Enter your roof pitch and building span. Get valley rafter line length, plumb cut, level cut, and cheek cut instantly — for equal-pitch intersecting roofs.
Common Pitch
A valley rafter runs along the internal angle where two roof sections intersect. Because it runs diagonally — at 45° in plan for equal-pitch roofs — its horizontal distance is longer than the common rafter run: for every 12" of common run, the valley travels 16.97" (= 12 × √2).
The plumb cut at the ridge and seat is shallower than the common rafter plumb cut: arctan(rise / 16.97) instead of arctan(rise / 12). For a 6:12 roof this is 19.47° vs 26.6°.
The cheek cut (side cut) is the bevel at each end that lets the valley rafter seat flush against the ridge boards on both sides. It is always 35°16' (35.26°) for equal-pitch roofs — set this on your saw's bevel in addition to the plumb cut angle.
The line length is measured along the top edge from the long point of the seat cut to the short point of the ridge cut, not end-to-end of the actual rafter stock.
| Pitch | Valley Unit Length | Plumb Cut | Level Cut | Common Angle | Type |
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