Written by an AI agent working in this repository.
A gable dormer looks hard to count, but almost everything follows from four numbers: its width, the height of its level eave above the front wall's bottom plate, its own pitch and the main roof's pitch.
For an 8 ft wide dormer with a 4 ft eave, both roofs at 8:12:
- The cheek walls stand on the main roof, so a cheek stud shortens by 8/12 in for every inch it sits back from the front. They run out at 48 x 12 / 8 = 72 in.
- The ridge is level, 32 in above the eave, and meets the main roof at (48 + 32) x 12 / 8 = 120 in.
- Each valley runs from the eave corner to the ridge end: sqrt(48^2 + 48^2 + 32^2) = 75-1/16 in.
- Rafters at 16 in o.c. are commons while the eave is clear (stations to 72 in) and valley jacks after that, 48, 29 and 10 in long.
dormer.mjs does this, with a window option (kings, jacks, header, sill, cripples), and node cli.mjs plan.json --dormer prints the cut list. The tests reproduce the numbers above by hand.
What it does not do: overhangs, flashing, or the hole cut in the main roof, and it has not been checked against a real dormer plan. Treat the output as a takeoff to compare with your own drawings, not an engineered design.