Preparing Your Shed Base

As we noted last time in How to Choose a Garden Shed, all types of sheds will last longer if they’re built properly in the first place.

All sheds are better on a firm base, and this base should be level. Concrete is ideal for long life, slabs are perfectly fine as long as they’re levelled and settled properly, and bricks are also okay if they’re laid down properly.

The shed needs to be fully supported, including the floor, as well as the sides (which may rest on the floor anyway). The joists used in most shed floors are flimsy and not intended to take much unsupported weight, unlike the ones in your house which are probably about eight times as strong. This means they need support with pads at intervals along their length.

Exactly how many 'pads' will be needed will depend on the size of the shed and the sturdiness of its construction. As a rough guide, you'll need pads every two feet for a budget priced shed, while a more substantial one will be okay with pads every three or four feet.

Each pad should be roughly 20 to 30cm (9 to 12 inches) square, in order to spread the load, with a firm base underneath the concrete, stone or bricks. (Note that three bricks on edge are roughly 9 inches square, as is a small paving slab.) If possible, dig down about the same depth as the size of the slab and fill the hole with crushed stone, brick or rubble to give a firm foundation.

Use a spirit level to make sure all the pads are level with each other. A bit of time spent now will repay you many times over in the years to come. Note that concrete needs a few days to harden before you put any real weight on it.

So, first decide what type and size of shed you’re going to have, then get the exact measurements for the base and the distances between the joists so you can position the pads accurately. These dimensions should be in the instructions or specifications, although you'll have a few inches' leeway with the size of your pads.

Do this right to begin with and you'll get many more years of use from your shed.