Key Takeaways
- A proper paving slab base prevents your shed from sinking, keeps it level, and extends its lifespan by protecting against moisture damage
- The secret to success is in the preparation – your sub-base matters more than the slabs themselves, and rushing this step will cost you later
- Budget around £50 to £100 for materials for a small to medium shed base (plus your time), making it significantly cheaper than concrete
- Most people underestimate the digging required – expect to remove 15 to 20cm of soil across the entire area, which creates more spoil than you think
- Leave 48 hours for the base to settle before building your shed on top – patience here prevents problems down the line
At a Glance
Best for: Sheds up to 3m x 2.5m, storage buildings, garden offices, workshops
Not ideal for: Very large sheds (over 4m), buildings on slopes without significant levelling, temporary structures
Time needed: Full weekend for first-timers, one long day for experienced DIYers
Cost range: £50 to £100 for small sheds, £150 to £250 for medium-sized bases (materials only)
Difficulty level: Moderate – requires physical effort but straightforward if you follow the steps carefully
What you need: Paving slabs, sharp sand, hardcore or MOT Type 1, basic tools (shovel, spirit level, rubber mallet)
Biggest mistake to avoid: Skimping on the sub-base depth or compaction – this is where most bases fail within the first year
Quick tip: Always add 5 to 10cm extra space around your shed measurements – you will thank yourself later when applying wood treatment
My honest take: This is one of those jobs that looks simple but tests your patience. The digging is harder work than you expect, and getting everything level takes longer than planned. But once it is done, it is done properly.
Planning to put up a shed in your garden? The foundation might not be the exciting bit, but get it wrong and you will be dealing with a wonky shed, rotting timber, and doors that will not close properly within a year or two.
I have built a fair few shed bases over the years (some better than others, if I am being honest), and paving slabs remain my go-to method for most garden buildings. They offer a solid, level surface without the permanence or expense of concrete, and they are genuinely achievable as a DIY project even if you have never laid a slab in your life.
This guide is for anyone who wants to do the job properly without overcomplicating it. If you are after a quick fix or a temporary solution, this probably is not for you. But if you want a base that will still be level in ten years’ time and will not have you cursing your past self every time you open the shed door, then keep reading.
What makes this guide different from the dozens of others you will find online? I am going to tell you about the mistakes I made so you do not repeat them, give you realistic time and cost estimates, and skip the corporate sales pitch. This is the advice I would give a neighbour who asked me how to do it over the garden fence.
Why Use Paving Slabs for a Shed Base?
Before you commit to digging up half your garden, it is worth understanding why paving slabs are such a popular choice for shed bases.
The main advantage is stability without permanence. Unlike a concrete base, you can lift and relay paving slabs if you change your mind about placement or need to access services underneath. They create a solid, level platform that prevents your shed from sinking into the ground, which is exactly what happens when you try to build directly on soil or grass.
Cost is another factor. For a typical 2m by 2m shed base, you are looking at £50 to £100 in materials, compared to £200 or more for a proper concrete base. You are trading money for your own labour, which suits most people.
Paving slabs also drain well if laid correctly. Water runs off between the joints rather than pooling underneath your shed, which keeps the timber dry and prevents rot. This is particularly important in the UK where we get more than our fair share of rain.
The one downside worth mentioning is weight and physical effort. Paving slabs are heavy (a 600mm square concrete slab weighs around 20kg), and you will be moving quite a few of them. This is not a one-person job if you can avoid it.
Choosing the Right Location for Your Shed Base
Get the location right and everything else becomes easier. Choose poorly and you will be fighting drainage issues, tree roots, or access problems for years to come.
Look for ground that is reasonably flat to start with. Yes, you can level a slope, but it means significantly more digging on one side and potentially building up a retaining edge. If your garden has any level areas at all, use one of those.
Stay well clear of trees, particularly large established ones. Tree roots can grow underneath your base and lift the slabs over time. I learned this the hard way with an apple tree that I thought was far enough away. It was not. Allow at least 3 to 4 metres from any sizeable tree.
Think about drainage as well. Do not position your shed in a natural dip where water collects. After heavy rain, watch where the water goes in your garden and avoid those spots. If you have no choice, you will need to consider a French drain or raised base, which adds complexity.
Finally, consider access. You need to be able to walk around your shed to apply wood treatment each year. If you jam it tight against a fence or wall, you are making future maintenance much harder. Leave at least 30cm on all sides if you can.
Tools and Materials You Will Need
Before you start digging, gather everything you need. There is nothing more frustrating than having to stop halfway through because you are missing something essential.
| Item | Purpose | Approximate Cost |
|---|---|---|
| Paving slabs (600mm x 600mm) | Top surface of your base | £3 to £5 each |
| MOT Type 1 or hardcore | Sub-base for stability | £40 to £60 per tonne |
| Sharp sand or building sand | Laying bed for slabs | £3 to £5 per 25kg bag |
| Cement (optional) | Mixed with sand for firmer bed | £5 to £7 per 25kg bag |
| Weed control membrane | Prevents weed growth | £15 to £25 |
| Spirit level (long one if possible) | Checking slabs are level | £10 to £30 |
| Rubber mallet | Tapping slabs into position | £8 to £15 |
| Shovel and rake | Digging and levelling | £20 to £40 for both |
| String line and wooden pegs | Marking out area | £5 to £10 |
| Wheelbarrow | Moving materials | £30 to £60 (or borrow one) |
The table gives you rough costs, but prices vary depending on where you shop. Builder’s merchants often work out cheaper than DIY chains if you are buying in bulk. For a 2m by 2m base, expect to spend somewhere between £80 and £120 all in.
One thing worth investing in is a decent spirit level. A cheap one that is not accurate will make your life miserable. Borrow a long one (at least 1m) from a neighbour if you can – it makes checking across multiple slabs much easier.
Step-by-Step Guide: How to build a shed base with paving slabs
Step 1: Measure and Mark Out Your Area
Measure your shed carefully. Then add 5 to 10cm on each side. This extra space is not optional – you need it for maintenance access and to allow for any slight variations in shed dimensions.
Use wooden pegs at each corner and run string between them to mark your perimeter. The string gives you a visual guide and helps keep your digging straight. Check the area is square by measuring corner to corner diagonally – both measurements should match if you have got a proper rectangle.
This is also your last chance to double-check the location. Stand back and imagine the shed in place. Can you still access the bins? Will it block light to the kitchen window? Is there room to open the shed door fully? Sort out these questions now rather than after you have dug a massive hole.
Step 2: Excavate the Ground
Here is where the reality of the job hits. You need to dig down 15 to 20cm across the entire marked area. For a 2m by 2m base, that is removing roughly 0.6 to 0.8 cubic metres of soil, which is more than you think.
Keep the sides of your excavation as straight as possible – it makes everything else easier. Remove any large stones, roots, or old bits of rubble as you go. Do not just bury them deeper and hope for the best.
The soil you remove creates what is called ‘spoil’, and it bulks up considerably once dug. You will end up with more volume than you started with. Have a plan for this – can it fill a low spot in your garden? Do you need to hire a skip? I once ended up with a massive soil pile that sat there for three months because I had not thought this through.
Step 3: Lay the Weed Membrane
Once you have dug down to depth, lay a weed control membrane across the base of your excavation. This stops weeds pushing up through your hardcore and eventually through the gaps in your slabs.
Is it essential? No. Will you regret not using it when you are pulling out dandelions in two years’ time? Probably. A decent membrane costs £15 to £20 and takes five minutes to lay. Just do it.
Overlap any joints by at least 10cm and bring the membrane up the sides of your excavation slightly. You can trim off any excess once everything is finished.
Step 4: Add and Compact the Sub-Base
This is the most important step, and the one most people rush or skimp on. Your sub-base is what stops your entire base from sinking or shifting over time.
Add roughly 10cm of MOT Type 1 or hardcore. MOT Type 1 is a specific grade of crushed stone that compacts beautifully and is designed for this exact purpose. You can sometimes get away with cheaper hardcore, but MOT Type 1 gives you the best results.
Rake it out as evenly as you can, then compact it thoroughly. If you can hire or borrow a wacker plate, brilliant. If not, use a heavy tamper or even a fence post to bash it down. The aim is to remove all the air pockets and create a solid, stable layer.
Check for level as you go with your spirit level. It does not need to be perfect at this stage, but it should be roughly flat and definitely not sloping in one direction.
Common Mistakes to Avoid When Laying the Sub-Base
- Not compacting enough: If you can still push your thumb into the hardcore easily, it is not compacted enough. Keep going until it feels rock solid.
- Using the wrong material: Gravel or pea shingle will not compact properly. It needs to be angular crushed stone with a mix of sizes.
- Making it too thin: Less than 7 to 8cm of compacted hardcore and you risk the base settling unevenly over time.
- Ignoring drainage: If water pools on your sub-base after rain, you have a problem. The base should be slightly higher than the surrounding ground to encourage water runoff.
Step 5: Add the Sand Laying Bed
On top of your compacted hardcore, add a layer of sharp sand (or a mix of sharp sand and cement if you want a firmer bed). This layer should be about 4 to 5cm deep before you compact it.
The sand mixture I use is 8 parts sharp sand to 1 part cement. Mix it dry – do not add water at this stage. This creates what is called a ‘semi-dry’ bed that firms up gradually once the slabs are in place and moisture gets to it.
Use a rake to spread the sand evenly, then use a straight piece of timber (a long 2×4 works perfectly) to screed it level. Rest the timber on opposite edges of your excavation and drag it across the surface. This gives you a flat, even bed.
Do not walk on the sand bed once it is levelled. Work from the edges and only step on slabs you have already laid.
Step 6: Lay Your First Row of Slabs
Start in one corner and work your way across. Lay your first slab carefully – this one sets the standard for everything else. Use your spirit level to check it is flat in both directions.
Tap it gently into place with your rubber mallet. You want it sitting firmly in the sand bed without rocking, but not buried so deep that it sits lower than it should.
Leave a small gap between slabs – about 3 to 5mm is ideal. You can use pieces of wood or purpose-made spacers to keep the gaps consistent. These gaps allow for slight movement and let water drain away rather than pooling on the surface.
As you add each slab, check it is level both across its own surface and in relation to the slabs you have already laid. Your long spirit level is invaluable here.
Step 7: Continue Laying Slabs Row by Row
Work methodically across your base. After each slab, check the level. If a slab sits too high, lift it off and remove a bit of sand underneath. If it sits too low, add more sand.
This is where patience matters. You might lift and relay the same slab three or four times to get it spot on. That is normal, especially when you are learning. The temptation is to think ‘close enough’ and move on, but those small errors add up. A base that is slightly off level now becomes noticeably wonky once your shed is on top.
Keep your spirit level moving – check forwards and backwards, side to side, and diagonally across multiple slabs. What looks level to your eye often is not once you actually measure it.
Step 8: Fill the Gaps Between Slabs
Once all your slabs are laid and you are happy with the levels, brush kiln-dried sand or dry sharp sand into the gaps between them. This locks everything in place and prevents the slabs from shifting.
Use a soft brush and work the sand into the joints from multiple directions. You want the joints filled right to the top.
Give the whole base a light watering with a garden hose or watering can. This helps the sand settle into any remaining gaps. You might need to add more sand and water again once it has settled fully.
Step 9: Let It Settle
This is the hardest step because it involves doing nothing. Leave your finished base for at least 48 hours before putting your shed on top. Ideally, leave it for a full week if you can.
During this time, avoid walking on it more than necessary. The sand bed needs time to settle and firm up, particularly if you used a sand and cement mix.
If rain is forecast, do not panic. A bit of rain actually helps the base settle and firms up any cement in your sand mix. Heavy rain is less ideal, but modern paving slabs cope fine.
Pro Tips From Experience
- Work in decent weather: Laying slabs in pouring rain is miserable and makes getting the levels right much harder. Wait for a dry spell if you can.
- Get a helper for the heavy slabs: Concrete slabs are surprisingly heavy. Two people make the job twice as fast and much safer.
- Number your slabs before laying: If you need to cut any slabs to fit, number them on the back so you know which goes where. Sounds obvious but easy to forget once you are in the thick of it.
- Use a timber frame if the ground is soft: On very soft or clay-heavy soil, consider adding a timber edging board around your base. This contains the sand and hardcore and stops everything slowly spreading outwards.
- Save some sand and hardcore: Keep a bag of sharp sand and some leftover hardcore. Bases sometimes settle slightly over the first few months, and you might need to lift and re-level the odd slab.
Paving Slabs vs Other Shed Base Options
Paving slabs are not your only option for a shed base. Here is how they stack up against the alternatives.
| Base Type | Cost | Difficulty | Longevity | Best For |
|---|---|---|---|---|
| Paving slabs | Low to moderate | Moderate | 15+ years | Most garden sheds, workshops, offices |
| Concrete | Moderate to high | High | 20+ years | Large sheds, permanent structures |
| Plastic grid base | Moderate | Low | 10+ years | Lighter sheds, quick installations |
| Timber bearers | Low | Low | 5 to 10 years | Temporary sheds, level ground only |
| Directly on grass/soil | None | Very low | 1 to 3 years | Nothing – avoid this |
The table shows that paving slabs hit a sweet spot between cost, difficulty, and longevity. Concrete lasts longer but costs significantly more and requires more skill to get right. Plastic grids are easier but less stable for heavier sheds. Timber bearers work on perfectly level ground but rot over time.
Placing a shed directly on grass or soil might seem like a shortcut, but it really is not worth it. The timber base will rot within a couple of years, doors will start sticking as the shed sinks unevenly, and you will end up rebuilding the whole thing. Do it properly once rather than bodging it twice.
What Can Go Wrong and How to Fix It
Even with careful work, things sometimes do not go to plan. Here are the most common issues and what to do about them.
The Base Ends Up Slightly Unlevel
Small variations (a few millimetres) across a base are not the end of the world. Your shed will still sit fine. Bigger gaps (10mm or more) should be fixed, especially if they create a slope in one direction.
The fix is to lift the affected slabs, adjust the sand underneath, and relay them. Do this before you put the shed up, while it is still easy to access everything.
Water Pools on the Base
If water sits on your base after rain rather than draining away, your base is probably sitting too low relative to the surrounding ground, or it has a dip in the middle.
You can sometimes fix this by lifting and relaying slabs with a very slight slope away from the shed. A fall of about 1cm per metre is enough to encourage drainage without being noticeable.
Slabs Rock or Move When You Walk on Them
This usually means insufficient sand underneath or poor compaction of the sub-base. Lift the wobbly slab, check the sand bed is even and deep enough (40 to 50mm), and make sure the hardcore below is properly compacted.
If multiple slabs are moving, you might have a bigger problem with the sub-base that needs addressing before you go any further.
Weeds Start Growing Between Slabs
Even with a membrane, determined weeds sometimes find a way through the joints. Pull them out when small rather than letting them establish. You can also brush in a jointing sand that contains a weed inhibitor, or use a path weed killer between the slabs (check it will not damage the slabs themselves first).
Frequently Asked Questions
Do I need planning permission to build a shed on a paving slab base?
In England and Wales, you generally do not need planning permission for a garden shed as long as it is under 2.5 metres tall at the highest point (or 4 metres for a pitched roof shed), does not take up more than 50% of your garden, and is not forward of the principal elevation of your house. Scotland and Northern Ireland have slightly different rules. The base itself does not require permission – it is the shed that matters. If you live in a conservation area or your property is listed, different rules apply and you should check with your local planning authority.
Can I build a paving slab base on a slope?
Yes, but it requires more work. On a slope, you will need to dig significantly deeper on the higher side to create a level platform. This means more excavation, more sub-base material, and potentially building up a retaining edge on the lower side to stop everything sliding downhill. For steep slopes, a concrete base or timber frame base might actually be easier. If the slope is gentle (less than about 1 in 10), a paving slab base is definitely doable with some extra effort.
How thick should paving slabs be for a shed base?
For a typical garden shed, 40mm to 50mm thick slabs work perfectly well. These are strong enough to support the weight without cracking and are the standard thickness you will find at most builder’s merchants. If you are building a base for a very heavy shed, a workshop with lots of equipment, or a garden office where people will be walking around all day, you might want to go for 60mm thick slabs for extra strength. Thicker slabs cost more and are heavier to handle, but they are less likely to crack over time.
Should I use mortar between the paving slabs?
It depends on your preferences. For most shed bases, dry-laid slabs with sand-filled joints work absolutely fine and give you flexibility to lift and relay slabs if needed. Using mortar in the joints creates a more permanent, rigid base that is less likely to shift, but it also means you cannot easily adjust things later. I tend to use a semi-dry sand and cement bed under the slabs and just sand in the joints – it gives you most of the stability without being completely permanent.
How many paving slabs do I need for my shed base?
Calculate the area of your shed base (length times width in metres) and divide by the area of one slab (also in square metres). For example, a 2m by 2m base is 4 square metres. A 600mm by 600mm slab is 0.36 square metres. Divide 4 by 0.36 and you get roughly 11 slabs, though you would round up to 12 to account for any breakages or cuts. Remember to add your 5 to 10cm border around the shed dimensions when calculating the base size. Always buy a couple of extra slabs – they are heavy and prone to cracking if you drop one, and having spares on hand saves another trip to the builder’s merchant.
How long does a paving slab shed base last?
A properly laid paving slab base should last 15 to 20 years or more without needing any major work. You might need to re-level the occasional slab if the ground settles, or top up the sand in the joints now and then, but the base itself is very low maintenance. The key word there is ‘properly laid’ – if you skip steps, particularly on the sub-base, you will start seeing problems within a year or two. Most base failures are down to poor preparation rather than the slabs themselves failing.
Recommended Products
A few products that make this job significantly easier:
Long spirit level (1200mm): Worth buying or borrowing a quality one. A cheap spirit level that is not accurate will make your life miserable. Look for one with both horizontal and vertical vials.
Heavy-duty rubber mallet: Essential for tapping slabs into place without cracking them. Get one that is actually designed for paving work rather than a lightweight DIY mallet.
Landscaping membrane: Invest in a decent quality weed control fabric. The cheap stuff tears easily and does not last. Look for something rated at least 100gsm. For an accurate membrane, consult with landscaping services in Nampa, ID.
Builder’s wheelbarrow: If you do not own one already, this is a good excuse to buy one. Moving sand and hardcore in buckets or bags is exhausting. A wheelbarrow makes everything faster.
Final Thoughts
Building a shed base with paving slabs is one of those jobs that rewards patience and proper preparation. Yes, it is hard work. Yes, it takes longer than you think. But do it properly and you create a foundation that will outlast most sheds.
The secret really is in the sub-base. Spend the time getting that right – digging deep enough, compacting thoroughly, checking for level – and the rest of the job becomes straightforward. Rush the groundwork and you will be fixing problems for years.
Start with realistic expectations about time and effort. A weekend project for an experienced DIYer often turns into a two-weekend job for someone doing it for the first time. That is normal. Budget an extra half day and you will not feel rushed.
And remember that wonky is fixable while you are still building. Once the shed is on top, lifting and relevelling becomes a much bigger job. Take the time to get it right now.
If you are standing in your garden looking at the marked-out area thinking ‘this is a lot of digging’, you are not wrong. It is. But once it is done, it is done properly, and that is a satisfying feeling.
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Becky is the voice behind Life in Velvet, an organised, intentional living blog focused on practical food, calm homes, thoughtful projects, and everyday systems that make real life feel easier. A mum of 3 living in the UK, Becky writes from lived experience, sharing what works, what doesn’t, and the decisions that make family life run more smoothly.
With a background in marketing and content writing, and over a decade of blogging experience, she brings a thoughtful, structured approach to everything from baking and home projects to routines and decision-making. Life in Velvet is where planning meets creativity, with ideas designed for real homes and real life.