Collar-Tie Rafter Roof
A gable roof framed with site-cut rafters in pairs that meet at a ridge board, each pair tied across the wall plates by a ceiling joist and braced across the upper third of the attic space by collar ties. Plan length and span over the wall plates, Pitch, largest rafter spacing and overhang, Rafter, ceiling joist and ridge board sections, Collar tie section, height and largest 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 |
| Span | 7000 | mm |
| Pitch | 25 | ° |
| Maximum Rafter Spacing | 600 | mm |
| Overhang | 450 | mm |
| Rafter Thickness | 45 | mm |
| Rafter Depth | 190 | mm |
| Wall Plate Width | 88.9 | mm |
| Ceiling Joist Thickness | 45 | mm |
| Ceiling Joist Depth | 140 | mm |
| Ridge Board Thickness | 19 | mm |
| Collar Tie Depth | 140 | mm |
| Collar Tie Height | 2 * atticHeight / 3 | mm |
| Maximum Collar Tie Spacing | 1219.2 | mm |
| Width | span + 2 * overhang | mm |
| Depth | length | mm |
| Height | Math.max(atticHeight + bandHeight, joistDepth) - (overhang > 0 ? -notch - overhang * slope : 0) | mm |
| Slope | Math.tan(pitch * Math.PI / 180) | |
| Rafter Run | (span - ridgeThickness) / 2 | mm |
| Notch Height | seatWidth * slope | mm |
| Band Height | rafterDepth * Math.sqrt(1 + slope * slope) | mm |
| Attic Height | slope * run - notch | mm |
| Collar Tie Thickness | collarDepth == 140 ? 19 : 45 | mm |
| Collar Tie Setback | (collarHeight + notch) / slope | mm |
| Intervals | Math.ceil((length - rafterThickness - joistThickness) / maximumSpacing) | |
| Unit Spacing | (length - rafterThickness - joistThickness) / intervals | mm |
| Collar Tie Stride | Math.min(intervals, Math.max(1, Math.min(3, Math.floor(collarSpacing / pitchStep)))) |