Skillion Roof On Ledger

A single-slope roof framed with site-cut rafters that bear on the low wall plate with a bird's mouth and are fixed at the upper end to a ledger beam on the high wall. Plan length and rafter run to the ledger, Pitch, largest rafter spacing and eave overhang, Rafter section and wall plate width, Ledger beam thickness and depth, Wall height

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
Ledger Thickness	70	mm
Ledger Depth	240	mm
Wall Height	2400	mm
Width	run + overhang + ledgerThickness + seatWidth	mm
Depth	length	mm
Height	ledgerTop + wallHeight	mm
Slope	Math.tan(pitch * Math.PI / 180)
Notch Height	seatWidth * slope	mm
Band Height	rafterDepth * Math.sqrt(1 + slope * slope)	mm
Ledger Top	slope * run - notch + bandHeight	mm
Intervals	Math.ceil((length - rafterThickness) / maximumSpacing)