12x20 Lean-To Shed Material List: Lumber, Sheets, Hardware

Last updated October 18, 2026

A 12×20 lean-to shed material list on skids comes to 67 framing 2x4s, 23 plain 2x6s (18 are 14 ft rafter stock), 21 treated 2x6s and 8 treated 4x4s. Sheets: 8 floor plywood, 11 OSB, 18 T1-11, 1 soffit plywood; 10 shingle bundles. Assumes an 80 in back wall, 115 1/8 in front wall and 3/12 roof.

Many yards do not stock 20 ft boards, so every 20 ft run on this list (skids, rims, front and back plates, eave fascia) is spliced from two boards. Each side wall also has 10 studs of 10 different lengths under a sloped plate. This list is for a freestanding shed with a shingle roof. For the house-wall version, see building a lean-to shed against a house.

What this 12×20 lean-to list assumes

This list is for a shed 12 ft deep and 20 ft wide, with 240 sq ft of floor. The roof slopes front to back, so the 20 ft front wall with the door is the tall one.

• Walls: the back (low) wall is 80 in tall and the front (high) wall is 115 1/8 in, both including the bottom plate and double top plate. Back studs are 6′ 3 1/2″ and front studs 9′ 2 5/8″.
• Roof: 3/12 pitch (about 14 degrees), 2×6 rafters with a birdsmouth on both walls, 8 in overhangs front and back, 4 in rakes. The roof is 248 in long by about 165 in down the slope, roughly 284 sq ft.
• Height: about 11 ft 1 in tall overall at the high front edge, measured from the bottom of the skids.
• Spacing: studs, floor joists and rafters at 16 in on center.
• Floor: four pressure-treated 4×4 skids on a crushed stone pad, 2×6 joists across the 12 ft depth, 3/4 in tongue and groove plywood.
• Loads: the 2×6 rafters span 137 in. The span check behind this list allows 143 in for SPF #2 at 16 in and 30 psf ground snow, but only 134 in for Southern pine #2, so buy SPF or go up to 2×8 in Southern pine. Many areas design for more than 30 psf, so check your local permit office for your snow load before you buy rafter stock.
• Openings: a 60 in double door in the front wall and one 36 x 36 in window in the back wall.

Shopping list by stage: the full 12×20 lean-to shed material list

Lumber sizes are nominal. A 2×4 measures about 1 1/2 x 3 1/2 in and a 2×6 about 1 1/2 x 5 1/2 in, as the American Wood Council explains. Check the grade stamp on plywood and OSB; the APA trademark guide shows how to read it.

Floor

Item	Qty	Used for
Pressure-treated 4×4 x 12 ft, ground-contact rated	4	Skids, long piece
Pressure-treated 4×4 x 8 ft, ground-contact rated	4	Skids, short piece (each skid is 12 ft + 8 ft)
Pressure-treated 2×4 x 14 ft	2	8 splice scabs, 3 ft each, both sides of each skid joint
Pressure-treated 2×6 x 12 ft, ground-contact rated	19	17 floor joists (one doubled at the rim joint) and part of each rim
Pressure-treated 2×6 x 10 ft, ground-contact rated	2	The other part of each 20 ft rim joist
3/4 in T&G plywood, 4×8 sheet	8	Floor decking
1×4 x 8 ft	part of 6	3 decking filler strips, ripped to 1 1/2 in
Crushed stone 3/4 in, loose	4.6 cu yd	Gravel pad
Deck screws 2 in (or 6d ring-shank nails)	6 lb	Decking

Walls

Item	Qty	Used for
2×4 x 8 ft	17	Shorter side-wall studs, back plates and caps, part of the front cap, back sill and lower cripples, lookout blocks
2×4 x 10 ft	28	Front wall studs, taller side-wall studs, front cripples
2×4 x 12 ft	8	Side-wall plates, sloped top plates, back plates and caps, back window trimmers
2×4 x 14 ft	14	Back wall studs (two per board), front plates and cap, front door trimmers
2×8 x 12 ft	1	Door header
2×6 x 8 ft	2	Window header, some rafter blocking
Strap ties (twist straps)	4	Lean-to wall corners
Temporary braces 2×4 x 12 ft	15	Wall bracing, reused later
2×4 x 8 ft for stakes and cleats	3 + 2	10 stakes 24 in and 10 deck cleats 12 in

The two header filler strips of 1/2 in plywood are ripped from the soffit sheet, so buy that sheet with the wall lumber. The 67 framing 2x4s plus 15 braces and 5 stake and cleat boards make 87 untreated 2x4s on the truck, and 2 treated 2x4s go with the floor.

Roof

Item	Qty	Used for
2×6 x 14 ft, SPF #2 or better (not Southern pine #2)	18	16 rafters and 2 fly rafters
2×6 x 12 ft	3	Blocking between rafters
Hurricane ties, H2.5A type or equal	32	Rafter to plate, both walls
7/16 in OSB, 4×8 sheet	11	Roof sheathing
15 lb felt, 400 sq ft roll	2	Underlayment, laid double below 4/12
3-tab shingles, 26 per bundle	10 bundles	Roof and starter course
Drip edge, 10 ft	8	Eaves and rakes
Roofing nails 1 1/4 in galvanized	10 lb	Shingles
Roofing cap nails 1 in	2 lb	Felt
Roofing cement, 10 oz tube	2	Roofing

Siding and trim

Item	Qty	Used for
5/8 in T1-11, 4×10 sheet	5	Front (high) wall
5/8 in T1-11, 4×8 sheet	5	Back (low) wall
5/8 in T1-11, 4×10 / 4×9 / 4×8 sheet	2 / 2 / 2	Sloped side walls (4×10 cut down if no 4×9)
5/8 in T1-11, 4×8 sheet	2	Door leaves (one per leaf)
1/2 in plywood, 4×8 sheet	1	Eave soffit and header fillers
1×8 x 16 ft	2	Rake fascia
1×8 x 12 ft and 1×8 x 10 ft	2 each	Eave fascia (one of each per eave)
1×4 x 14 ft	6	Back corner trim, door casing sides, stiles, Z braces
1×4 x 12 ft	1	Door rails
1×4 x 10 ft	4	Front corner trim
1×4 x 8 ft	6	Door head casing, window casing, decking filler strips
1×2 x 8 ft	2	Door stop and astragal
Drip cap, 10 ft	1	Over the door and window head casings
Insect screen, 2 ft x 25 ft	1 roll	Gaps at the eaves and soffit
Exterior paint and primer in one	6 gal	Two coats, about 695 sq ft each
Exterior caulk	3 tubes	Trim

Hardware and window

Item	Qty
Framing nails 3 1/2 in (16d), hot-dip galvanized	30 lb
Siding nails 2 1/2 in (8d), hot-dip galvanized	20 lb
Sheathing nails 2 1/2 in (8d) for OSB	10 lb
Connector nails 1 1/2 in for ties and straps	3 lb
Construction adhesive, 10 oz tube	11
T-strap door hinges	6
Door handle and latch set	1
Barrel bolts for the fixed leaf	2
Exterior screws 1 1/4 in (door frame to T1-11)	1 lb
Exterior screws 2 1/2 in (hinge straps into framing)	1 box
Prefabricated window, 36 x 36 in rough opening	1
Flashing tape 4 in	1 roll
Wood shims	1 bundle

Cut list highlights

Most of the 12×20 lean-to cut list is square cuts: 17 front studs at 9′ 2 5/8″, 18 back studs at 6′ 3 1/2″ and 17 floor joists at 11′ 9″. The parts below carry angles, splices or a different length every time, so one layout error repeats down the wall.

Part	Lumber	Cut length	Qty
Skid (spliced)	PT 4×4	20′ 0″	4
Rim joist (spliced)	PT 2×6	20′ 0″	2
Skid splice scab	PT 2×4	3′ 0″	8
Front and back wall plates and caps (spliced)	2×4	20′ 0″	3 per wall
Rafter (board length)	2×6	13′ 10 1/4″	16
Fly rafter (rake)	2×6	13′ 10 1/4″	2
Side wall sloped top plate	2×4	11′ 9 1/8″	2
Side wall bottom plate	2×4	11′ 4 7/8″	2
Left wall studs	2×4	6′ 5 3/8″ to 9′ 3 1/4″	10, all different
Right wall studs	2×4	9′ 3 1/4″ down to 6′ 5 3/8″	10, all different
Door header (2×8 doubled + 1/2 ply)	2×8	5′ 3″	2
Door trimmer	2×4	6′ 4 1/2″	2
Cripple over the door	2×4	2′ 2 7/8″	4
Window header (2×6 doubled + 1/2 ply)	2×6	3′ 3″	2
Window trimmer	2×4	5′ 10″	2
Blocking between rafters	2×6	1′ 1 3/4″ and 1′ 2 1/2″	4 and 26
Lookout block (rake overhang)	2×4	2 1/2″	16
Eave fascia (spliced)	1×8	20′ 8″	2
Rake fascia (tip to tip)	1×8	14′ 0 1/4″	2

Splices. No 20 ft boards appear on the list. Each skid is a 12 ft and an 8 ft 4×4 butted end to end, with a 3 ft treated 2×4 scab on both sides of the joint. Each rim joist is a 12 ft and a 10 ft 2×6 cut to 20′ 0″, with an extra floor joist at the rim joint so both rim ends nail into it. The back plates and cap come from a 12 ft and an 8 ft 2×4, exactly 20 ft with no trim margin, so pick boards with square factory ends. Keep the plate joints away from the skid joints so the floor and walls do not share a weak spot.

Rafters. The 13′ 10 1/4″ figure is the board each rafter needs, measured corner to corner, including both 8 in overhangs. Mark the plumb cuts at each end at 3 on the common scale of a speed square (about 14 degrees). Each rafter gets two birdsmouths, one on each wall, with a 3 1/2 in seat that notches under 1 in into the 2×6. That stays well under a third of the rafter depth. Test a pattern rafter on both walls before tracing the rest.

Side wall studs. Each side wall has 10 studs under a sloped top plate, and both walls use the same 10 lengths. Every length is the long point, from the top of the bottom plate to the underside of the sloped plate. From the back corner they run 6′ 5 3/8″, 6′ 8 1/4″, 7′ 0 1/4″, 7′ 4 1/4″, 7′ 8 1/4″, 8′ 0 1/4″, 8′ 4 1/4″, 8′ 8 1/4″, 9′ 0 1/4″ and 9′ 3 1/4″. The right wall’s list starts at the front corner, so it reads the same lengths in reverse.

The tops are cut at the roof angle (3 on the common scale of a speed square, about 14 degrees). The 16 in layout starts from a different corner on each wall, so label each stud with its wall and position.

Headers. The 60 in door gets a doubled 2×8 header with a 1/2 in plywood filler on 6′ 4 1/2″ trimmers. The front wall is tall, so the four cripples above the header are 2′ 2 7/8″, much longer than on a gable shed. The back window header is a doubled 2×6 on 5′ 10″ trimmers and fills the space up to the plates, so there are no cripples above it. Below the window go a 3′ 0″ sill and two 2′ 8 1/2″ cripples.

Gable vs lean-to: what changes

The same 12×20 footprint run as a gable at 6/12 (94 1/2 in walls, ridge along the 20 ft side) uses the same floor; the walls and roof are where the lists split. Our 12×20 shed material list covers the gable version in full.

Item	Lean-to (3/12)	Gable (6/12)
Rafters	16 2×6 at 13′ 10 1/4″ + 2 fly	32 2×4 at 7′ 6 3/8″ + 4 fly
Ridge board	None	2×6, 20′ 8″, from a 12 ft and a 10 ft board
Rafter ties and collar ties	None (no ridge, no outward thrust)	14 rafter ties + 7 collar ties
Wall studs	9′ 2 5/8″ front, 6′ 3 1/2″ back, stepped sides	7′ 6″ on all four walls, plus 18 short gable-end studs
2×4 framing boards (plus 15 braces and 5 stake and cleat boards in both)	67	147, plus a 12 ft temporary ridge post
2×6 boards (not treated)	23	4
T1-11 sheets	18: seven 4×10, two 4×9, nine 4×8	20, all 4×8
Roof OSB sheets	11	11
Shingle bundles	10	12 (incl. ridge cap)
Felt	2 rolls, laid double	1 roll, single
Fascia	1×8	1×6
Soffit plywood	1 sheet	2 sheets
Framing nails	30 lb	43 lb
Windows	1	2
Extra hardware	4 twist straps	2 gable vents, 3 Z-flashing, a temporary ridge post
Floor (skids, joists, decking)	8 PT 4×4, 21 PT 2×6, 8 sheets	8 PT 4×4, 21 PT 2×6, 8 sheets

The lean-to needs 80 fewer 2x4s and no ridge, ties or gable triangles, but it buys 19 more plain 2x6s, a second roll of felt, and 9 of its 18 siding sheets are 4×10 or 4×9. A lean-to sends all its roof water off the back edge, so keep that side clear of fences and paths.

Where the waste goes

Offcuts by part:

• Rafters: 13′ 10 1/4″ from a 14 ft 2×6 leaves only about 1 3/4 in. There is no room for a split end, so pick straight boards and consider one spare 14 ft 2×6.
• Back studs: two 6′ 3 1/2″ studs come out of each 14 ft 2×4, leaving about 17 in.
• Front studs: 9′ 2 5/8″ from a 10 ft board leaves about 9 3/8 in each, good only for small blocks.
• Side studs: the five shorter studs on each wall come from 8 ft boards and the five taller ones from 10 ft boards. The 8′ 0 1/4″ stud is just over 8 ft, which is why it needs a 10 ft board.
• Sloped top plates: 11′ 9 1/8″ from a 12 ft board leaves about 2 7/8 in.
• Floor joists: 11′ 9″ from a 12 ft board leaves 3 in for squaring the ends.
• Skid scabs: four 3 ft scabs come from each 14 ft treated 2×4, leaving about 2 ft.
• Eave fascia: each 20′ 8″ eave fascia is spliced from a 12 ft and a 10 ft 1×8, leaving about 16 in. Land the joint on a rafter tail. Each 14′ 0 1/4″ rake fascia leaves about 2 ft of a 16 ft board.
• No spares: the counts are exact. Add a few 2×4 x 8 ft if you expect to reject warped or split boards.

The longest boards on this list are 16 ft (rake fascia) and 14 ft (rafters, back studs, front plates).

Common mistakes

• Buying 4×8 siding for the front wall. The front wall is 115 1/8 in tall, close to 10 ft, so the front and part of each side take 4×10 or 4×9 T1-11. Many yards stock 4×10 but not 4×9, so call ahead; a 4×10 cut down covers a 4×9 spot.
• Splicing skids anywhere. Set each skid joint on tamped gravel with both scabs nailed on before the floor goes down, and keep plate joints away from it.
• Measuring side studs off the wrong end. The two side walls read the same lengths from opposite corners, so a stud cut for one wall lands in the wrong spot on the other.
• Single felt at 3/12. The list doubles the felt below 4/12, which is why it has 2 rolls. Read the minimum slope on the shingle wrapper, and check your local permit office for the underlayment rule in your area.
• One birdsmouth instead of two. Each rafter bears on both walls, so it needs a seat at the front and at the back. Mark both from the pattern rafter.
• Raising the front wall alone. A 20 ft wall with 9 ft studs and a doubled 2×8 header is heavy and catches wind. That is why the list carries 15 temporary braces.
• Untreated wood near the ground. Skids, rims, joists and scabs are pressure treated and sit within a few inches of the gravel, so buy all of them rated for ground contact. The USDA Wood Handbook explains why wet, untreated wood decays. Use hot-dip galvanized nails and treated-lumber rated screws in treated wood.

Setbacks, height limits, ground anchors and whether a 240 sq ft shed needs a permit vary by town, so check your local permit office before you order. For how to read any list like this one, see our shed material list guide. For the base under the skids, see shed foundation options, and for the build itself, how to build a lean-to shed. For other sizes, try the shed material calculator.

Get the full plan

We do not sell a 12×20 lean-to plan yet. For a single-slope roof on the same 12 ft depth, the 12×18 lean-to shed plan is the nearest size down and the 12×24 lean-to shed plan the nearest size up. The 14×20 lean-to shed plan keeps the 20 ft width and adds 2 ft of depth.

For this exact footprint, the 12×20 gable shed plan and the 12×20 hip roof shed plan are 3DSHEDPLANS PDFs with 3D drawings, cut details and their own printable material list. Download the free 12×24 lean-to preview PDF to see the format, or compare every size on the lean-to shed plans and shed plans pages.

Frequently asked questions

What is on the material list for a 12×20 lean-to shed?

For a 12×20 lean-to on skids with an 80 in back wall and a 3/12 roof: 67 2×4 framing boards, 23 plain 2x6s (18 of them 14 ft rafter stock), 21 treated 2x6s, 8 treated 4x4s for the spliced skids, 2 treated 2x4s for splice scabs and one 2×8 for the door header.

How many sheets of plywood, OSB and T1-11 for a 12×20 lean-to shed?

8 sheets of 3/4 in tongue and groove plywood for the floor, 11 sheets of 7/16 in OSB for the roof, 18 sheets of 5/8 in T1-11 (seven 4×10, two 4×9, nine 4×8, including 2 for the door leaves) and 1 sheet of 1/2 in plywood for the soffit and header fillers.

What size rafters does a 12×20 lean-to shed need?

16 2×6 rafters at 16 in on center plus 2 fly rafters, cut from 14 ft boards to 13' 10 1/4". They span 137 in, under the 143 in allowed for SPF #2 at 30 psf ground snow but over the 134 in for Southern pine #2, which needs 2×8. Check your local permit office for snow load.

How many bundles of shingles does a 12×20 lean-to roof take?

10 bundles of 3-tab shingles, including the starter course, for a 3/12 roof of about 284 sq ft with 8 in eaves and 4 in rakes. The felt goes on double below 4/12, so the list has 2 rolls of 15 lb felt.

Are there 12×20 lean-to shed plans with a material list?

We do not sell a 12×20 lean-to plan yet, so this page is the list. The 3DSHEDPLANS 12×18 and 12×24 lean-to plans and the 12×20 gable plan are PDFs with 3D drawings and their own printable material list.