A rafter-framed lean-to: ledger against the main wall carrying the inboard rafter ends, a column line at the outboard edge, a beam across the column tops with rafters birdsmouthed over it, purlins on edge, skin on top, and an outboard subfascia whose depth is derived from the purlin and rafter stack.
Also called: side shed · equipment bay · open lean-to · shed roof addition
- 1The outer eave is DERIVED, never authored: attach elevation minus width times pitch over twelve.
- 2The inverse — 'I need N feet of clearance out there' — surfaces both bounds together, because a shallower pitch buys width but runs into the roofing minimum slope.
- 3Width ladders come from the research doc (8 to 24ft); rafter framing stops at 24ft, beyond which it becomes a mono-truss structure and a warning says so.
- 4A headroom floor of 6ft-6in at the outer eave is enforced, so the clamp cannot bury the columns underground.
- 5Vehicle clearance is called out as an info rule: 8ft for vehicle access, 10-12ft for equipment or an RV.
- 6Enclosed lean-tos get wall skin on the outboard column line.
A lean-to trades width for headroom — every extra foot out is less clearance at the outer eave — and that is the number a builder needs while dragging, not afterwards, so it is shown live. The old height check let a 9/12 pitch running 24ft out bury its own columns underground before anything complained. And a fascia sized without accounting for the purlin-and-rafter stack behind it left the rafter tails hanging below it as a row of teeth along the eave, so its depth is now derived from what it actually has to cover.
- Outer eave height guessed instead of derived from attach height, width and pitch.
- Lean-tos drawn wider than rafter framing supports.
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