How to Build a 12X24 Wood Shed

Bob Haring

Building a 12 by 24-foot shed is like building a small house. You must lay a good foundation, build walls, frame windows and doors, make roof rafters or install trusses and finish the outside with siding and roofing. It requires good carpentry skills, as well as tools and help. A big shed is at least a three-person job. It also will take time, probably at least two weeks and a lot of 2-by-4-inch framing lumber plus other material. You can finish the shed with any type of attractive siding and roofing, match the house if you wish.

  1. Pick a location for the shed, preferably fairly flat, with good drainage and easy access from all sides. Mark the perimeter with wood stakes and builder's twine, six inches larger than the shed on all sides. Make sure it is square by measuring corner to corner with a tape measure; if axes are equal, the building is square. Excavate that area with a shovel or mechanical excavator at least eight inches deep and fairly level, with smooth dirt sides. Put in medium gravel, 1/2-3/4 inch, up to ground level, and compact it firmly with a hand or mechanical tamper.

  2. Build a form for a concrete slab foundation to the exact dimensions with 2-by-4s, coated on the inside with mineral oil or similar material to prevent concrete from sticking. Let the long sides of the form overhang, and nail the 12-foot ends inside. Brace the forms with stakes in the ground every two feet. Check with a level to make sure the tops of the forms are level all the way around. Pour concrete to the tops of the form, level it with a long 2-by-4 dragged across the surface and trowel it smooth. Let it cure about one week.

  3. Design walls to include doors, windows and any utilities like electricity. Make walls with a bottom plate of pressure-treated 2-by-4s, a top plate and studs fastened 16 inches apart between the two with a hammer and framing nails. Frame doors and windows with 2-by-6 inch top headers and bracing studs. Build walls on the ground and raise them in place (with lots of help). Brace them plumb with boards nailed to walls and to stakes in the ground. Fasten the bottom plates to the slab with concrete nails, and nail wall corners together. Add wall caps, 2-by-4s nailed over the top plates and overlapping corners to tie the walls together.

  4. Frame a roof with gable rafters, cut using a roofer's square or a rafter table, or with prefabricated trusses. Nail rafters or trusses to wall caps and install a ridge board end-to-end on the rafters or trusses. Add gable stud braces, 2-by-4s nailed between the bottom of the ridge board and the end wall cap. Sheath the sides and roof with oriented strand board (OSB) nailed to studs and rafters. Use a reciprocal saw to cut out door and window openings.

  5. Install doors and windows with metal flashing around the edges to block moisture. Add siding of choice over the OSB; put on a layer of 1-inch foamboard insulation first if the shed needs to be insulated. Use wood planks, plywood panels, vinyl siding or other cladding of your choice. Lay roofing paper on the roof sheathing and nail shingles to the roof, starting at the bottom and working up both sides to the ridge.

  6. Add any trim boards at wall corners, around windows and doors, under the roof eaves. Use 1-by-4 inch boards for trim, overlapping edges at the corners so the long side of the shed will have a 5-inch trim (4-inch board plus 1-inch overlap). Make a ramp if lawn tractors and other big equipment will be stored in the shed. Build interior shelves or cover walls with pegboard to hang tools and other objects.