8x20 Lean-To Storage Shed Plan

You can buy the 8×20 lean-to shed plan now, or open the free 8×20 lean-to shed plan PDF first and see how the drawings look. The door sits in the middle of the 20 ft front wall.

8×20 lean to shed plans: the numbers for a site check

The door is in the 20 ft front wall and the window in the back wall. The roof falls from the high front wall to the 6′ 8″ back wall.

Laying out the pad

Check with your permit office first for size, height and setback rules. Then call 811, the free call-before-you-dig line, a few working days before any stake goes in so the buried power, gas and water lines get marked.

Stake the corners, 20′ 0″ along the front and 8′ 0″ along the sides, and move one stake until both diagonals read 21′ 6 1/2″. Then strip the sod and roots over a 22′ x 10′ patch, a foot past the shed on every side so rain runs away from it. Digging knocks stakes around, so reset them and check the diagonals again.

The stone goes down 4″ deep, tamped in two layers, then raked level and checked with a long straight board and a level in several directions. The plan’s tip: a pad level within 1/4″ over its length saves hours later.

On a sloped yard you stretch a string with a line level from the highest stake to each of the others and measure down at each. A few inches of fall gets made up with more stone on the low side, tamped every 2″. Anything more and you either dig the high side down or set solid concrete blocks on compacted stone under the skids on the low side and shim them with pressure-treated shims. Check the finished pad with the string and the board before a skid goes down.

How the 8×20 lean-to shed goes together

The walls are the biggest block at 16 hours: four walls to frame, raise and brace, then side. The plan builds the front and back walls in two sections each so that two people can raise each one.

Splicing the skids and rims

The skids are longer than a 16 ft board, so the plan splices them. Each of the three skids is two boards butted end to end on the gravel: skids 1 and 3 are 8′ 0″ plus 12′ 0″ counting from the left end, and skid 2 is 12′ 0″ plus 8′ 0″, so the joints don’t line up. Every joint sits under a floor joist, at least 4 ft from the joint in the next skid, and gets a 3 ft pressure-treated 2×4 scab on both sides with six 3 1/2″ galvanized nails per scab. That’s six scabs for the whole foundation. The skids run along the 20 ft side, 3′ 10 1/4″ on center, with the outer two flush with the floor edges. They need to be ground-contact lumber (UC4A or higher), laid crown up so the weight of the floor flattens them out.

The two rim joists are spliced the same way, 9′ 4 3/4″ plus 10′ 7 1/4″, and the break lands over a doubled joist. That is why the joist count is 17 and not 16: the extra one is nailed tight against the layout joist at 9′ 3 1/4″ so the rim joint falls on the seam between the two and each rim end gets three nails into a full joist.

Clamp the two rims together and mark the joists on both at once: one joist flush at each end, then lines at 15 1/4″, 31 1/4″, 47 1/4″ and every 16″ after that. Start those marks at the left end seen from the front. The rafter marks start from the same end later, so the sheathing and soffit joints land on rafters.

Once it’s nailed the floor frame weighs about 380 lb and racks out of square if you lift it, so you never carry it. You build it right on the skids: stand each rim on edge over an outer skid, stand the 7′ 9″ joists between them on the marks, nail through the rims with three 3 1/2″ nails per joist, and push the long corner along the skids until both diagonals read 21′ 6 1/2″. Only then do you toe-nail it down at every crossing.

Five sheets of 3/4″ tongue and groove plywood cover the deck. A sheet only covers about 47 1/2″ once its tongue sits in the next groove, so two rows come to 7′ 11″ of the 8′ 0″ frame. That leaves 1″ along the back rim, which gets a strip of 1×4 ripped to 1″, glued and screwed flush with the outside face. The wall’s bottom plate covers it. The second row starts with a half sheet so the end joints stagger, and the plan maps every piece with a letter, A to F.

Raising the four walls

Every wall is framed flat on the deck, tipped up as a bare frame and braced plumb. Siding waits until all four stand and the corners are nailed.

The front wall goes first, while the whole deck is empty. You lay it with the bottom plate set back 3 1/2″ from the front edge (snap a chalk line), because the wall swings out to the edge as it tips up on the inside edge of that plate, and it lands flush. The wall is framed in two sections side by side, each with its own pieces of plate, and each one is a two-person lift. The second top plate, 20 ft in two pieces, waits until the walls stand. It bridges the section joint and laps it by at least 4 ft on each side, so each layer covers the other’s joint.

Before the lift you drive two or three nails part way through the bottom plate so it hinges instead of sliding, and nail two 12″ stop blocks to the outside of the rim, 2″ above the deck. Nobody stands on the ground in front of a wall going up. A wall that passes plumb falls outward, off the deck. Pick a calm day too, because a bare frame catches wind like a sail. The braces are 12 ft 2x4s running out from both ends to 2×4 stakes about 5 ft from the shed, so the deck stays clear for the next wall.

Section 1 of the front wall goes up first and lands flush with the front edge. Section 2 follows, tight against it, and you clamp the two joint studs flush and nail them together every 12″, staggered. The back wall goes up the same way, set back 3 1/2″ from the back edge, in sections of 11′ 11 1/4″ and 8′ 0 3/4″.

The two side walls are framed flat on the deck between the standing front and back walls. Their plates are 1/4″ shorter than the gap, so they tip up between them: check the front and back for plumb first, and if one is tight, tap it down against a block. Push each side wall tight to the front wall. The 1/4″ gap stays at the back corner, where a shim goes in at each nail when you join the walls. A diagonal brace stays tacked across each wall until just before that wall gets its siding. The plumb braces only stop a wall leaning in or out; the diagonal is what stops it racking.

Cutting the sloped side walls

The side walls follow the roof, so each of the seven studs in them is a different length, from 6′ 5 3/8″ at the back to 8′ 3 3/16″ at the front. Each top gets a 14 degree bevel through the 1 1/2″ thickness, square across the face, with the long point facing the tall front end. The sloped top plate is a long parallelogram, not a wedge: both ends get the same bevel and both edges measure 7′ 7 1/2″.

Mark the sloped plate from its own column in the stud table. The spacing stretches along a slope, and if you copy the bottom plate marks instead, the last stud ends up 2 11/16″ off plumb. A sloped wall has unequal diagonals too, so you square a rectangle instead: mark both end studs 6′ 0″ up and check that the two diagonals to the opposite bottom corners both read 9′ 6 5/16″.

The two side walls are mirror images, one starting its marks from the back end of the plate and the other from the front, so label them as you cut. The tallest two studs on each side come out of 10 ft boards and the rest from 8 footers.

What is on the 8×20 lean-to shed materials list

The shopping list is split by section, and every lumber line names the board length that wastes the least. The plan suggests adding 2 or 3 spare studs for bad boards.

For the foundation and floor you buy three pressure-treated 4×4 x 12 ft and three 4×4 x 8 ft for the skids, two 2×6 x 12 ft and two 2×6 x 10 ft for the rims, seventeen 2×6 x 8 ft joists, two 2×4 x 10 ft for the scabs and 5 sheets of 3/4″ tongue and groove plywood. The front wall takes seventeen 2×4 x 10 ft studs, five 2×4 x 14 ft boards for plates and trimmers, and a doubled 2×8 header over the door with 1/2″ plywood between the plies. The back wall’s 19 studs come out of ten 14 ft boards, two from each except the last. Siding is T1-11, sixteen sheets in all: five 4×9 for the front, five 4×8 for the back, two 4×8 and two 4×9 for the sides, and two more for the door leaves. No 4×9 at your store? The list says buy 4×10 and cut it to the same marked height.

The roof is eighteen 2×4 x 10 ft boards for the 16 rafters and the 2 fly rafters, three 2×4 x 12 ft and two 8 footers for the blocking and lookouts, 8 sheets of 7/16″ OSB, two rolls of 15 lb felt, 8 bundles of shingles and 8 pieces of drip edge. Fascia is 1×6, four 10 footers and two 12 footers.

The hardware list includes 29 lb of 16d galvanized framing nails, 28 hurricane ties, 4 framing angles for the end rafters, 4 twist straps for the wall corners, 8 tubes of construction adhesive and 5 gallons of exterior paint and primer in one for two coats. The ground anchors are on the list too, and they get their own section below.

Buying the lumber in stages

The plan gives quantities only, no prices, and lists them by section so each stage has its parts.

The sheet goods: 5 sheets of tongue and groove plywood, 16 of T1-11 counting the door leaves, 8 of OSB and two of 1/2″ plywood. The first 1/2″ sheet gives the header fillers and part of the soffit strips, and the second finishes the soffit strips, so rip the filler lanes first and keep the rest.

The double door and the window

The door opening is 5′ 0″ wide and 6′ 4 1/2″ tall, centered in the front wall (it runs from 7′ 6″ to 12′ 6″ from the left corner), with a king stud and a trimmer on each side. The bottom plate runs straight through it while the wall goes up and gets cut out flush with the trimmers once the siding is on, which leaves a framed height of 6′ 6″.

You build two leaves, each 2′ 5 5/8″ wide and 6′ 5 1/4″ tall, from two new sheets of T1-11, because the piece cut out of the opening is too short. A 1×4 frame of two stiles and three rails goes on the outside of each, then two Z braces cut on the miter saw at 29 degrees. Both braces rise from the hinge side toward the latch so they carry the weight into the hinges. The 1×4 casing goes around the opening first, so the hinges and stops land on top of it. Each leaf hangs on three T-strap hinges, and the 1×2 stop under the header is set back 5/8″ from the face of the siding so the closed leaves finish flush with the casing.

Only one leaf is the working door. The other is fixed with a barrel bolt at the top and one at the bottom, and a 1×2 astragal on its inside face, standing 3/4″ past the edge, gives the active leaf something to close against. The active leaf swings out, and the latch goes on it.

The window is a prefabricated unit made for a 36″ x 36″ rough opening (units usually run 1/2″ smaller), centered in the back wall, from 8′ 6″ to 11′ 6″ from the right corner. The top of its sill is 2′ 10″ above the top of the bottom plate, under a doubled 2×6 header. Tape the opening before the window goes in, sill first, then the sides, then the head. Drip cap goes over the door and window head casings.

What fits in an 8×20 lean-to shed

The front is the tall side, 8′ 7 1/8″ with plates. The back wall is 6′ 8″ and holds the window. Front to back the clear span inside is 7′ 5″, so check any shelf depth against that before you build it.

Only one leaf opens, 2′ 5 5/8″ wide, until you unbolt the fixed leaf for the full 5′ 0″. The astragal sticks out 3/4″ behind the fixed leaf, and the deck is 9 3/4″ above the gravel, so measure a mower or a wheelbarrow against both.

How the 8×20 lean-to roof is framed

A single-slope roof has no ridge, so it pushes nothing outward, and the hurricane ties hold it down in wind. Each rafter gets a hurricane tie on the inside face of both walls, and the two end rafters, where the side walls cover that spot, get framing angles instead. The end rafters also get nailed up through the sloped side plates every 16″, six nails per side.

For the 7′ 5″ clear span the plan uses 2×4 rafters at 16″ on center, in #2 spruce-pine-fir or Douglas fir-larch, assuming about 30 psf of ground snow. Snow loads and the span table differ from place to place, so check the rafter size with your local permit office before you buy.

Each rafter hooks over both walls with a birdsmouth: a 3 1/2″ level seat and a 7/8″ heel, about 24% of the rafter’s depth (the plan says never cut deeper than a third). Before cutting all of them, measure from the inside face of the front plates to the outside face of the back plates at both ends and in the middle. It should read 7′ 8 1/2″ every time, measured level across the shed and not along the slope. If the middle is off, push or pull the wall there and hold it with a temporary 2×4 across the plates until the rafters are in.

Then cut one pattern rafter from a straight 2×4, try it at both ends of the shed and cut the rest to match, 16 in all plus 2 fly rafters. The front birdsmouth is the one that gets cut backwards, and it has its own drawing. The fly rafters have no birdsmouth. They sit 2 1/2″ outside the end rafters on 2×4 lookout blocks and carry the 1×6 rake fascia.

Venting, felt and shingles

The blocking over both walls is ripped to 2 5/8″ tall and drilled with 1″ vent holes. Air comes in through a 1/4″ gap at the back soffit, rises up the rafter bays and leaves at the front. Staple the insect screen under the tails before the soffit strips go on.

At 3/12 the shingle makers ask for double felt: a 19″ starter strip, then 36″ courses each lapping 19″, with 4″ end laps. The drip edge goes under the felt at the low eave and over it on the rakes and the high front edge, where the water runs away. Then you lay 23 courses at 5″ exposure, about 183 shingles or 8 bundles including the starter, with the last course trimmed flush at the front and sealed with roofing cement.

Ladders and roof safety

With the high edge about 9′ 11″ off the ground, the tools list calls for a 20 ft extension ladder plus two 6 ft step ladders for the walls and rafters. Set the ladder 1 ft out for every 4 ft up, tie the top to a rafter or the fascia, and let it reach 3 ft or more past the edge. Look up before you raise a ladder or carry a sheet, and keep yourself, the ladder and the sheets at least 10 ft from any overhead power line.

On the roof, a 2×4 screwed down a foot above the eave gives you a foot stop, and nobody works up there alone. Don’t climb with a sheet in both hands: hand OSB up on its long edge to a helper on a step ladder. Shingle bundles weigh about 60 to 80 lb, so carry half a bundle at a time or ask the supplier if they’ll deliver them onto the roof.

Anchoring the shed

The 8×20 plan says an empty shed this size on loose skids slides at about 9 psf of wind (gusts near 50 mph) and tips at about 14 psf, so you anchor it once the roof is on and before you fill it. Check your local permit office for what your area asks.

You use 8 screw-in auger anchors, 30″ or longer and galvanized, each with a galvanized steel strap: four along each of the two outside skids, at 1′ 0″, 6′ 3″, 13′ 0″ and 19′ 0″ from the left end, and each at least 3″ clear of a splice scab. The anchor goes in tight against the outside face of the skid until its eye sits about 1″ above the ground. The strap runs up the skid’s outer face and onto the rim joist, below the siding, and takes 1 1/2″ structural screws, 4 into the skid and 2 into the rim, 48 screws in all. Firm, undisturbed soil holds best; in sand or loose fill the plan says to use longer anchors.

Free 8×20 lean to shed plans PDF vs the full plan

The free PDF is 7 pages. It walks the five stages (site, floor, walls, roof, trim) with 3D views of the same model, so you can see the drawing style and the finished shed before you pay. The full 45-page plan adds the shopping list, the cut list, the cutting plan, every wall drawn stud by stud with a position table, every sloped stud length, the rafter marks, piece maps for the deck, siding and roof sheathing, the door build and pro tips on most steps. It runs 18 build steps from ground prep to paint, with a checklist page to tick off. Every number comes from one 3D model that passed 87 automatic checks, such as plates plus studs adding up to the wall height.

Before you build an 8×20 lean-to shed

Rules for sheds come from your town, and from your HOA if you have one. Size, height, distance to the property line and whether you need a permit at all vary, so check your local permit office before you spend money on lumber. Ask the same office about snow and wind, since heavy snow or high wind can call for closer rafters or bigger rafters. This is common small-shed framing, not an engineered design, and the disclaimer says so on page 2.

After the build, keep 6″ or more between the siding and the soil or mulch, and keep gutters or drip edges clear. Each spring, check the roof for lifted shingles, re-caulk the trim joints, touch up the paint and make sure the skids are still level and dry.

Tools the plan lists

The plan assumes a circular saw with a rip guide, a drill/driver and a framing hammer. On top of those come a miter saw for the door braces and trim, a reciprocating saw or oscillating tool for the flush cuts in the door and window openings, two 24″ bar clamps for marking the rims together, a 3 lb sledge for the brace stakes, and a shovel, rake and hand tamper for the gravel.

Related plans

• Same 8 ft depth, 4 ft shorter: the 8×16 lean-to shed plan.
• Same footprint with a two-sided gable roof: the 8×20 gable shed plan.
• Every size on the lean-to shed plans page.