How to Build a Shed Floor on Skids, Step by Step

Here is how to build a shed floor: set pressure-treated skids level on a gravel pad, mark the joist layout on two 2×6 rim joists, nail the joists between them at 16 in on center, square the frame by its diagonals, fasten it to the skids, then glue and screw 3/4 in tongue and groove plywood on top.

Every 3DSHEDPLANS shed plan is drawn on this floor. The worked numbers come from a 10×12 shed (10 ft deep, 12 ft wide). The base under the skids is covered in shed foundation options.

How to build a shed floor: parts, lumber and tools

A skid floor has four parts, from the ground up:

• Skids: 4×4 pressure-treated runners that run the long way of the shed. Skids also let a shed be dragged to a new spot later.
• Rim joists (band): two 2×6 boards along the long sides that hold the joist ends.
• Floor joists: 2×6 boards that span the short way, between the rims, every 16 in.
• Decking: 4×8 sheets of 3/4 in tongue and groove plywood.

Tools: circular saw, sawhorses, speed square, tape, chalk line, two bar clamps, 4 ft level, an 8 ft straight board, nail gun or hammer, drill driver, caulk gun, a short sledge, safety glasses, hearing protection and a helper. Wear gloves and a dust mask when cutting treated lumber, and never burn the offcuts.

Lumber and fasteners: buy pressure-treated lumber for the skids, rims and joists, and read the end tag. The American Wood Protection Association’s treated wood guide points ground-contact treatment (UC4A) at wood less than 6 in above the ground or hard to replace later. On 4×4 skids the rims and joists are only 3 1/2 in up, so all three should be rated for ground contact. Use hot-dip galvanized or stainless fasteners rated for treated lumber.

How many skids, joists and sheets does a shed floor need?

This is what our 3DSHEDPLANS plans list for the floor of five shed sizes, with joists at 16 in on center. Joist lengths are cut lengths: buy 8, 8, 10, 12 and 14 ft boards.

Skid spacing is center to center, with the outer skids flush with the outside of the frame. Joists are cut 3 in shorter than the floor depth to fit between the two 1 1/2 in rims, and the counts include a joist at each end. The 10×12 and 14×24 also need a row of flat 2×4 blocks under the last decking seam (Step 5); the other three need none.

On the 24 ft floor the skids and rims are spliced from 16 ft and shorter boards. Each skid joint sits under a joist with a 3 ft treated 2×4 scab on both sides, joints on neighboring skids at least 4 ft apart, and each rim joint lands on a second joist nailed beside a layout joist (the + 1). The shed material list guide turns a list like this into an order, and what a shed costs to build gives rough price ranges.

Step 1: Set and level the skids

Set the outer skids where the frame edges will be and space the rest at the table’s center-to-center number, measuring at both ends so they run parallel. Sight down each one and turn it crown up, so the slight curve along the board faces the sky.

Check the skids with the level on the 8 ft straight board laid across them: they must be level with each other, not only each one on its own. Fix a low skid by adding or tamping stone under it, not by stacking shims, which crush and shift.

Step 2: Mark the joist layout on both rims

Cut the two rims to the shed’s full width (144 in on the 10×12), clamp them side by side with the ends flush, and mark both at once.

Mark one joist flush at each end. Then hook the tape on the end and mark lines at 15 1/4 in, 31 1/4 in, 47 1/4 in and every 16 in after that, and put an X on the far side of each line. That puts each joist’s center on a 16 in mark, so every 8 ft sheet end lands on the middle of a joist.

Step 3: Build the frame and nail in the joists

Cut the joists to the floor depth minus 3 in: 117 in (9 ft 9 in) on the 10×12. Set each one crown up. Brush an end-cut wood preservative on every cut end of treated lumber.

Stand the rims on edge, set each joist on its X, and nail through the rim into the joist end with three 3 1/2 in (16d) galvanized nails, keeping the tops flush. The joist ends rest on the outer skids, so the end nails only hold the frame together and joist hangers are not needed.

Step 4: Square the frame and fasten it to the skids

Check that both rims and both end joists match in length, then measure both diagonals, corner to corner: on a 10×12 floor both should read about 187 7/16 in. Push the two corners of the longer diagonal toward each other until they match within 1/8 in.

Set the frame on the skids with the rims flush with the outside of the outer skids, and measure the diagonals again, since moving it can rack it. Toenail one rim to its skid, rack the frame until the diagonals match, then toenail every joist to every skid it crosses: two 3 1/2 in galvanized nails per crossing, or 4 in structural screws. If you will anchor the shed, strap ground anchors to the skids or rim now, while you can reach them, and check your local permit office for what your area expects.

Step 5: Lay the tongue and groove plywood

Lay the sheets with the long side across the joists, starting at the rim corner where you hooked the tape for the layout. On the first row, the groove edge faces out along the rim and the tongue faces the next row.

• Glue: run a bead of subfloor adhesive along every joist under each sheet and a thin bead in the groove, one or two sheets at a time so it does not skin over.
• Gaps: leave about 1/8 in at sheet ends and edges so the panels can swell. APA’s builder tip on panel spacing suggests a 10d box nail as a spacer.
• Fastening: 2 in deck screws, 6 in apart along supported edges (sheet ends on joists, the rim and any blocking) and 12 in apart along the joists in between, about 3/8 in in from the edges. APA’s Sturd-I-Floor details show the panel layout and support rules.
• Stagger: start the second row with a half sheet, so the end joints do not line up from row to row.
• Seating: fit each sheet’s groove onto the tongue before it and tap it home with a sledge against a plywood offcut that still has its groove, so the exposed tongue is not crushed.

On a floor that is not a multiple of 4 ft deep, like the 10×12, the last row is a 24 in strip, and one sheet ripped down the middle gives one strip with the groove and one with the tongue. Only the groove strip can lock onto the row before.

So nail flat 2×4 blocks in every joist bay under that seam, flush with the joist tops (9 blocks from two 8 ft 2x4s on the 10×12), and screw both sheet edges to them. The ripped edges land on the rim. A 12 ft deep floor is three full rows and needs no blocking.

Step 6: Protect the floor until the walls go up

Seal any cut plywood edges with primer or paint, and cover the floor with a tarp if rain is coming before the roof is on. Snap chalk lines 3 1/2 in in from each edge to mark where the wall bottom plates will sit.

Skids or blocks, insulation and critters

On a slope, a floor on piers or blocks uses beams in place of skids, and the joists then span farther, so size them with the American Wood Council span calculator. Where frost heaves the ground, skids on gravel float with it; piers resist heave only when they go below the frost line, so check your local permit office for that depth. Shed foundation options compares those bases.

To insulate the floor, fit rigid foam board between the joists before the decking goes on, held up on cleats nailed to the joist sides, and tape or foam the seams. To keep animals out of the gap under the floor, staple galvanized hardware cloth around the outside of the skids and bury its bottom edge a few inches in the gravel; without it, mice nest in floor foam. If a mower will roll in, plan a ramp at the door and keep a joist or blocking right under the door threshold.

Common mistakes when building a shed floor

• Laying out from different ends. The joists no longer line up across the frame, and the sheet ends miss the joists.
• Skids on bare soil. They stay wet and rot from below, and the floor settles unevenly.
• Sheet ends off the joist center. An end with only 1/4 in of bearing pulls loose; trim the sheet to land on the middle.
• Under-building for heavy loads. For a riding mower or a safe, add a skid under the wheel path or go to joists at 12 in on center (the table assumes 16 in).

Shed rules vary by town, so check your local permit office before you build.

What we checked: part counts, skid spacing and diagonals come from the 3DSHEDPLANS plan generator, with the diagonals recomputed from the floor size; the floor steps and fastener schedule match the floor pages in our plan PDFs; panel gaps from APA; treated wood use categories from AWPA; joist span checks from the American Wood Council.

Plans that fit

Each 3DSHEDPLANS plan is a $19.99 PDF with the full material list, a floor framing plan with the joist marks and diagonals for that size, and 3D step-by-step images.

• 10×12 gable shed plan: the size in the worked example. See the floor pages first in the free 10×12 gable shed plan preview.
• The other sizes in the table: the 8×8 gable shed plan, the 8×10 gable shed plan, the 12×16 gable shed plan and the 14×24 gable shed plan.

The same floor sits under our lean-to shed plans and hip roof shed plans. Once the floor is down, the next stages are how to build a shed roof and how many 2x4s to build a shed for the wall framing.