How to Build a Subfloor for a Shed

Now that you have decided which type of foundation to build for your shed, you are ready for the next step which is building a subfloor. You might think that a floor for a shed is not that important, in some respects you would be right. However you have to think about the longevity of the shed and what you will be using it for. Some people don't put anything on the floor of a shed while others might put a lawn tractor, trailer, snowblower or some other type of heavy equipment. If you have chosen a concrete slab for the foundation you may want to just go right to building the walls unless you want a more finished look for the floor. You at least want your shed floor to be sturdy enough to hold the weight of you while you are inside it. A sagging shed floor is not a good floor and will fail completely before too long.

First you need to frame the perimeter of the floor by cutting 2x6 with a circular saw to make the header and end joists. Assemble the frame by driving two 10d (3 inch) nails into each corner. You want your header joists to come to the end of the frame so remember to cut the end joist 3 inches short to fit between the two header joists. Set the frame in place on the foundation and check for square by measuring across opposite corners. Adjust the frame as needed until the two diagonal distances are exactly the same. Once you are sure the frame is square and level you can move on to the next step.

Nail a corner bracket at each corner of the frame to reinforce the joint. Secure the frame to the skids with hurricane ties. Hurricane ties are basically joist hangers in different forms and can be found at any hardware store. After applying the ties check the corner for square, you can never check for square too much, it is too important to overlook. Next, mark the joist positions every 16 inches on the opposing header joists. Extend the lines down the inside face of the header joists with a combination square. You want to bring the lines down so that you can be accurate where you place your joists. This step is really overkill but I think it makes it easier to see the line. Center a joist hanger at each mark and drive your nails through the flange on one side of the hanger. You want to do this so the joist can be inserted without a struggle.

Now you are ready to make and insert the joists. First cut 2x6 joists to length and sit them in the hangers. Once the joist is in position, press the hanger closed and nail the other flange to the header joist and then to the sides of the joist itself. Continue this process until all the joists are laid out and installed. Now you are ready for the subfloor material. Lay 3/4 inch exterior grade plywood on the joists and trim the panels so that joints are staggered and they fall at the center of a joist. You don't want an edge of the plywood to be hanging out over nothing, this will create a squishy floor, always place the edges over joists. You also want to keep in mind that the plywood will shrink and swell in the changing climates, so you want to leave a gap of approximately 1/8 inch between panels. Finally fasten the panels to the joists with 8d (2-1/2 inch) nails or 2-1/2 inch deck screws. I personally like to use screws for this application because they tend to hold just a little bit better. Space your fasteners about every 6 inches along the edges of the panels and 12 inches everywhere else.

You know have you floor built for your shed. The process of building a foundation and subfloor is really the hardest part of building a shed. Now you can move on to building that walls and you can start to see your shed take shape. The foundation and floor are really the most important part and the base of the shed, make sure you do these jobs right and take your time. If you have a solid foundation and floor, the rest of the shed will be solid as well. Good luck.