Plywood is probably the most common material used in shed flooring. It’s easy to work with, easy to cut, and doesn’t take half the time to install as plank flooring. While prices have gone up in recent years, it’s still one of the more inexpensive materials you can buy for flooring. If you get the right kind of plywood and take care when installing it, your plywood floor should last as long as the rest of the shed.
Pressure treated plywood is your best option for a long-lasting shed floor, as it is very water resistance and installed correctly will provide a great durable and strong shed floor.
You may think that since your flooring won’t be subjected to the weather, you don’t need to get the pressure treated kind. Your shed floor, however, will be subjected to wet or muddy shoes or boots, the rain blowing in when the door is open, and wet wheels from your lawn tractor or rototiller.
You’re also not likely to get all the snow off your snow blower before you put it away, and water can drip from wet hand tools. Even the wet grass dropping from under your lawn mower can cause problems on untreated plywood. In practice, your shed floor is the part that is likely to get the most abuse while having to hold the most weight. It just makes sense to get the sturdiest flooring you can without blowing up your bank account.
Pros and Cons of Pressure Treated Plywood for a Shed Floor?
Pros: Pressure treated plywood is not entirely waterproof, but it is able to better withstand moisture. This means that the plywood is also resistant to damage or incursion from fungus. In fact, pressure treated wood is treated with chemicals under pressure, one of which is copper based to prevent mold and mildew from taking hold.
Usually, one of the chemicals also is a deterrent to insects, so termites and carpenter ants won’t look at you’re flooring as being tasty.
You can get plywood that is smooth enough on one side so that you can easily sweep up grass clippings and those leaves that blow in. In addition, it makes a good surface to paint if you want to. You can even stain it, as modern pressure treated plywood takes stain better than it did in previous times. Get more information on waterproofing plywood in my article What’s the Best Way to Waterproof Plywood?
Cons: Pressure treated plywood is more expensive than the type that hasn’t been treated, and you will need to get the exterior grade, which will cost a bit more. While pressure treated plywood is moisture resistant, that doesn’t mean that it is moisture-proof. You’ll want to make sure all the edges are treated with wood preservatives, especially any cuts you make.
What is the Best Fastener for Pressure Treated Plywood?
The best fasteners are exterior-grade galvanized screws. This grade of screws ensures that they won’t start to rust in case your shed is humid inside during the summer months. They also won’t react negatively to any of the chemicals used to treat the plywood.
While nails may seem like less work, especially if you use a nail gun, screws do have their advantages. They are less likely to work themselves out of the floor over time as nails sometimes do. Nails that raise their heads a bit tend to allow the flooring to move when stepped on, creating a creaky floor.
In addition, an errant nail head sticking up can catch on something heavy you’re sliding across the floor, catch dirt and debris, and even trip a person under the right circumstances. Check with your supplier as to the right type of screws for your flooring, as certain types are designed just for plywood.
Screws should go about eight inches apart. When putting them along the seams between two sheets, putting them next to each other on both sheets helps prevent their lifting up when weight is put on them. One tip is to lay your floor out completely before fastening. Snap chalk lines on the plywood to tell you where the joists are, and your screw installation will go much more quickly. Check out my article Do I Use Nails or Screws for Attaching Plywood? for more information on plywood fasteners.
Do I Need to Apply Wood Preservative to Cuts Made to Pressure Treated Plywood?
As has been mentioned, even pressure treated plywood is not waterproof. It would be a good idea to plan out any cuts you have to make and cut your pieces first. Then apply a wood preservative to all edges, even the ones made by the factory. Be sure to let it dry and cure thoroughly before installation. That way you can ensure that any moisture getting into the seams won’t affect the plywood.
In fact, after your floor is installed, it wouldn’t be a bad idea to apply a sealant. The problem is that you need to make sure that the plywood is completely dry before application. The chemical treatment leaves a little moisture behind, and this prevents any sealant from working properly.
Since you probably will be installing the flooring before putting up the walls, it would be a good idea to make sure that your plywood is completely dried before working with it so as not to hold up further construction. To test it, pour a little water on a sheet. If it beads up anywhere, that means that there’s still some moisture left, and it needs more drying time.
What Thickness Should Pressure Treated Plywood be For a Floor?
If you plan to have a small shed only used for lightweight items such as handheld garden tools and a bicycle or two, you can get away with ½ inch thick plywood. The best type for a shed floor, however, is 3/4-inch plywood. Remember that your floor will get a lot of abuse, and you’ll end up storing heavy things such as cans of paint, lawn chemicals, bags of fertilizer, and the like. You can get information on how strong 3/4 plywood is in my article How Much Weight Can 3/4 Plywood Hold?
What Grade Should Pressure Treated Plywood be For a Floor?
Construction grade exterior plywood is recommended. Remember that you’ll always be adding to the load of your shed floor over the years as more and more items are stored there, as well as yard machines and perhaps big boy toys such as a snowmobile.
Another way of grading plywood is the finish. Plywood can have two grades per sheet, one for the face veneer, which will be seen, and another grade for the back, which won’t be seen. The grades are as follows:
A-grade – This is the highest quality. This is the kind you may want for the top side of your floor. It’s smooth and easy to paint.
B-grade – This grade is a little less smooth. It may also have minor flaws which will usually be repaired with filler at the factory. There may be cracks that you’ll want to fix with wood filler.
C-grade – This grade has more visible flaws and can contain knots up to 1-1/2 inches in diameter.
D-grade – This is the cheapest finish. It can have large flaws, and the knots can be up to 2-1/2 inches in diameter.
The first letter in a plywood grade denotes the face side, while the second letter grades the back side. You can save money by buying plywood rated as AB or AC.
There is another choice which may be available to you. Plywood also comes in two major types: softwood and hardwood. Hardwood plywood is more durable, but it’s also quite a bit more expensive and may contain some softwood. Construction-grade plywood is made of softwood, but it will do for your shed flooring just fine. Check out my article What’s the Correct Direction for Installing Plywood? to make sure you get the strongest floor as possible.
What Other Options Are There to Pressure Treated Plywood?
Many people use Oriented Strand Board, or OSB, for their shed flooring, mainly because it’s usually cheaper than plywood, but is also a little weaker than plywood of a similar thickness and is more pliable. This means that you’re more likely to have a bouncy floor unless your joists are close together.
Plywood is formed of sheets of wood veneer glued together with each layer having the grain perpendicular to the one above. The pressure treatment comes later, with chemicals being infused under heat and pressure.
OSB is formed from wood strands of various lengths. It makes use of knotty, crooked or deformed trees which aren’t good for lumber. The strands are sorted with the longer ones used for the outer layers. The inner layer is perpendicular to the outer ones. The strands are mixed with resins and wax, then formed into mats which are subjected to pressure and heat.
The problem with OSB comes with moisture. OSB absorbs less moisture than plywood, but it takes longer to dry. Also, when plywood gets damp, the moisture typically spreads out. OSB has a tendency to absorb moisture at the edges and swell. You can buy OSB that is rated as being waterproof, but you’ll still need to treat any cut edges. If it’s not rated as waterproof, it can be coated with sealant. If you considering painting pressure treated wood, check out my article When Can You Paint Pressure Treated Wood?
Choosing your shed flooring is a very important part of building a shed. The floor can get almost as much abuse as your roof and has to last for a long time. You certainly don’t want to have to replace it any time soon, so be sure to get the best kind you can. Pressure treated exterior construction grade plywood is a popular choice. As for the thickness, it’s better to get something thicker rather than thinner. Once you waterproof it and install it, you can forget about it and probably will.