DIY 12x18 Lean-To Storage Shed Plan

The full plan is $19.99: buy the 12×18 lean-to shed plan. Or start with the free 12×18 lean-to shed plan PDF.

12×18 lean-to shed size, heights and openings

The door sits in the 18 ft front wall, the tall side. Rain runs off the 18 ft back edge.

What the 12×18 lean to shed plans include

The shopping list gives the quantity of every item, and the cut list gives every part’s length and count. The side walls step down from 9′ 7 1/8″ to 6′ 8″, so each side-wall stud is a different length; the cut list spells them out. The front wall is taller than 8 ft, so its studs are 9′ 2 5/8″ and the siding takes 4×10 sheets across the front. Nothing on the list is longer than 16 ft: the 18 ft skids and rim joists are spliced, and the plan marks each splice.

Building 18 ft long from 16 ft stock

Nothing on the shopping list is longer than 16 ft. Each 18 ft skid is spliced from two pieces, 10′ 8″ and 7′ 4″, and every splice is scabbed on both sides with a 3 ft pressure-treated 2×4. The 18 ft rim joists are spliced too, with a second joist at the rim joint so both ends of each piece land on solid wood. The front and back wall plates are cut in sections to match the wall lifts, and the second top plate is cut so its joint lands away from the joint below it, which ties the sections together.

How the walls go up

Each wall is framed flat on the deck, raised as a bare frame, braced plumb, and sided after all four stand. The plan sets stop posts on the rim so a tall wall stops at plumb and cannot kick out over the deck edge, and it puts the front wall braces about 7 ft up, where you can reach them from the deck.

Two people raise every section. The floor frame itself weighs about 490 lb once nailed, so you build it in place on the skids and square it to matching 21′ 7 5/8″ diagonals.

What is on the 12×18 lean-to shed material list

The shopping list is split by stage and gives the stock lengths:

• Foundation and floor: 4×4 skid pieces, pressure-treated 2×4 splice scabs, 2×6 rims and 16 joists, 7 sheets of tongue and groove plywood and a 1×4 filler strip for the rim.
• Pad: about 4.9 cu yd of 3/4″ stone, loose before tamping, plus the 4×6 frame, rebar stakes and timber spikes.
• Walls: 2×4 studs and plates, a doubled 2×8 front header and a doubled 2×6 back header, and 16 sheets of T1-11 in 4×8 and 4×10 sizes plus a 4×9 pair for the side walls.
• Roof: 17 2×6 x 16 ft boards for the rafters and fly rafters, blocking, 10 sheets of OSB, 2 rolls of felt, 10 bundles of shingles and 8 pieces of drip edge.
• Door, window and trim: 2 new T1-11 sheets for the door leaves, 6 T-strap hinges, a handle and latch, 2 barrel bolts, the prefabricated window, 1×8 fascia, 1×4 casing and corner trim.
• Hardware: nails by the pound, 26 hurricane ties, 4 framing angles, 4 twist straps, 8 ground anchors with straps, adhesive, flashing tape and 6 gallons of paint.

How the 12×18 lean-to roof is framed

With no ridge, a single-slope roof needs no collar ties, and the hurricane ties hold it down in wind.

• Two birdsmouths. Each rafter hooks over both walls. Both notches are a 3 1/2″ level seat with a 7/8″ plumb heel, about 15% of the rafter’s depth. Never cut deeper than one third.
• Pattern first. Cut one pattern from a straight 2×6, test it on both walls, check the 11′ 8 1/2″ level distance between the heels, then cut the other 14 and the 2 fly rafters.
• Three people per rafter. One stands on a front step ladder, one works from the deck at the low back wall, and one feeds the board from the doorway. Each board weighs about 40 lb, and the plan has its own handoff steps.
• Layout. The end rafters sit flush with each end, the rest 16″ on center, and the blocking is 4 3/4″ tall over each wall.
• Low pitch, double felt. Drip edge goes under the felt at the low eave and over it on the rakes and high edge.

Free 12×18 lean-to plans vs the paid PDF

The free 3DSHEDPLANS preview PDF lets you see the plan format before you pay. The paid 78-page plan has 19 build sections, the full shopping list with quantities, the cut list, 3D step views and close-ups of the key joints, and pro tips throughout the build. It arrives by email after checkout and has a 30-day money-back guarantee.

What fits in a 12×18 lean-to shed

• Lawn and garden. With the ramp at the door, a push mower, wheelbarrow, tiller and spreader roll in through the 72 in rough opening. The back wall is 6′ 8″ high, a good height for shelves of soil, seed and pots.
• Mower parking. The fit drawing parks a 42 in deck rider nose in, 4′ 7 3/16″ wide, with 8 1/8″ to spare on each side of the door and a 3′ 6″ aisle behind it to the 24 in deep back shelves. A 48 in deck fits with its deflector raised; a 54 in deck does not.
• Tall gear. Clear height is greatest near the front wall, 9′ 4 1/8″ under the plates, so stand ladders and long-handled tools there.

Before you build

• Face the low side away from your house, fence or paths, toward ground that drains. A gutter on the back edge helps on wet sites.
• Foundation. Build the 20 ft by 14 ft gravel pad inside its pressure-treated 4×6 frame, with a separate landing at the door, and set the skids level both ways. Our shed foundation guide compares other bases.
• Ramp. The deck sits 9 3/4 in above grade. The detachable ramp is 6′ 9″ wide and projects 3′ 6″ at 1:6. Keep 10 ft clear and level in front of the wall for a straight approach.
• Underlayment. At 3/12, asphalt shingles need double underlayment, and the plan lists two rolls of felt for it, per the Asphalt Roofing Manufacturers Association.
• Snow and wind. The 2×6 rafters span 11′ 5″ clear between bearing walls. The plan specifies #2 SPF or Douglas fir-larch for its 30 psf ground snow assumption (Southern pine #2 spans less, so go up one size), and includes hurricane ties, end-rafter angles and eight ground anchors. For local loads and exposure, check your local permit office.
• Permits. Size, height and setback rules vary by town and HOA, and some towns ask for drawings, so check your local permit office.
• Walls and rafters. The front and back walls are each raised in 2 sections by 2 people, the heaviest about 200 lb bare. Three people set each rafter, about 40 lb each, with the plan’s own handoff steps from an 8 ft step ladder.
• Tools. Circular saw, speed square, drill driver, framing hammer or nailer, 4 ft level, tape measure and a helper for every lift. Two 8 ft step ladders, or a rolling scaffold tower, reach the front wall and eave. A 20 ft extension ladder reaches the high edge, about 11′ 2″ up. You also need two swivel-pad bar clamps with at least 12 in clear opening.

Related plans

• A shorter lean-to: the 12×16 lean-to shed plan or the 12×14 lean-to shed plan.
• 6 ft longer, same depth: the 12×24 lean-to shed plan.
• 2 ft deeper: the 14×20 lean-to shed plan.
• Every size on the lean-to shed plans page.