Footings provide a stable base for a shed. Footings distribute the weight of the shed evenly, prevent it from sinking into the ground and keep it from moving during the seasonal thaw-and-freeze cycles. The required depth of a footing depends on the frost line; frost lines vary from region to region. Verify where your frost line is before creating footings for a shed. Contact a builder in your area to verify the frost line if you are unsure.
Lay out the location for the shed with rope, and then use stakes, a hammer and string to outline the footings for the shed. Footings should be every 10 cm (4 feet) around the base of the shed; the exact number of footings varies depending upon the size of the shed.
Measure to make sure that the staked outlines for the shed footings are square (even) with a level and framing square. Place the level on the straight edges and the framing square on the corners. Adjust as necessary until square.
Remove approximately 15 cm (6 inches) of sod from the area on all sides, and then excavate the trench for each footing approximately 30 cm (12 inches) with a shovel.
Lay a 15 cm (6 inch) layer of compactable gravel subbase into the trench and tamp with a hand tamp. Make sure to tamp the subbase thoroughly.
Place forms on the outline of the footings, aligning the forms with a string. Drive stakes along the outside of the forms to anchor them in position. Adjust the forms until level.
Coat the inside edges of the forms with vegetable oil.
Mix concrete according to the manufacturer's directions. Mix the concrete with a shovel until all air pockets are removed.
Pour the concrete in even loads into the forms. Pour concrete until it reaches the tops of the forms. Do not pour the concrete too close to the edges of the forms.
Screed the concrete in the footings with a 5 by 10 cm (2 by 4 inch) board. Drag the board along the top of the forms. Add concrete to any low areas as you go. Continue until the surface of the concrete is even.
Cover the footings with plastic once the concrete is hard to the touch, and let it cure for two to three days. Remove the forms, and backfill around edges with compactable gravel until the area is level with the surface footings.
Let the footings cure for one week to maximise the strength.