How to Make a 12 by 15 Foot Shed

You can make a lawn or garden shed any size you want, depending mainly on how you will use it and what you will store in it. The basic construction is the same, whether it's a 6-foot-square potting shed or a 12-foot-by-15-foot shed that can store lawn tractors, supplies and other large objects and materials. Start by checking local regulations; most communities require a building permit for a shed larger than 100 square feet. Also check for any underground utilities, overhead power or communications lines that might be in the way.

Things You'll Need

• Rake
• 2-by-4-inch framing lumber
• Circular saw
• Hammer
• Framing nails
• Framing square
• Tape measure
• 4-foot level
• 4-inch-thick solid concrete blocks
• 4-by-4-inch pressure-treated beams
• Metal joist hangers
• 3/4-inch plywood
• 1 1/2-inch galvanized nails
• 2-by-6-inch door header
• Reciprocal saw
• Truss gussets, wood or metal
• Hurricane clips
• 1/2-inch oriented strand board (OSB)
• Roofing paper
• Construction stapler
• Shingles, with peak caps
• Utility knife or big shears
• Wood siding, clapboard planks or tongue-and-groove
• 1-by-4-inch trim boards
• Pre-hung door
• Long screws
• Screw gun

Instructions

1. Rake the shed area clear of any leaves or other debris and smooth and level it as much as possible. Check drainage; avoid any locations where water flows during a rain and be certain the ground slopes away from the shed in all directions. Test the soil; avoid any that has fill material, is mushy or very sandy and unstable.

2. Build a 12-foot by 15-foot outline of 2-by-4-inch framing lumber to serve as a guide for concrete block piers. Make the ends 12 feet wide; cut boards with a circular saw to 14 feet 9 inches for the sides. Nail those into a rectangle with a hammer and framing nails. Use a framer's square to square the corners, then check by measuring with a tape measure from corner to corner and adjusting the frame until those diagonals are equal.

3. Lay the form in the shed location in the desired position. Lay a long board with a 4-foot level on it across the form and adjust the soil until it is level in all directions. Lay three rows of 4-inch thick solid concrete blocks inside the form, one block at each corner, one in the center of each wall and two more inside each row, with centers 24 inches in from the end of the form. Place the blocks lengthwise aligned with the long side of the form.

4. Level the blocks with the long board and level; adjust the soil under them until they are level in all directions. Cut 16-foot 4-by-4-inch beams with a circular saw to 15 feet long and lay them on top of the blocks. Put the beams in the center of the blocks. Check each beam for level, both lengthwise and across the shed.

5. Remove the frame and install 2-by-4-inch joists inside the length of the frame. Cut 2-by-4s to 11 feet 9 inches to fit inside the side bands. Use joist hangers, metal brackets fastened to the side bands, to hold the joists. Space joists 24 inches apart from the front of the shed; the last joist space will be less than 24 inches to the end band.

6. Set the frame on the blocks and toenail the joists to the beams with framing nails driven diagonally with a hammer. Cover the frame with 3/4-inch plywood for a floor, with the top grain going across the joists. Use three 4-by-8-foot panels, alternating seams -- two panels flush with the front wall, the third flush with the back wall -- and cut other panels to fill the gaps on the ends. Secure the flooring with 1 1/2-inch nails to the rafters.

7. Build end walls with 12-foot 2-by-4s for top and bottom plates and side walls with top and bottom plates cut to 14 feet 5 inches (to allow for the end walls). Make rectangular wall frames first with top and bottom plates and end studs, square those corners, then add interior studs spaced on center 16 inches apart. The last side studs will be less than 16-inch spaces.

8. Frame a door in one end wall. Nail a 2-by-6-inch header board between two studs at the height for a pre-hung door. Level that header and fasten it with nails through the studs. Cut two studs to fit between the bottom of the header and the bottom plate and nail those to the header and the outside studs. Install short studs 16 inches apart between the top of the header and the top wall plate. Use a reciprocal saw to cut out the bottom plate inside the door opening.

9. Erect the walls one at a time. Set each wall plumb, with a level, and brace it with 2-by-4s nailed to studs and to stakes in the ground. Secure walls once plumb with framing nails through the bottom plates into the floor joists and bands and nail corner studs together. Tie the walls together with cap boards on top of the wall plates. Use 16-foot boards on the side walls, to overlap the end walls, and boards cut to 11 feet 5 inches on the end walls.

10. Make roof trusses by cutting rafters, securing the peaks with gussets, wood or metal plates that overlap the joints, and cross ties, horizontal braces between the rafters below the peak. Cut rafters to a 4/12 pitch, a roof that rises 4 inches per foot, using a framing square. Put the point of the square at the bottom of a 2-by-4 with the 4-inch mark on the thin tongue and the 12-inch mark on the wide blade at the top of the board. Mark the angle at the end for a top or plumb cut.

11. Measure 75 3/4 inches down the rafter from the plumb cut. Use the square to draw a line 1 inch up into the rafter at that point, then measure 3 1/2 inches back up from the bottom of that line and draw a triangle connecting that point with the top of the line. Add a foot for an overhang and mark an angle reverse of the plumb cut by setting the point of the square at the top of the board. Cut all those angles with a circular saw, then use that as a pattern to cut 16 rafters to make eight trusses.

12. Lay rafters on a driveway or other flat surface, one pair at a time. Put the plumb cuts flush together so they form a proper angle to the side walls; measure between the triangle notches to test this. Fasten the peak with a wood or metal gusset (a triangular piece) overlapping the peak. Cut a 2-by-4 with angled ends to fit between the rafters and secure that to each rafter with gussets. Turn the truss over and add gussets on all joints on the other side. Make eight trusses.

13. Lift trusses to the roof, one at a time, starting at the back. Set the truss plumb with a level, and nail it to the wall on each side through the triangle bearing point. Put a second truss at the other end of the roof, then add trusses in between, spaced 24 inches apart; the last truss will be less than 24 inches to the end. Secure trusses to walls with hurricane clips, metal brackets that overlap truss rafters and wall caps, and are nailed to both boards.

14. Put 1/2-inch oriented strand board decking on the trusses, working from the bottom of each side to the peak. Cut the OSB at the peak with a circular saw; cut one panel first and let the second top panel overlap the other board. Nail OSB to trusses with a 1 1/2 -inch galvanized nails.

15. Spread roofing paper over the OSB and staple it in place with a construction stapler. Spread one sheet to overlap the roof peak, fastened on each side. Shingle the roof with three-tab composition shingles. Cut the tabs off one set of shingles with a utility knife or big shears and nail those on the bottom of each side of the roof with the cut end up and the finished end slightly over the side of the OSB. Overlap shingles according to manufacturer's directions to the peak and install cap shingles at the peak, overlapping the roof joint to seal it.

16. Sheath the four walls with wood planking, overlapping clapboard or tongue-and-groove siding. Most planking comes in 16-foot lengths. Cut boards to cover the 15-foot side walls with solid planks. Cut planks as needed to fit the end walls and around the doorframe. Make diagonal cuts to sheath the gable ends on each side; measure these planks individually to ensure angles are correct.

17. Trim wall corners and the side and gable angle roof joints with1-by-4-inch wood trim; overlap the corner boards at the edges to make a tight corner. Install a pre-hung door in the rough frame. Set the door in place, square and level it using tapered wood shims and secure the doorframe to the rough frame with long screws driven with a screw gun through the sides and top. Trim the door with 1-by-4s, either mitered at the top or with side trims cut square with a top board across them.

References

• "Fine Homebuilding"; Firm Foundation for a Backyard Shed; Joseph Truini; April 2003
• Secrets of Shed Building: Building a Shed
• "Popular Mechanics"; 5 Secrets to Building a Better Shed; Joseph Truini; July 2008
• Shed King: How to Build a Shed Roof
• DIY HQ; How to Build a Roof Truss; Tom T.