How To Build a Shed Floor [Step-by-Step Guide]

A shed is a necessity for any backyard where you want to maximize your storage. Regardless of whether  you are building it yourself or having a pre-built shed delivered, you will need to build a solid shed floor where your shed will ultimately stand.

I’m sure you’re wondering how to build a shed floor? Here’s the process:

• Measure and cut rim joist and floor joist boards from 2×6 treated lumber
• Set rim joists on shed foundation
• Nail outer floor joists to rim boards
• Attach the joist hangers to rim joists
• Install the rest of floor joists
• Make sure the floor framing is square
• Install 3/4 inch plywood

If this is your first time building a shed floor, it is a relatively simple process. You don’t need to be the world’s best carpenter or even have an abundance of tools to make a great subfloor for your shed. After reading this guide, you will have all the necessary information to build a solid shed floor that will last the life of your shed.

How To Build a Shed Floor – Step by Step Guide

Materials

• 2 x 6 pressure treated lumber
• ¾ inch pressure treated plywood
• Joist hangers
• Fasteners – 3” framing nails 16d and 3” exterior grade Simpson screws
• 2” wood screws (for plywood)

Recommended tools (available on Amazon)

• Level
• Chalk Line
• Tape Measure
• Speed Square
• Circular Saw
• Nail Gun
• Palm Nailer

Step 1: Lay Out Deck Blocks and Level the Area

I’ve found that most sheds can easily sit on deck blocks instead of pouring a concrete slab foundation. They are much cheaper and more user-friendly, especially if you are new to shed building.

Lay out your deck blocks and level the ground around them. They should be placed an equal distance apart, every 4 to 6 feet, so there is stability on the ends and in the middle.

An easy way to do this is to take your 2×6 and lay it in the grooves of the deck blocks. Tamp down or dig the ground so that you have a nice level surface to support the frame of your floor. Don’t worry about nailing anything together just yet; you can mock up your frame to get the blocks level.

Step 2: Build the Outer Frame

Some people will say that you can build the frame with 2 x 4 lumber, but I prefer to use 2 x 6 pressure treated lumber instead. The added stability from a 2 x 6 over a 2 x 4 will be noticeable, especially if you are looking to store heavier items.

I’m not going to give you exact measurements for the cuts because every shed is different and you should have the shed dimensions before buying the materials for the shed floor.

Take your measurements for all four sides and cut the lumber accordingly. I like to use a speed square to mark the cuts and as a guide for a circular saw. You can also use a miter saw or chop saw if you have one. Don’t forget to seal all end grain cuts with wood preservative.

Make sure that your measurements are exact. There’s the old saying of measure twice and cut once. You can’t be too precise here. This is the time to tap into that OCD that everyone tells you is a bad thing.

Once you have your cuts made, nail the frame together with the 3 inch 16d framing nails. Make sure to put three nails to join every board, one on top, one in the middle, and one on the bottom. The four planks should form a box at this point.

 

Step 3: Check if Your Floor Frame is Square

This is an often overlooked step, especially by beginners. You need to make sure that the frame you built is square.

This is a relatively simple process. Just take a tape measure and measure diagonally from one corner to the other. The measurement should be the same. If it’s not, try a hammer at the longer corner to make it square, otherwise, you may need to shift a deck block a bit.

Usually, it will only be off by a ¼ inch or so, and it won’t take much effort. Remember you’re working with lumber, so you don’t have to be too gentle. Measure again and repeat the process until you have a square frame.

Step 4: Add the Joists

I like to put the first joist right in the middle of the frame. If your frame is square (from the step above), then you should be able to cut each joist the same length.

Measure out your joists and like above, use the speed square to help make your cuts with the circular saw.

Once you have all your joists cut, mock up the frame by placing the joists inside the frame. You want your joists to sit 12 inches on center. Some people will tell you 16 inches is ok, but I like to make my shed floor extra strong. It won’t cost you much more in the long run.

Mark the 12-inch increments along the length of the frame. When I do this, I like to make sure that my measurements on both sides are exact. Mark where the center of each joist should sit on the top of the wood frame. This will make it very easy once you hang the joists to the frame.

Attach the joist hangers to the frame using the Simpson screws. I like to use a cut-off block from a joist to align each so it is centered on my mark and flush with the top.

It is essential in this step to make sure the joists sit flush with the top of the frame. This is where it is nice to have someone helping you by holding the cut-off block and hanger.

Drop the joists into the hangers, you may need to tap them with a hammer. Use the 3” nails to attach the hangers to the joists. Angle the nails so the go through the joist and into the frame.  

If your storage shed is going to be larger, then you will want to put in a middle support beam that goes the opposite direction of the way your joists are hanging. Although a 2×6 can span 11’-10”, a span 8-feet or longer should have a center support beam.

Once all the joists are hung, cut and insert 2×6 blocks using 3” nails at 4-foot and 8-foot distances from the outside edge of your frame. These will prevent the joists from twisting and also support the edge of your plywood flooring. You should now have a solid frame.

At this point you should think about anchoring your floor frame.

Step 5: Lay the Plywood

If your shed is larger than 4’ x 8’, it’s a good idea to offset the seams on the plywood to add to the stability of the shed floor. I like to make my cuts and lay out all the plywood to get it even on the frame before I start screwing it down. The plywood is milled square, so it will also help ensure your frame is square too.

Once the 3/4 inch treated plywood is laid where you want it, I always snap a chalk line to identify the joists. This will make screwing down the plywood much easier and you’ll avoid missing the center of the joist.

Wood screws work better than nails here. Why? It’s simple. Screws will give you a more secure floor, and the screws won’t back out of the wood like nails have a tendency to do.

Another benefit to wood screws is that they help to prevent squeaks and bumps on the floor. I like to place the screws about 8 inches apart, to give a uniform look and for stability.

Where two pieces of plywood butt up against each other, I put two screws on each piece of plywood, right next to each other to prevent any lifting.

At this point, the floor of your shed is finished and ready for the shed to be installed. Also, you can choose to stain or treat the floor with some sort of sealer, or leave it unfinished.

Conclusion

Building a shed floor is a relatively straightforward process that almost anyone can do. You need to be patient with the process. Remember, that being slow and methodical with your measurements (measure twice, cut once) and cuts is better than trying to get it thrown together quickly.

Your ultimate goal should be to make your shed floor last for the lifetime of the shed. A well-built floor will make all the difference when it is time to install the shed. Good luck, I know you’ll do just fine.