Concrete guidance on floor systems for sheds

December 14, 2012

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, N.C.

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.

The floor of the shed is very important. You want one that can handle water. You might bring in a garden tractor or tools dripping with water. I used to pull my garden tractor into my shed with snow caked on the machine and the plow. When the temperature rose, the snow melt made big puddles of water in my shed.

Your wife will probably want a sink in her shed that is fed by a garden hose, and that means water is going to be on the floor of that shed.

I don’t know how big your sheds will be, but if they’re 10 feet by 12 feet in size or smaller, you can pour a concrete slab with ease under the following conditions:

First, 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 will need just one unskilled laborer to help you place the concrete, a job that should take less than an hour. Once the concrete has been poured, screeded and bull floated, one man can easily finish a 10-by-12-foot slab.

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 it doesn’t crack and break apart.

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 sheds with treated wood floors, and both have stood the test of time.

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 six 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.

I prefer to install closed-cell foam insulation in between the floor joists 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. Without a barrier, water vapor can enter the shed through the floor, which can rust the tools stored there.

Many people don’t realize you can buy treated plywood. You rarely find this at home centers, but traditional lumberyards usually stock this fantastic product. You’ll need an extra sheet or two to make a low-slope ramp to get you in and out of the shed.

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.

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site at www.askthebuilder.com.

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