Q&A / 

Shed Floor Material

Shed Floor Material

This large storage shed under construction has a treated wood floor system. It's just one possible option. ©2017 Tim Carter

Shed Floor Material TIPS

DEAR TIM: I'm going to build a storage shed. Actually I'm building two sheds, as my wife wants her own cute garden shed.

I'm not able to get much help for these projects and am wondering what to do about the floor of each shed. I want them to be waterproof, but I can't even imagine pouring a concrete slab myself.

What are my options when it comes to building a shed with a waterproof floor that will stand the test of time? Al H., Asheville, NC

DEAR AL: I commend you on thinking ahead about the durability and longevity of your shed. All too often people just throw something together and fail to realize what things could look like 30 or 50 years down the road.

Wood & Water Bad Juju

The floor of the shed is absolutely important. You bet you want a floor that can handle water. You might bring in a dripping wet garden tractor covered with water. I used to pull my garden tractor into my shed caked with snow on the machine and the plow. When the temperature rose, puddles of water would be in my shed.

CLICK HERE to get FREE & FAST BIDS from local shed builders.

Your wife will probably want a sink in her shed that's fed by a garden hose. You know that water on the floor of that shed is going to happen like the sun is going to rise tomorrow.

Concrete Is Possible

I don't know how big your sheds will be, but if they're 10 x 12 foot in size or smaller, you can pour a concrete slab with ease if the following conditions exist.

If the concrete truck can pull up to the shed location eliminating the need to wheelbarrow the concrete, you'll be in great shape. Second, you have to have just one fairly unskilled laborer who'll help you for less than an hour place the concrete. Once the concrete has been poured, has been screeded and bullfloated, one man can easily finish a 10 x 12-foot slab.

Concrete Floor Video Series

Watch these following videos to see how easy it is to pour a small concrete slab.

Vapor Barrier

If you do decide you can tackle a concrete slab, be sure to put a high-quality vapor barrier under the concrete. You don't want water vapor from the soil permeating into the shed. Also be sure the slab contains reinforcing steel so the slab doesn't crack and break apart.

The best vapor barriers are cross-laminated virgin vinyl ones. I've had great success with Tru-Tuf. CLICK HERE to ORDER IT.

Treated Plywood

If you can't pour concrete, you can have a waterproof shed floor with little effort. The best part is that you can do this completely by yourself.

You can install a treated wood floor system that will not rot and will give you peace of mind for decades, if not longer. I've built sheds with concrete floors and treated wood floors and both have stood the test of time.

Treated Joists Too

A waterproof wood floor system for a shed starts with a floor framing system just like an outdoor deck. You use treated lumber floor joists that are raised up off the soil. I like to have at least 6 inches of air space between the bottom of the floor joists and the top of the soil.

This space allows foxes and other animals to keep mice away. It also allows you to deal with critters that might want to set up a homestead under the shed.

CLICK HERE to get FREE & FAST BIDS from local shed builders.

Closed Cell Foam

I then prefer to install closed-cell foam insulation in between the floor joists that's located just under the treated plywood that is nailed to the top of the floor joists.

The closed cell foam insulation provides superior energy savings and comfort in case you decide to heat the sheds.

It's also an amazing vapor barrier that stops water vapor from entering the shed through the floor. This water vapor can rust tools that you store in the shed.

Visit Real Lumber Yard

Many people don't realize you can purchase treated plywood. You rarely find this at home centers, but traditional lumber yards almost always stock this fantastic product. You'll need a extra sheet or two to make a low-slope ramp to get you in and out of the shed.

Concrete Piers

The entire floor system can rest on concrete piers that rise up out of the ground. You can also connect the wood floor system to wood posts that rest on concrete piers.

Be sure to use approved hold-down anchors to connect the floor system to the buried concrete footers. You don't want your shed tumbling across your yard in a severe windstorm.

Treated Lumber Bottom Plates

When I frame the walls of my sheds, I always use treated lumber for the bottom plates. This is necessary for concrete, but it's a best practice on a wood-floor system. The reason you want treated lumber for a bottom plate is because no matter what floor you have, it's possible for liquid water to flow across the floor and contact the bottom plate.

You never want the possibility of the bottom plate rotting out. Not only is it hard to replace this critical framing element, it's also very time consuming. The cost to use treated lumber vs. regular lumber is just a few dollars.

Shed Building Videos

You can get access to a series of videos that show you how to build a shed, including a wood floor system. Simply click on this link "shed videos".

I also have a complete set of step-by-step videos for building a shed. I completed the shed this year and videoed each step. The videos are broken down into the various aspects of the shed construction. The complete video series is available for purchase at my AsktheBuilder Store. Just click here for the Shed Building Videos.

CLICK HERE to get FREE & FAST BIDS from local shed builders.

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19 Responses to Shed Floor Material

  1. "I then prefer to install closed-cell foam insulation." It would be helpful to include more information about this product.

  2. Can you please supply a little more information on this paragraph, I am building a shed in north central Florida and want to build the best shed that I can.
    Thank you, Stan.

    Closed Cell Foam
    I then prefer to install closed-cell foam insulation in between the floor joists that's located just under the treated plywood that is nailed to the top of the floor joists. The foam insulation provides superior energy savings and comfort in case you decide to heat the sheds.
    It's also an amazing vapor barrier that stops water vapor from entering the shed through the floor. This water vapor can rust tools that you store in the shed.

    • Hey Stan,

      I'm about a year late to your post, but I'm also in NCFL and prefer to use EPS (floating dock foam). There's always somebody selling it on craig's list for dirt cheap in whatever size you want. Tack a few nails in the sides of the joists at the right depth and just let it hang... if you want to get fancy then spray some great stuff in the cracks. It lasts for several decades under a dock with full water contact, so it's durable enough in my book.

  3. Hello, i am inquiring as to what you would recommend as a floor for a outdoor shed in CT. It is coming pre-built. It has pressure treated floor joists & also a pressure treated plywood floor. This is going to be an entertaining space and i would like to put something over the plywood floor. Any recommendations on what would be the best choice, winters can be cold in CT and summers can be humid. There will be heat in the shed but it won't be on 24/7 in the winter. There will most likely not be AC, just a fan. Thanks much

  4. Hi! I just got a prebuilt 10x10 shed installed which has treated plywood floors. A riding mower, garden tools, and gasoline cans will be stored there. High temperature/humidity will be a year round factor as I am located in South Florida. I was thinking about putting down sheet vinyl to protect the plywood, would this be appropriate? If so, should it be secured with adhesive? If not, what would you recommend? Thanks!

  5. I want to build an 18 - 24 shed for my tractor, snow blower, and smaller outside equipment. However, i will also make half the shed my work area where my workbench, power tools, and tool boxes will be. I am going to place a cement slab down, but should I also build a wood floor for my comfort? Are there other options?

  6. I am building a 14 x 16 shed on a sloped lot with (9) wooden posts buried and supported by concrete. Since the lot is sloped, most (not all) of the joists will have good air circulation. Joists will be in the ground near the higher ground. I would like to use T&G flooring over OSB subfloor, but I am concerned that if the OSB is not treated, it will rot or be attacked by termites. Is treated plywood a better choice for a subfloor and do I need a vapor barrier under that? If I install a vapor barrier and it gets rained on while under construction, won't that trap rain water and cause a problem later?

  7. Tim, first great advice and informational videos. I have an old section of concrete driveway that I would like to build a 10'x12' shed on top of. The slab is about 4" thick and as best as I can tell (metal detector) has wire mesh or rebar reinforcement. Eventually I would like to use this shed as a little work shop so it will be heated.

    Option 1 - Block out a perimeter with cinder blocks and build walls on top of that using the existing driveway as the floor of the shed. I am concerned that far too much moisture will come through the floor. As well this will not be efficient for energy use.

    Option 2 - Build a pressure treated sub frame to sit on top of the concrete and then insulate and build everything up per your article. Should I be concerned having the frame directly on top of the concrete? Is air flow under the shed absolutely recommended? Is it stupid to think I could use a mortar or poly urethane caulk between the frame and concrete to assure any water doesn't run under the shed?

    On a side note I see the Tuff Sheds which have a galvanized metal base frame structure. I think they are made from 14Ga metal framing studs. Any thoughts on doing something like this instead of pressure treated?

  8. Hi Tim, Thank you for your most helpful advice! We were able to check a number of questions off our list from this post. We do have one question for you. We are building our storage barn in northern Michigan and while it will start out being a place for tractor storage, it will end up being used for a few farm animals. As such, we are concerned about the open space under the floor. Is there a process we could use that would still allow air flow, yet keep critters out?

  9. Tim, I am just now finding your site and tutorials after building an alluminum arrow shed with non-treated osb and no sill plate. It's just sitting on the osb floor. Smh. And now water comes in at the edges under the frame 6-8 inches. Anything I can do at this point to stop the water? Is there a heavy caulk I can apply to the inside and outside edge of the frame? Thanks for your service.

    • I'd have to see a photo to give you a great answer. I need to really see what's going on.

      My guess is you're doomed. What a damn shame you didn't look all this up before you started. Send me a photo via my Ask Tim page.

  10. Hi Tim. Great videos. I can't wait to get started! One little domestic debate on this ... air flow under the shed. One of us really wants to conceal the concrete deck blocks with some sort of a brick "skirt" (to prevent any sort of critter from making a home under the shed). And one of us wants to leave it wide open for air circulation. Is there any middle ground (hide the blocks AND get air circulation ... crawl space vents maybe)? Thanks!

  11. Our shed supplier uses PT lumber for the frame and normal plywood flooring over it. Either Prostruct or PT plywood are available as options for the same upcharge. My shed use will be storage - snowblower, mower, yard stuff, etc.
    Do you have a preference for Prostruct or PT plywood in this use?

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