A garden shed with a slope to the floor and roof may look unattractive and detract from the look of the backyard. The original construction may have been faulty, or the ground may have settled under one of the shed's foundation beams. The process of levelling the shed varies depending on the foundation construction methods. This method is not applicable for a shed attached to a concrete slab floor but can be used to level sheds with wood floors resting on wood beam or concrete supports.
Check the level of the shed floor with a 4-foot carpenter's level. Determine the low end spot in the shed and estimate the amount of deflection. Raise the low end of the level until the bubble is in the centre of the lines. Note the distance the end of the level is off the floor. This is the amount the shed floor drops in 4 feet. From this you can estimate the amount the low side or corner of the shed should be raised by multiplying the number of length of the shed, in feet, divided by 4.
Place jacks under the low spot on the shed. This may require multiple jacks if an entire side or end of the shed is low. Car jacks will work for most small sheds, although hydraulic jacks available from a rental store may be necessary for heavier sheds.
Raise the jacks until the shed is level. Use the 4-foot carpenter's level to check the level of the shed.
Add gravel under the support beams of the shed until the beam is in firm contact with the bottom of the shed. Optionally, add shims to the top of the beam or concrete blocks to increase the height of the support. Use treated 1-inch or 2-inch thick boards for larger spaces. Single or multiple layers of asphalt shingles work as shims in smaller gaps. Fill the gap between the shed and the beam or concrete supports.
Lower the jacks and check the level of the shed. Use the jacks to raise the shed again and adjust if necessary.
Adding shims on top of the beam or concrete supports leaves those support members undisturbed. If the support members have settled, they may be in a firmer position than if they are raised and gravel is added under them.
Keep hands and fingers out of the gap between the shed and the support member. If a jack should slip of fail, the shed will fall on the support. Sheds falling an inch or two won't be damaged. Fingers in that gap won't fare so well.