Building a Shed on Skids
This shed is about as simple to buid as a free-standing roofed structure can be. It is completely enclosed to keep things dry inside. Building on skids saves you the work of installing a foundation. The weight of the shed keeps it stable. You’ll need to know the size of the rough openings so you’ll be able to purchase your window and prehung door before you build. A suggested size for the shed is 8 feet by 12 feet.
Tools: Circular saw, handsaw, drill, shovel, level, T-bevel.
View the project. The structure rests on massive skids made of triple 2x8s. The floor framing is made of 2x8 joists, 16 inches on center. The shed uses standard stud construction, with 2x4 studs 16 inches on center. The roof is supported by 2x6 rafters, 24 inches on center, that meet on a 1x6 ridge board at the peak. Collar ties on every other rafter ensure that the walls will not bow outward.
1. Provide a foundation. The skids must be level with each other. Dig parallel trenches, 3 feet longer than the shed’s length, and fill the trenches with 4 inches of well-tamped gravel. Check that the tamped gravel is level.
2. Build and set the skids. Make the skids out of three pressure-treated 2x8s; be sure they have a CCA retention level of at least .40 or have a label that says ground contact. Cut the first piece 32 inches longer than the length of the shed, giving it a decorative cut like the one shown. Use it as a template for the other five pieces. Laminate the pieces together by driving 3-inch deck screws in an alternating pattern every 6 inches. Set the skids on the gravel. Run a string line that touches both ends, and use the 3-4-5 method to check for square. Make sure the skids are level, and level with each other.
Other Foundation Possibilities - This shed will float in areas subject to hard frosts—it will rise up a bit in the winter and settle back down when the ground thaws. Many garages also float, so this is not a problem unless your local building department demands footings that extend below the frostline. Because the skids distribute the weight of the shed over a large area, the foundations under them do not have to be very deep. A standard concrete patio slab, in good condition, will be strong enough. If you live in a dry area with soil that never stays wet for long, you may be able to simply tamp the ground firm and set the skids on top of it.
3. Frame and sheath the floor. Use pressure-treated 2x8s and plywood. Cut two 2x8s to the length of your shed, set them next to each other, and mark for joists that are 16 inches on center. (This means that you must subtract 3/4 inch from each multiple of 16 before making your line. Cut joists to the width of the shed, minus 3 inches, and assemble the framing box with 3-inch deck screws. Use the plywood to make sure the frame is square. Attach plywood to the joists with 1 5/8-inch deck screws.
4. Cut and lay out wall plates. For each wall, begin by cutting the bottom and top plates. Set them next to each other, and lay them out as you did the floor joists.
5. Frame the walls. Have your prehung door and your window on hand, so you know the rough openings for each. Buy pre-cut studs, or cut them to the height of the wall, minus 4 1/2 inches. Note that on either side of the window and the door, cripple studs are used. Assemble the walls on the shed floor or another flat surface. Position the studs on the layout lines, and drive two 3-inch deck screws or 16d nails for each joint. With two or more helpers, raise each wall into position and temporarily brace it so it is plumb in both directions. Fasten the walls together and add the top plate.
Figuring Roof Pitch - The horizontal distance traveled by a rafter is called the roof’s run. The vertical distance, from the top of the wall to the top of the roof, is the rise. The slope of a roof is inches of rise per inches of run. A 6-12 pitch, for instance, means that the roof rises 6 inches for every 12 inches of run. Your building department will probably have pitch requirements, so check with the folks there before building. You may want to duplicate the pitch of your house roof on your shed’s roof. To figure the pitch of an existing roof, use two levels, one held plumb and the other held level, and measure the rise and run.
6. Temporarily prop the ridge. Determine how high your ridge board should be. At each end, firmly anchor a notched piece of 2x8 to the inside of the wall framing. Use a level to make sure the board is plumb. Cut a 1x6 ridge board to the length of the shed and set it in place.
7. Mark for the rafters. Have two helpers hold a 2x6 in place against the ridge board and the top plate while you mark with a pencil. Mark the top cut at the ridge and the birds-mouth cut where the rafter will sit on the top wall plate. You may have to experiment before getting it right.
8. Build the roof. This will be the most time-consuming part of the job. Cut two rafters and test them by holding them in place; joints at the ridge and at the top plate should be tight. Use the first rafter as a template for making the others. Cut 2x6 blocking to 22 1/2 inches so that you will end up with rafters spaced 24 inches on center. Work with at least two helpers, because your structure will be very wobbly at first. Mark layout lines on the top plates and both sides of the ridge. Have the helpers hold the rafters in place as you attach. Drive nails through the ridge and into the rafters, and toenail at the birds-mouth cut. Install the blocking as you go. Every other rafter, install a collar tie linking rafters from one sidewall to the other. Cut and notch 2x4 gable studs to fit. Attach the plywood sheathing with 8d nails. Let it overhang the gable ends by 1 1/2 inches. Immediately cover the sheathing with roofing material.
9. Install window and siding - Attach the window to the framing; check for plumb and square before driving screws. Attach 5/8 inch T-111 siding directly to the studs with 8d siding nails, 6 inches apart on the edges, and 12 inches apart elsewhere. Leave a 1/8-inch gap between the siding and the window frame, and caulk it. Trim the corners with 1x3 and 1x4.
10. Install a prehung door. Buy a solid-core, exterior door with a lockset that will withstand weather. Attach the hinge side of the jamb first, checking for plumb and driving 8d casing nails. Make the front edge of the jamb flush with the siding. Shim and attach the other side of the jamb so the door closes easily. Add Z flashing above the door and attach brick molding over the jamb and siding.
11. Add a landing. Start with a ledger board attached to the shed, and support the front of the 2x4 frame with posts sunk in concrete or tamped soil. To keep rain and snow out of the shed, make sure that the top of the finished landing will be an inch or so below the interior floor.