How To Construct Foundations For Your Shed

Whatever shed you choose to buy, it's important to make sure there's a strong base and here's our guide on how to construct timber and concrete foundations.

Created by Nathan James Dodd on Friday, 22nd of August, 2014.
Updated on Thursday, 20th of November, 2014.

Before you begin, look through any instructions and familiarise yourself with the shed's overall dimensions and assembly procedure. As you will be excavating earth, it's also wise to check for any underground cables or drains to avoid damaging them.

Try to choose a site where the land slopes away for better drainage and don't forget in addition to everyday tools such as spade, mallet and tape measure, you'll need some durable plastic sheeting to provide a moisture barrier and wooden stakes.

How To Construct Concrete Foundations

The base needs to be slightly larger than the shed, so add 2ins – 3ins to the dimensions and drive a stake into the ground at each corner. The area within the stakes now needs to be excavated to a depth of least 6 inches.

Checking that the stakes are correctly positioned including the extra few inches, now drive them into the ground so that they are just above the top of the excavation.

Nail plywood strips flush with the top of the stakes along the edge of the excavation, this forms what is called 'shuttering', a sort of mould for the concrete. There should also be extra stakes at a distance of 8 – 10 inches to keep the plywood in place when the shuttering is filled with gravel and concrete..

Fill the frame with crushed gravel to about half its depth and then lay plastic over the top to act as a damp course. For heavy structures you may also need wire mesh above the plastic, but ensure it doesn't pierce the plastic. Now fill the remaining depth with concrete, levelling it off with a board and dispersing air pockets.

Allow about a week for the concrete to cure before assembling the shed.

Constructing Timber Foundations

Assemble a level wooden foundation to the shed dimensions on a flat surface such as a drive or garage floor.

Mark out the site where the shed is going to be located with stakes, extending the width and depth by about 10 inches. Excavate the area to a depth of about 4 - 6 inches. Line the bottom with plastic sheeting and fill in with crushed gravel, making sure it is spread evenly.

Anchor the wooden foundation you made earlier in the centre of the gravel and then assemble the shed.

The Importance Of A Damp Proof Membrane

Metal or single walled vinyl clad sheds will suffer from condensation if any dampness is present and that's why plastic sheeting is so important. If you don't have any damp proofing, any moisture in the foundations, will enter the shed and react with the warmer air to cause condensation.

The condensation cycle is difficult to stop. Therefore, it is vital to prevent it as far as possible in the first place. For further information on condensation prevention, see our blog.

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