Lean-tos, porches and wings

A lean-to is a single slope off a main wall on a ledger, with its own column line, beam and rafters. A gable porch projects with its ridge across the main wall, on its own columns and beams, with an optional decorative king-post timber truss. An enclosed wing is a sheeted lean-to at eave height, and a wrap is two enclosed legs meeting at a corner. Any of the four works on any wall.

Columns, beams, ledgers, rafters, purlins, ledger lags and decorative timber come out as their own lines rather than being absorbed into the main building's framing. The porch is where a quote leaks most often, because it is the part that gets added last and estimated by feel.

The foundation pass runs after the additions are merged in, so a lean-to or porch column is drawn embedded on a footing pad inside a poured collar exactly like a wall post — and the post-hole concrete, the pads and the uplift restraint are on the order. This is the concrete that goes missing when the porch is drawn separately from the building.

Additions anchor to their wall the way openings do, and the rules are stated: butt or bury, nothing breaks the roof plane, joints are cut rather than collided, and an addition may never cut into the main building's eave or rake overhang. Earlier versions started at the wall line, which sits behind the skin, so ledgers, beams and roof planes ran straight out through the steel in every render.

A lean-to on a sidewall takes over that stretch of main eave, so the trough breaks around it and the leftover stubs overlap the lean-to by a foot rather than dying on its first rafter. Downspouts drop at building corners, never at a lean-to junction, and lean-to and porch drops sit on the end 6x6s. Linear feet follow the roof you actually drew, including whatever is hung off it.