Valley Rafter Roof

An L-shaped roof framed with site-cut members: a main gable and a wing gable of the same span and pitch meeting in two valleys, with common rafters, valley rafters, valley jack rafters and a ridge board on each roof. Main length, span and wing length over the wall plates, Pitch and largest rafter spacing, Common rafter, valley rafter and ridge board sections, Wall height

Details

Category: Roof Framing › Timber Roof Framing › Hip and Valley Roofs

By Huu Khanh Nguyen · Updated November 5, 2026

Parameters

Name	Default	Unit
Length	9000	mm
Span	7000	mm
Wing Length	2000	mm
Pitch	25	°
Maximum Rafter Spacing	600	mm
Rafter Thickness	45	mm
Rafter Depth	190	mm
Valley Rafter Thickness	45	mm
Valley Rafter Depth	240	mm
Wall Plate Width	88.9	mm
Ridge Board Thickness	19	mm
Wall Height	2400	mm
Width	span + wingLength	mm
Depth	length + hipFace / 2	mm
Height	atticHeight + Math.max(bandHeight, hipDepth * Math.sqrt(1 + slope * slope / 2)) + wallHeight	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
Valley Face Offset	hipThickness / Math.SQRT2	mm
Main Intervals	Math.ceil((length - rafterThickness) / maximumSpacing)
Main Unit Spacing	(length - rafterThickness) / mainIntervals	mm
First Back Rafter	Math.ceil(span / mainStep - 1e-9)
Main Jacks Valley 1	span / 2 - ridgeThickness / 2 - hipFace - 3 * rafterThickness / 2 >= 0 ? Math.floor((span / 2 - ridgeThickness / 2 - hipFace - 3 * rafterThickness / 2) / mainStep + 1e-9) + 1 : 0
First Main Jack Valley 2	Math.ceil(((span / 2 + ridgeThickness / 2) + hipFace + rafterThickness / 2) / mainStep - 1e-9)
Main Jacks Valley 2	Math.max(0, backFirst - jackSecond)
Wing Grid Start	(span / 2 + ridgeThickness / 2)	mm
Wing Intervals	Math.ceil((span + wingLength - rafterThickness - wingStart) / maximumSpacing)
Wing Unit Spacing	(span + wingLength - rafterThickness - wingStart) / wingIntervals	mm
First Wing Common	Math.ceil((span - wingStart) / wingStep - 1e-9)
First Wing Jack	Math.ceil((hipFace + rafterThickness / 2) / wingStep - 1e-9)
Wing Jacks	Math.max(0, wingBack - wingJackFirst)