A shed is only ever as good as the base it sits on. Get the base right and a quality timber building will give you decades of service; get it wrong and you invite damp, rot, sticking doors and a sagging floor. This guide explains how to lay a shed base, compares the two most popular base types, and walks through preparing the ground properly so your shed lasts.
Why the base matters so much
A shed base does three jobs: it keeps the timber floor off wet ground, it spreads the weight evenly so the building stays square, and it provides a flat, level surface so doors and windows open correctly. Skipping or skimping on the base is the single most common reason sheds fail early.
Comparing the two main base types
| Base type | Best for | Pros | Cons |
|---|---|---|---|
| Concrete slab | Large sheds, workshops, heavy use | Permanent, perfectly level, very strong | Costly, hard work, not removable |
| Paving slabs | Small to medium sheds | Firm, level, cheaper than concrete | Needs careful levelling of each slab |
Option 1: Concrete base
A poured concrete slab is the gold standard for larger sheds, workshops and anything heavy. It’s permanent, completely level, and copes with the weight of machinery or a workbench. The downsides are cost, effort, and the fact that it isn’t easily moved or removed. A concrete base should be laid on a compacted hardcore sub-base and allowed to cure fully before the shed goes on.
Option 2: Paving slabs
Paving slabs are a popular middle-ground choice. Laid on a bed of sand or mortar over compacted hardcore, they create a firm, level surface that’s cheaper and less daunting than concrete. They suit small to medium sheds well. The key is getting every slab perfectly level with its neighbours so there are no rocking points.
Why we don’t recommend plastic grid bases
Plastic interlocking grid systems are widely marketed as a quick, easy solution for shed bases, and you’ll find them sold in many DIY stores. We don’t offer them, and we don’t recommend them — here’s why.
The core problem is long-term stability. Plastic grids flex under load, and over time that movement works against the shed frame. Timber buildings need a genuinely rigid, flat platform to stay square; a surface that shifts or gives — even slightly — will cause doors to stick, frames to rack and floors to creak. The more weight you put in the shed, the more pronounced the problem becomes.
There’s also the drainage argument made in their favour: plastic grids are permeable, so water passes through freely. In practice, this matters less than it sounds. A properly prepared hardcore sub-base under concrete or slabs drains well anyway, and the additional few millimetres of permeability that a plastic grid offers rarely makes a meaningful difference to how the shed performs.
Finally, plastic degrades outdoors. UV exposure and ground movement cause joints to become brittle and the grid to sink unevenly over the years — exactly what you don’t want under a building you’ve invested in. We’d rather spend a little more upfront on a concrete slab or paving slabs and know the base will outlast the shed itself.
How to prepare the ground: step by step
Whichever base you choose, the groundwork makes or breaks it. Follow these steps:
- Clear the area — remove all vegetation, turf and topsoil.
- Size it correctly — make the base slightly larger than the shed footprint so rainwater drips clear of the timber.
- Lay a sub-base — compact a hardcore sub-base for stability and drainage.
- Check the level — check for level in both directions, repeatedly. This is the step people rush, and it’s the one that matters most.
- Allow for airflow — make sure air can circulate underneath so the floor can breathe and stay dry.
How to lay a shed base: which option is right for you?
As a rule of thumb: choose concrete for large or heavy buildings and workshops, paving slabs for general-purpose sheds of any size. If in doubt, err towards the more robust option — a stronger base is rarely a wasted investment.
Frequently asked questions
Can I put a shed straight onto grass or soil?
It’s not recommended. Placing a shed directly on grass or soil traps moisture against the timber, leading to rot and an uneven, sinking floor. Always use a proper base.
Does a shed base need to be bigger than the shed?
Yes, slightly. A base a little larger than the footprint lets rainwater drip clear of the walls rather than running back against the timber.
What is the cheapest shed base?
Paving slabs offer a good balance of cost and durability for most sheds. Concrete is the more expensive option but provides the strongest long-term foundation, particularly for larger or heavier buildings.
How long should concrete cure before fitting the shed?
Concrete should be left to cure fully — typically several days — before the building is placed on it, to ensure it reaches proper strength and stays level.
Let us help with installation
Many of our customers prefer us to handle the groundwork and installation as part of their order, so the building arrives, the base is ready, and everything is fitted correctly. Explore our shed range or get in touch to discuss base preparation and installation for your garden.