Project: Building a Shed - Part 2 - Subfloor

Published: 2022-1-13 | Tags: building woodworking

Part 2 - Subfloor

Fusion 360 Model

In the previous post, I talked about building a concrete pier foundation. Once I had completed the foundation, it was time to construct the subfloor.

Here are some resources that I found helpful for this part:

Step 1 - Placing the Runners

The Runners are 6x6 posts that are 16 feet long (the length of the shed). They rest on the 3 rows of concrete piers and support the weight of the entire shed.

Shed Runners

In order to join the runners to the concrete piers I used Simpson Strong-Tie post bases that I had previously attached to the concrete piers with a wet-set bolt.


The hole that secures the post base to the concrete pier is a little wider than it needs to be. This is so that you can adjust the post base back and forth a little bit. I used this to make sure the runners were perfectly parallel to each other. The reason that this is helpful is that it is very difficult to get the concrete piers to be exactly where you want them to be when you pour them. Mine where off by about 1/2" each.

Additionally, I also had to make sure that the runners were level. When I put in the forms for the concrete I tried to ensure that they were level, I was off a little bit on some of them though.


For ones that were too low (2-3) I used composite shims from Home Depot to raise them up a bit. There was one pier that was too high. I used an angle grinder to carefully lower it by a quarter inch. I had to be careful not to hit the bolt in the middle as I did this.

Once the runners were placed into the post bases I secured them using the 4 screw holes on each side of the post base.



Step 2 - Framing the Subfloor

Subfloor model

The videos I linked above provide a good overview of how to do this part. Since the runners are already secured it is fairly easy to line up all the boards and start screwing them together. I started by building a box and using this method to make sure it was square. Essentially, you just make sure that the distance from one diagonal of the square equals the other. Then you know that the box is perfectly square. Then in order to line it up on the runners, I screwed two boards on temporarily so that I could move it back and forth to get the box lined up while still being square.

Lining up

Once the box was complete, it was easy to add in the rest of the boards. I got them into place roughly on both sides and then went down each side screwing them into their exact positions. This was pretty easy to do and fun.

Starting to place floor joists

I also screwed the joists down to the runners in a few places for added stability. I used some 90 degree brackets to connect the subfloor joists directly to the runners.

Joists to runners

Step 3 - Plywood

Next, I placed the 3/4 inch plywood on the subfloor framing and screwed it down every 6 inches or so. One thing I forgot to do that I regret is not adding liquidnails between the framing and the plywood. The floor has a slight creak to it which would not be the case if I had remembered to but liquid nails along the floor joists before adding the plywood on top. Also, note in the image how the plywood is staggered so that none of the joints line up. This means that I cut one of the 4x8 sheets in half for the middle section.



Of all the steps involved in building the shed, I think this was the easiest. It ended up being quite a bit easier than I thought.