Framing a 4×8 Lean-To Shed Against an Existing Shed: Walls to Doors

A 4 ft x 8 ft lean-to shed is framed against an existing shed in this first part of a build, with the tall back wall cut to 99 in so 8 ft plywood and lumber can be stored against it.

Walls

The back wall studs are 2x4s spaced 16 in on center, joined with three 3 in nails at each end from a framing nailer; 3 in construction screws work too. The front wall is the same width but 8 ft high, with a centered door opening. Two jack studs 82 in high set the doorway height, and the header is reinforced with seven scrap 2×4 pieces cut from one template, in a truss-like arrangement.

The finished width is 48 in before sheathing. The side wall plates are cut to 41 in because they fit between the front and back walls, each 3 1/2 in thick. Side wall studs are spaced 12 in on center.

Back wall

The back wall is sheathed with 3/8 in plywood, matching the existing shed, before it goes up, since it will sit against the shed. A second center stud gives the second panel something to screw into. Two 6 in tall panels cap the top. After it was lifted into place, it was plumbed and fixed to the shed's 2×4 framing with lag screws, recessed about 3/4 in with a Forstner bit because the screws were slightly short. The side walls attach with butt joints, checked with a level, and the front wall was clamped before nailing.

Roof

A ledger board goes on the back wall, flush on the left and extending 24 in on the right. The existing roof pitch is about 7 degrees, but the gap suggested a steeper slope, so the rafter ends are cut at 8 degrees using a speed square. The bird's mouth is marked with the square, cut with a circular saw and finished with a jigsaw. The first rafter cut about an eighth of an inch too far on one side, so the adjustment was applied to the template. The overhang is 9 in, and seven rafters are needed.

The rafters are toenailed, with Simpson Strong-Tie brackets as an option. Blocking goes under the rafters on the side walls, and 24 in blocks support the overhang. A sub fascia board matches the existing shed.

Doors

Two doors, each about 32 3/8 in wide, match the larger shed. Each has three hinges, at the top, bottom and center. A 1/4 to 1/2 in gap is kept between the doors. The lumber was wet and warped as it dried, so center hinges help keep things aligned. Trim and finishing come in part two.