Building a shed base with foundation blocks is popular for one simple reason: it feels doable. You don’t have to dig out big trenches or hire a cement mixer and wait weeks for the base to set. Foundation blocks are cheap and easy enough for even beginner DIYers to use confidently. 

However, that’s not to say you can cut corners or not pay attention to detail when installing it. You still need to build it properly if it’s going to support your shed. If you use the wrong blocks, don’t level or space them properly or make sure they’re on the right sub base, you are going to end up with a shed that eventually sinks or twists out of shape (yes, twisting is a real thing that happens). 

This guide is going to keep things simple so you can make sure you lay them properly from the start. You’ll learn which blocks are the best to use, how to avoid common mistakes that can lead to expensive problems and the steps you need to follow to make sure your foundation blocks sit and stay for years to come. 

What’s the difference between pier blocks, concrete blocks, breeze blocks, cinder blocks, and deck blocks?

If you’ve ever done a search for foundation blocks, you’ve probably seen a number of terms used interchangeably when in fact they do refer to different things. This quick comparison table should clear up any confusion so you know exactly which blocks belong underneath your garden shed and which ones are best avoided. 

Block type	What it is	When it works well	When it doesn’t work
Concrete blocks	Dense heavy blocks made from solid concrete. They’re very strong	Most shed bases, uneven ground, supporting timber frames	Too heavy for soft, clay or very wet ground without a proper gravel base beneath
Deck blocks	Precast blocks with built-in grooves for timber joists. They are designed for smaller structures	Beginners, lightweight sheds, flat gardens, fast installs	Not ideal for heavy sheds as they can wobble if the ground beneath isn’t compacted properly
Pier blocks	Taller, narrower blocks that lift the shed further off the ground. These can be used to correct small slopes in your garden	Gardens with a slight slope, wet gardens where you need to raise the shed off the damp ground. These are great for shed ventilation	Not suitable for large or heavy sheds unless they have extra support
Breeze blocks	Hollow concrete blocks that are weaker when laid sideways	Not a great choice for a shed base	They can crack and crumble, especially when laid sideways under load bearing points
Cinder blocks	The US term for breeze blocks	Not a great choice for a shed base	They can crack and crumble, especially when laid sideways under load bearing points

Important note: Hollow blocks (breeze/cinder blocks) often show up in DIY videos but they’re not designed to support concentrated weight. For shed bases, always choose solid concrete, deck blocks or pier blocks, depending on your ground and shed size.

If you’re putting in the effort to get the base right, it’s worth choosing a shed that’s built properly too. Explore our durable garden sheds designed for long-term stability →

What are the best blocks to use for a shed base?

There are plenty of block types sold in DIY stores, but only a handful are actually suitable for supporting a shed long-term. Here are the top picks:

1. Solid concrete blocks (best overall)

• Strong enough for most shed sizes
• Affordable and easy to source
• Simple to level with gravel underneath
• Cope well with slightly uneven ground when spaced properly

2. Deck blocks (best for beginners)

• Drop your timber joists straight into the grooves
• Quick to set out and adjust
• Ideal for lightweight sheds, bike stores and small workshops
• Great choice when you want a fuss-free install

3. Pier blocks (best for slopes/wet gardens)

• Lift the shed higher off the ground for airflow
• Useful for gardens with slight gradients
• Keep the base clear of standing water
• Help create a level platform without major digging

4. Blocks to avoid

• Hollow cinder/breeze blocks used sideways
• Decorative blocks with low load strength
• Any block placed directly on soil without a gravel sub-base

The benefits of concrete blocks for a shed base

• Affordable compared to slabs or concrete

Blocks give you solid support without the cost of formwork, materials or the labour that a full slab demands. You can build a strong and steady base for a fraction of the price which helps to keep the overall cost of your garden shed project down.

• Easy to install without specialist tools

All you need is a shovel, level, gravel and a free afternoon. No curing time and no heavy machinery because this is a straightforward DIY setup.

• Works on sloped or uneven ground

Because each block can be adjusted individually, you can correct small height differences without major digging. This makes block bases a good fit for gardens that aren’t ever really perfectly flat.

• Allows great airflow

Raising the shed off the ground prevents moisture building up under the floor. Better airflow means a drier shed with no rot and a longer lifespan for the timber.

• Ideal for timber frame bases

The flat, solid surface of a block is perfect for supporting a timber frame and gives you clear anchor points for fixing the frame securely.

• Not permanent

If you ever want to move or upgrade your shed, you can just lift the blocks and move them elsewhere because nothing is fixed to the ground.

• Can be adjusted later if the shed moves

Ground can move after storms or just from natural settling over time. Using blocks for a shed base makes it easy to re-level the shed without rebuilding the whole foundation.

• DIY-friendly for small to medium sheds

You don’t have to have more than basic DIY knowledge and skill to lay a shed base made of foundation blocks. 

The problems with concrete blocks for a shed base

• Concrete blocks can shift or settle on soft ground which means the shed can slowly lean or sag unless the blocks sit on a compacted gravel pad.
• Sheds built on blocks in windy areas need to be anchored properly as there is a risk of uplift during storms 
• The freeze–thaw cycles in the UK can cause minor movement each winter which leads to gradual misalignment and the need to re-level the blocks every few years, particularly in colder regions to the North, Scotland and the Midlands.
• Blocks don’t stop weeds or grass growing underneath the shed, so the area can stay damp and prone to mould unless you use a membrane and gravel base to keep vegetation down and moisture away and if you don’t use proper weed protection, you may also end up scuffing the wood on your shed when trying to mow around it.
• Foundation blocks do not help to keep your shed walls clean. Heavy rain splashes mud up onto shed walls which can lead to rot over time from the moisture. It’s always best to use a gravel pad slightly bigger than your shed to account for this.
• Raised block bases create sheltered gaps that attract rodents and other small animals, which may chew your insulation and wiring or even parts of the shed floor unless the space is managed properly.
• A block base only works if the blocks are perfectly level and correctly spaced out. 

If you’d rather not deal with sagging floors or re-levelling jobs every few years, it’s a good idea to choose a shed that’s built to cope with UK weather from day one. 

Explore our long-lasting garden sheds →

Important considerations if you choose shed foundation blocks

• Planning permission usually isn’t needed for most garden sheds but you must keep the finished height under 30cm or it may count as a raised platform which can trigger planning rules in the UK.
• Foundation blocks are not just a perimeter support. You must place them underneath the centre of the shed as well as the corners because a shed supported only around the edges will develop a soft, bouncy floor and eventually sag in the middle.
• You’ll still need a proper shed base sitting on top of the blocks (usually a timber frame) because foundation blocks alone don’t provide enough continuous support for the floor panels.
• It really is a good idea to put a gravel pad underneath to help with drainage so you don’t get moisture damage.
• Diagonal alignment matters more than most beginner DIYers realise, so be sure to check both diagonals match and are level before installing your shed otherwise the shed may lean or twist even if the ground itself is level.

Tools and materials for a concrete block shed base

Here’s what you need to lay a shed base made of foundation blocks:

Materials:

• Solid concrete blocks / deck blocks / pier blocks
• 20 mm gravel
• Weed membrane
• Timber joists (UC4 treated)
• Damp-proof membrane 
• Metal brackets or L-braces
• Ground anchors
• Plastic shims (optional)
• Anti-weed jointing sand (optional)
• Guttering kit if the base extends beyond the shed footprint (optional)

Tools:

• Spirit level
• Timber straightedge
• Stakes and string
• Tape measure
• Shovel
• Rake
• Hand tamper or plate compactor (either works)
• Saw (if cutting timber joists)
• Drill/driver
• Hammer or mallet

How to build a shed foundation with concrete blocks step by step

Follow these steps to get a perfectly level, strong shed base using foundation blocks:

1. Plan your block layout

Start by marking out where your garden shed will sit and add an additional 5 to 10 cm margin around the edges. Once the footprint is outlined, you can decide how many blocks you will actually need. Small sheds might only need six blocks, medium sheds often take around nine to twelve and anything heavier will need more support to stop the floor from dipping. The idea is simply to picture where the weight will land and make sure there’s a block under every load-bearing point.

2. Clear and level the area

Next, strip the whole area so you’re working on a clean, flat surface. Lift the turf, pull out any weeds, remove roots or stones and anything else that could create a soft spot later. Give the soil a good rake and pat it down a little so it’s not fluffy. You don’t need it compacted like concrete at this stage but it needs to be firm so you can check that it’s level.

3. Lay a weed membrane + gravel pad

Once the area is clear, roll out a weed membrane to stop grass and weeds creeping up underneath the shed. Then add a shallow layer of gravel about 50 to 75 millimetres deep and spread it evenly. Compact it using a tamper and then check everything with a long straightedge or board to make sure you haven’t created any little hills or troughs.

4. Position your blocks

Now you can start laying the blocks themselves. Most people begin with the corners because they act as your reference points. When they’re set, add the midpoint blocks along the sides, then drop the centre blocks into place. Keep an eye on the height as you go because even a few millimetres difference can cause a wobble later. Check the diagonals, adjust anything that looks off and use plastic shims under a block if you need to lift it slightly without moving the whole pad. It’s best to take your time and be absolutely sure your blocks are level before proceeding. This step is the one that determines the stability of your shed and how well it will hold.

5. Build and position the timber frame

Lay your timber frame on top of the foundation blocks and make sure every corner and centre point is supported. The frame should sit fully on the blocks without any floating edges or bits of the frame unsupported. Treat any cut ends before they go near the ground, and double-check the diagonals of the frame itself to make sure it’s square. Once everything sits flat and steady, you’re ready to move on.

6. Anchor everything

Make sure everything is anchored properly. You can use ground anchors, straps or simple L-brackets depending on the design of the shed and your garden. This part is particularly important in exposed or windy locations because an unanchored shed can shift or even lift up during bad weather. This is also just a smart extra step to make sure your whole build is extra secure.

7. Place your shed on top

Now position your shed on the frame and make sure it sits evenly all the way around. Once you’re sure it’s all steady and even, fix it down according to the manufacturer’s instructions.

Last Thoughts

A block foundation can be a brilliant way to support your garden shed as long as you take the time to set it up properly. When the blocks are level, the gravel is compacted and the frame is supported in all the right places, you end up with a base that’s sturdy, well-ventilated and easy to maintain. And if the shed does ever settle a little over the years, you can adjust individual blocks without tearing the whole thing apart, so this is a great option for most UK homeowners.

Like most garden projects, the details matter in ensuring your base is a success. A few extra minutes spent checking levels, spacing the blocks correctly and anchoring everything down will save you a lot of frustration later. Once the base is in place though, you’ll have a solid platform that keeps the shed dry and ready for whatever you need to store in it.

Want a shed that will do justice to the base you’ve just put in? 

Browse our range of sturdy, weather-ready garden sheds that sit beautifully on a block foundation →

Frequently asked questions

1. How many pier blocks for a shed foundation

It depends on the size and weight of the shed. A small shed might only need six pier blocks, but most medium-sized sheds need closer to nine or twelve to support the centre as well as the corners. Larger or heavier buildings need additional blocks along the load-bearing points so the floor doesn’t sag. The safest approach is to support every major joist line on your shed design, not just the edges.

2. Can I use concrete blocks instead of a concrete slab?

Yes, concrete blocks are a perfectly workable alternative for many sheds. As long as they’re solid blocks (not hollow) and they sit on a compacted gravel pad rather than bare soil, they can create a perfectly stable base. A slab is still better for very large or very heavy structures but for most garden sheds, blocks do the job well if they’re laid correctly.

3. Do concrete blocks make a good foundation for a shed?

They do, provided you use the right type of block and prepare the ground properly. Solid concrete blocks can carry significant weight, allow good airflow underneath the shed, can be levelled easily and are cost effective. They’re also adjustable later if the ground settles. Problems only arise when blocks are spaced incorrectly or placed directly on soft soil.

4. Should blocks go under the shed corners only?

Definitely not. Supporting only the corners is one of the main reasons shed floors end up bouncy or sagging. The centre of the shed carries more weight than most people realise, especially once tools, bikes or shelving are added. Always support the middle of the shed with additional blocks so the load is distributed evenly.

5. Can I put blocks directly on soil?

You should never do this with any shed base, not just foundation blocks. Soil moves with rain, frost and seasonal changes and blocks placed straight on top will just move right along with it. A compacted gravel pad is essential because it drains well and keeps the base stable.

6. Can a shed on blocks blow over?

It can if it isn’t anchored down and your garden is exposed to high winds. Because block bases raise the shed slightly off the ground, they don’t offer any built-in resistance against uplift from wind. Using ground anchors, straps or brackets will keep the shed stable even in rough and stormy weather.