters
| Name | Default | Unit |
|---|---|---|
| Length | 6000 | mm |
| Rafter Run | 3500 | mm |
| Pitch | 15 | ° |
| Maximum Rafter Spacing | 600 | mm |
| Overhang | 450 | mm |
| Rafter Thickness | 45 | mm |
| Rafter Depth | 190 | mm |
| Wall Plate Width | 88.9 | mm |
| High Wall Beam Thickness | 70 | mm |
| High Wall Beam Depth | 240 | mm |
| Purlin Width | 70 | mm |
| Purlin Thickness | 45 | mm |
| Wind Zone | 0 | |
| Maximum Purlin Spacing | 900 | mm |
| Width | run + overhang + beamThickness + purlinThickness * Math.sin(pitch * Math.PI / 180) | mm |
| Depth | length | mm |
| Height | beamTop + purlinThickness * Math.cos(pitch * Math.PI / 180) - Math.min(overhang > 0 ? -notch - overhang * slope : 0, beamTop - beamDepth) | mm |
| Slope | Math.tan(pitch * Math.PI / 180) | |
| Notch Height | seatWidth * slope | mm |
| Band Height | rafterDepth * Math.sqrt(1 + slope * slope) | mm |
| High Wall Beam Top | slope * run - notch + bandHeight | mm |
| Intervals | Math.ceil((length - rafterThickness) / maximumSpacing) | |
| Slope Length | (run + overhang) / Math.cos(pitch * Math.PI / 180) | mm |
| Purlin Intervals | Math.ceil((slopeLength - purlinWidth) / purlinSpacing) | |
| Purlin Spacing Along The Slope | (slopeLength - purlinWidth) / purlinIntervals | mm |