Experts in Garden Building and concrete preparation

How to Convert an Old Concrete Patio into a Shed Base

If you’ve got an unused concrete patio and need extra outdoor storage, repurposing it as a shed base can be a smart and cost-effective solution. But not all patios are ready for the load of a garden building without proper checks and prep.

In this guide, we cover everything you need to know about turning an existing patio into a strong, level, and weatherproof base for a garden shed, the right way for UK homes.

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Is Your Patio Suitable as a Shed Base?

Not every patio is ready to become a shed base as-is. Here’s what to check before starting the conversion.

Level and Flat Surface

A shed needs a flat, even surface to sit on. Check for slope, dips, or raised slabs across the area. Minor differences can be corrected with levelling compound, but major unevenness may require grinding or partial slab removal. Use a long spirit level to check the full length and width of your patio.

Structural Condition of the Slabs

The concrete needs to be free from major cracks, crumbling edges, or movement. A cracked or broken patio won’t provide stable support for a heavy shed and may worsen over time. Walk the area and listen for hollow or rocking slabs, which may need replacing or relaying.

Drainage and Moisture Flow

Water should not pool or run toward the planned shed location. Poor drainage under a shed leads to moisture build-up, rot, and damp. Check if your patio has a slight fall to allow water to drain away and consider installing a damp-proof membrane or raising the shed slightly off the surface using bearers or spacers.

Size and Layout Compatibility

Make sure the patio area is large enough to accommodate your shed with room around the sides for airflow and maintenance access. Most UK sheds need at least a 150mm gap from fences or walls, so factor that into your planning. Measure twice, shed bases can’t be easily adjusted once built.

Planning Permission Considerations

For most garden sheds on a ground-level patio, planning permission isn’t needed. However, if you live in a conservation area or plan to install a larger or taller shed, it’s worth checking with your local council. Also, confirm your patio is outside any damp-proof course line of your property.

Steps to Convert Your Patio into a Shed Base

1. Clear and Clean the Area

Remove furniture, debris, and anything stored on the patio.
Pressure wash the surface to remove algae, moss, or grease so you can assess the condition accurately.

2. Level the Surface if Needed

Use a self-levelling concrete compound to fill shallow dips or high spots.
If there are serious slopes, you may need to grind or rebuild part of the patio for proper shed alignment.

3. Lay a Damp-Proof Membrane (Optional)

Roll out a plastic DPM to act as a moisture barrier between the shed and concrete.
Secure with adhesive or timber batten frame, especially useful if the shed has a timber floor or base frame.

4. Install Shed Base Bearers or Frame

Timber bearers or metal frames create airflow beneath the shed and protect against rising damp.
Use spirit level to ensure everything is flat before building your shed on top.

5. Anchor the Shed to the Base

Use expansion bolts or heavy-duty anchors to fix your shed to the patio if needed, especially in exposed gardens or for large buildings.
Follow the shed manufacturer’s guide for recommended fixings and supports.

6. Seal Edges and Apply Finishing Touches

Fill any exposed gaps between the shed base and patio with silicone or weatherproof sealant.
You can also paint or seal the surrounding patio to improve appearance and extend its lifespan.

Frequently Asked Questions

Only if it’s level, structurally sound, and well-drained. A damaged or sloped patio may not be suitable without repair or levelling. Always inspect the condition before building on top.

It’s highly recommended, especially in windy areas. Anchoring prevents movement and improves stability. Some sheds come with pre-drilled base rails for this purpose.

Minor dips can be corrected using levelling compound or timber shims under shed bearers. For anything beyond 10–15mm slope, consider grinding or laying a new base frame.

Only if water is allowed to pool underneath or around the shed. Use bearers or membranes to raise the shed slightly and ensure the patio drains water away properly.

Yes, plastic sheds work well on concrete, provided the base is flat and dry. Many come with bolt-down options or floor panels that rest directly on the slab.