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Building a Subfloor

Project Overview

Building a Subfloor

Most shed kits don't come with a floor, so you have to decide what you want and build it yourself. If you're building on a concrete slab, a subfloor is optional: The concrete is its own subfloor. If you choose to build a subfloor over a concrete pad, anchor it to the slab with angle irons, lag screws, and anchor shields. Build a subfloor made of 3/4-inch exterior grade plywood on a frame of pressure treated 2x6s. Strengthen the corners with corner brackets and anchor them to the foundation.

6 Steps

  1. Cut the joists
  2. Build and square the frame
  3. Attach metal hangers
  4. Lay out the joists
  5. Cut the joists
  1. Lay the subfloor
Show all steps »
Cut the joists

Step 1

Cut the joists

Cut the 2x6s to make the four sides of the platform. They're called end and header joists. The headers are the ones that all the other joists nail into. Cut the end joists 3 inches shorter than the frame dimension to account for the thickness of header joists.

Build and square the frame

Step 2

Build and square the frame

Nail the end and header joists together with 10d (3 inch) common nails. Set the frame in place on the foundation. Check for square by measuring across opposite corners. Adjust the frame as needed until the two diagonal distances are equal.

Attach metal hangers

Step 3

Attach metal hangers

Nail a corner bracket at each corner of the frame to reinforce the joint. Attach the frame to the skids with hurricane/seismic ties. Recheck the corner for square.

Lay out the joists
Lay out the joists

Step 4

Lay out the joists

Mark joist positions every 16 inches on the opposing header joists. Extend the lines down the inside face of the header joists with a combination square. Centre a joist hanger at each mark. Drive nails through the flange on only one side of each hanger so you can insert the joists easily.

Cut the joists

Step 5

Cut the joists

Cut the 2x6 joists to length and set them in the hangers. Press each hanger closed, nail the other flange to the header joist, then nail the hanger to the sides of the joist.

Lay the subfloor
Lay the subfloor

Step 6

Lay the subfloor

Lay 3/4-inch exterior-grade plywood on the joists. Trim panel so joints are at the centre of joists, but stagger the joints so no joint runs into another joint. Leave a gap of 1/2-inch between edges to keep the panels from buckling. Fasten the panels to the joists with 8d (2 1/2-inch) nails or #8-2 1/2-inch deck screws. Space the fasteners every 6 inches along the edges of the panel and 12 inches else where.

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Project Details

Skill Level: Intermediate

Time: 8 hours

Before you start, read this »

Due to differing conditions, tools, and individual skills, The Home Depot® assumes no responsibility for any damages, injuries suffered, or losses incurred as a result of attempting to replicate any of the home improvement ideas portrayed in this website Before beginning any home improvement project, review it thoroughly to ensure you or your contractor can finish the project and if any doubts or questions remain, consult local experts or authorities. Because codes and regulations vary greatly, you always should check with authorities to ensure that your project complies with all applicable local codes and regulations. Always read and observe all of the safety precautions provided by any tool or equipment manufacturer, and follow all accepted safety procedures.


  • 2x6s
  • 8d (2½ inch) nails or #8 2½ inch deck screws
  • 10d (3 inch) nails
  • Corner Brackets
  • Joist Hangers
  • ¾ inch Exterior-grade Plywood
  • Pencil
  • Hurricane/seismic Ties

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