UK DIY Guide • Paving Slab Base

How to Build a Shed Base With Paving Slabs (UK Guide)

Q: How deep should I dig for a slab shed base?

Dig deep enough for sub-base + bedding + slab thickness. In many UK gardens this is around 150–200mm total, depending on slab thickness and ground conditions.

Q: Is a slab base good for larger sheds?

Yes, if the sub-base is thick enough and properly compacted. For larger sheds, take extra care levelling and consider a heavier-duty sub-base build-up.

Q: Do I need planning permission for a shed?

Often no, but it depends on shed size, height, and location. Check Planning Portal and GOV.UK permitted development technical guidance.

A paving slab shed base is a popular UK option because it’s neat, durable, and doesn’t require pouring a full concrete slab. The secret is simple: great ground prep + perfect levelling. This guide shows you the most reliable method used for garden sheds across the UK.

Design Your Shed Delivery & Installation

Pro tip: The base should be the shed footprint + 50–75mm extra all around. That overhang helps keep rain splash and mud away from the shed walls.

10x8 pent shed with door and two windows in a garden - stable shed starts with a level slab base — A level slab base prevents sticking doors, twisted frames, and pooling water under the shed.

Why choose paving slabs for a shed base?

Paving slabs are ideal if you want a clean finish and a firm, long-lasting platform without the cost and mess of a full concrete pour. A well-built slab base:

Creates a flat, stable surface for your shed floor and bearers
Can be built in stages (weekend-friendly)
Looks tidy and makes it easier to keep the shed perimeter clear

If you’re ever unsure about whether your shed/outbuilding needs permission, start with official guidance: Planning Portal – Outbuildings and GOV.UK – Permitted development technical guidance.

7x6 timber pent shed side angle with secure hinges - airflow under shed base reduces damp — Even on slabs, using bearers helps airflow and reduces damp risk under the floor.

UK slab base specs (depths, layers & sizes)

These specs suit most UK gardens and typical timber sheds. Soft ground, slopes, or heavier buildings may need extra depth and reinforcement.

Layer	What to use	Typical thickness
Excavation	Remove turf/topsoil to firm ground	Usually 150–200mm total depth (depending on slab thickness)
Sub-base	MOT Type 1 (well compacted)	~100mm (more on softer ground)
Bedding layer	Mortar bed or sharp sand/grit bedding*	25–40mm
Paving slabs	Concrete paving flags	Varies (often 35–50mm)

Bedding choice: Many UK installers prefer a full mortar bed for best support and fewer rocking slabs. For manufacturer installation principles (excavation, sub-base, bedding, levels), see: Marshalls – Concrete paving installation guidelines (PDF) .

For extra reading on practical slab laying techniques (sub-base, bedding, levelling), this is a widely used reference: Pavingexpert – How to lay flags and slabs.

Tools & materials checklist

Materials

Geotextile membrane (weed control + separation)
MOT Type 1 sub-base
Sharp sand / grit sand and cement (if using mortar)
Paving slabs (choose a size that fits your shed footprint neatly)
Timber boards for edging (optional but helpful for clean lines)

Tools

Spade, rake, wheelbarrow
Compactor plate (best) or hand tamper
Spirit level (long), straight edge, string line
Rubber mallet

Ordering a new shed soon? Start here: Shop All Sheds Pent Sheds Apex Sheds

15x8 pent shed with extension and multiple windows - larger sheds benefit from careful slab base levelling — Larger sheds highlight small base errors—take your time on compaction and levelling.

Step-by-step: How to build a shed base with paving slabs

1) Mark out the area

Peg out the footprint and add 50–75mm all around. Use string lines and check squareness by measuring diagonals.

2) Excavate to firm ground

Remove turf and soft topsoil. Dig deep enough for: sub-base + bedding + slab thickness. On many UK gardens this is around 150–200mm total.

3) Lay membrane + sub-base

Lay a geotextile membrane, then add MOT Type 1 in layers and compact thoroughly. Poor compaction is the #1 reason slab bases sink or go out of level.

4) Add bedding layer

Add a 25–40mm bedding layer. Many DIYers use sharp sand; many professionals use a full mortar bed for best support. Either way, your goal is a consistent, level bedding plane.

5) Lay slabs and level as you go

Start from one corner, place each slab, and tap into level with a rubber mallet. Keep checking:

Front-to-back level
Side-to-side level
Diagonals (to avoid twist)

6) Final checks + install shed on bearers

Re-check the whole base with a long straight edge. When installing the shed, use treated bearers where possible to reduce moisture transfer and improve airflow.

Quick quality test: Place your straight edge across multiple slabs—if you can see daylight under it, you’ve got low/high spots that can cause the shed floor to rock.

Want an easy, done-for-you option? Book Delivery & Installation

Common mistakes (and how to avoid them)

Mistake	What happens	Fix
Skipping membrane	Sub-base mixes with soil, base settles, weeds push through	Install a proper geotextile layer before Type 1.
Not enough compaction	Slabs rock or sink over time	Compact Type 1 in layers; don’t rush.
Base too small	Mud splash, damp lower cladding, poor drainage	Make the base 50–75mm larger all around.
Base not level	Doors stick, frames twist, felt/cladding strains	Level the base (not the shed). Check diagonals and use a straight edge.

If you’re installing something heavier (workshop, motorbike, or security shed), browse: Workshop Sheds Motorbike Sheds Security Sheds

FAQ: Paving slab shed bases

Do paving slabs need mortar for a shed base?

A full mortar bed usually gives the best support and reduces rocking slabs. Sharp sand can work for lighter sheds, but prep and compaction matter more than anything.

How deep should I dig for a slab shed base?

Dig deep enough for sub-base + bedding + slab thickness. For many UK gardens this is around 150–200mm total, depending on your slab thickness and ground conditions.

Is a slab base good for larger sheds?

Yes—if the sub-base is thick enough and properly compacted. For large sheds, take extra care levelling and consider a heavier-duty sub-base build-up.

Do I need planning permission for a shed?

Often no, but it depends on size, height, and location. Check: Planning Portal and GOV.UK technical guidance.