Concrete bases
Garden room and garage bases
Bought a garden room or a garage and been told to have the base ready before it arrives? That is the part we do. A concrete base, dug out to firm ground, level, square and built to the size on the maker's drawing.
Why the base matters more than the building
Every garden room company in Southport will tell you the same thing: have a flat, level base ready before delivery. Very few of them say what that means, or who should build it.
If the base is out of level, the doors stick and the windows will not close. If one corner sinks, the walls twist and the building's warranty can be at risk. If the ground underneath was soft, the whole thing moves.
Getting it right is groundwork: digging out, compacting, setting levels and laying concrete. It is what we do every day on extensions and driveways, just smaller.
Ask the maker for their base drawing
Before we quote, get the base drawing or fitting guide from whoever is making your building. It gives the exact size, and says whether they want the base bigger or a little smaller than the building. We build to that, so their fitters can get straight on.
What we lay bases for
Garden rooms and garden offices
Insulated timber, SIP or steel framed rooms used all year round. Most makers send a base drawing with the exact size they want.
Log cabins and summer houses
Heavy timber buildings that need a flat, level base so the doors and windows open and close properly for years.
Concrete panel and sectional garages
Garage makers are fussy about the base: size, level and how square it is. We build it to their sheet so the panels go up first time.
Timber and steel garages, workshops and carports
A slab strong enough to park on and work on, with the edge where the maker wants it.
Building a brick or block garage? That needs proper footings, the same as a small extension. See extension foundations.
Garden room base options
There is more than one way to do it. Most of the bases we lay are concrete, but we do ground screws and timber bases too. Here is an honest comparison so you can choose.
| Base | Good for | Watch out for |
|---|---|---|
| Concrete slab | Lasts, takes any weight, doubles as the floor of a garage or workshop. What most garage makers ask for. | Needs digging out and a wagon of concrete, so access matters. It is permanent. |
| Ground screws | Big steel screws wound into the ground, no concrete. Quick, little digging, can come out again. | Suit some garden rooms, not garages. Can struggle in very loose sand or ground full of rubble. |
| Timber frame on pads | A frame of treated timber sitting on small concrete pads. Light and good on a gentle slope. | Only as good as the timber and the pads under it. Not for heavy buildings or garages. |
| Plastic grids or slabs | Cheap, quick, fine for a small shed. | Not meant for a garden room you will sit in all year, or for anything heavy. |
Whatever you pick, check with the company making the building first. Some only guarantee their building on the base they ask for.
What goes into a concrete base
The concrete on top is the last layer and the only one you see. These are the layers that stop it sinking, cracking or letting damp through.
- 1
Dug out to firm ground
Turf, topsoil and any soft or made up ground comes out. Around Southport that is often sand; inland it is more often clay. Either way we dig until the ground underneath is firm.
- 2
Compacted stone
A layer of crushed stone, called Type 1, spread and rolled down hard with a compactor. This is what stops the base sinking at one corner.
- 3
Sand blinding
A thin layer of sand over the stone so nothing sharp pokes through the membrane.
- 4
Damp proof membrane
A heavy plastic sheet under the concrete so damp from the ground does not come up through the floor of your building.
- 5
Steel mesh
Reinforcement set in the concrete to hold it together and stop cracks opening up.
- 6
Concrete, level and square
Poured inside timber edges set to the exact size, then levelled and finished. We check it is square by measuring corner to corner both ways: the two numbers should match.
Plan the electric, water and drains before the pour
Most garden rooms need power, some need water, and a few have a toilet or sink. Once the concrete is down, getting a cable or pipe up through the floor means breaking it out.
So tell us early, and we put it all in while the digger is already there:
- A duct for the electric cable, ready for your electrician to pull the cable through and connect it
- A water pipe, ready for your plumber to connect
- The drain pipe for a toilet or sink, back to your house drain or the sewer
Each one comes up through the base exactly where your electrician or plumber wants it.
Sloping gardens
We dig the high side down, build the low side up, or both. On a steep slope the base may need a retaining edge.
One thing to check: if the base ends up more than 30 cm off the ground, it can count as a raised platform, which can mean the garden room needs planning permission. Check with your council first.
Tight access is normal
Most back gardens round here only have a side gate. We use a 1 tonne micro digger and small tracked dumpers that fit through it, then load the soil onto our own grab lorry on the road.
Old shed or concrete garage in the way? We take it down and take it away first.
We are an Environment Agency upper-tier waste carrier, so the soil, the old building and any old concrete go away legally, with the paperwork.
What to tell us when you ring
- The base drawing or fitting guide from whoever is supplying the building. It gives the size they want, and whether the base should be bigger or a little smaller than the building
- Where in the garden it is going, and roughly how far from the fences
- How we get in: the width of the side gate or passage, or whether we can come through a back lane
- Whether it will need electric, water or a toilet or sink, so the pipes and ducts can be planned before the pour
- Anything already there: an old shed or garage, a slab, a patio or tree roots
How we lay a garden room base
The pour itself takes a few hours. The work before it is what makes the base last.
- 1
Look and quote
We come and look at the spot, the ground and the access, check the maker's base drawing, and give you a written price.
- 2
Mark out
The base is pegged out to the exact size, the right distance from the fences and the house, with the level set.
- 3
Dig out
A 1 tonne micro digger comes through the side gate if it has to. The soil goes out on tracked dumpers to our grab lorry on the road.
- 4
Stone and compact
Type 1 stone goes in and is compacted in layers until it is firm and flat.
- 5
Edges, membrane and steel
Timber edges set to size, level and square. Sand blinding, the damp proof membrane and the steel mesh go in, along with any ducts or pipes that need to come up through the floor.
- 6
Pour and finish
The concrete is placed, levelled and finished smooth or brushed, whichever suits the building.
- 7
Leave it to cure
Concrete needs time to get its strength. We tell you when the base is ready for the building to go on, and we protect it from frost or hot sun if the weather needs it.
Planning and building regulations
Most garden rooms do not need planning permission. They usually count as permitted development if they sit behind the house, are single storey, are no more than 2.5 m high when within 2 m of a fence, and do not cover more than half the garden with your other outbuildings.
Conservation areas, listed buildings, flats and anything used as a bedroom have different rules. There are a lot of conservation areas in Southport, so check with your council before you order the building.
Building regulations, roughly
- Under 15 m² with nobody sleeping in it: usually exempt
- 15 to 30 m²: usually exempt if it is at least 1 m from the boundary, or built mostly from materials that do not burn
- Over 30 m², or used for sleeping: needs approval
- A toilet, sink or shower needs its drains done properly whatever the size
Garden room and garage companies
Need a base contractor for your customers around Southport and the North West? We build to your base drawing, with the ducts and pipes where your fitters want them, and the base ready for the day your building arrives. Ring us to talk about it.
Questions people ask
What is the best base for a garden room?
For most garden rooms, a concrete slab is the one that lasts longest and takes any weight. Ground screws are a good choice for some lighter rooms where digging is hard. We lay all three: concrete, ground screws and timber bases. Always ask the company making the building first. Some only guarantee their building on the base they specify.
How much does a garden room base cost?
It depends on the size, how much has to be dug out, what the ground is like, how far the soil and concrete have to be carried, and whether an old shed or slab has to come out first. A base at the end of a long garden with a narrow side gate costs more than one by the back door. We give you a written price after we have seen it.
How thick should a garden room base be?
Whatever the building's maker asks for. Their fitting guide usually says. A garage that a car will be parked in needs more than a garden office. If the maker does not say, we tell you what we would lay and why.
Should the base be bigger than the garden room?
It depends on the building. Some makers want the base a touch smaller, so rain drips off the cladding onto the ground instead of running under the walls. Others want it bigger to give a step or a path. Send us their drawing and we build it to that.
Can you lay a base in a garden with no side access?
Usually, yes. A 1 tonne micro digger and small tracked dumpers fit through most side gates, and our smallest dumper is about 70 cm wide, narrow enough for a standard doorway. The concrete then comes through the same way. If there is a back lane, that is often easier.
My garden slopes. Can you still put a base in?
Yes. We either dig the high side down or build the low side up, or a bit of both. If the base would end up more than 30 cm above the ground, check with your council first: a raised platform over that height can take a garden room out of permitted development.
Do I need planning permission for a garden room?
Often not. Most garden rooms count as permitted development if they are behind the house, single storey, no more than 2.5 m high within 2 m of a boundary, and together with other outbuildings cover less than half the garden. Conservation areas, listed buildings and rooms used for sleeping are different. Check with your council before you order.
Does a garden room need building regulations?
Usually not if it is under 15 m² and nobody sleeps in it. Between 15 and 30 m² it is usually exempt if it is at least 1 m from the boundary or built mostly from materials that do not burn. Over 30 m², or with a bedroom, it does. A toilet or shower always needs the drains done properly.
Can you put the drains in for a toilet or sink in the garden room?
Yes. We lay the drain pipe from the garden room back to your house drain or the sewer while the digger is on site, before the base is poured.
What about the electric and water?
We lay a duct for the electric cable and the water pipe in the same trench, coming up through the base exactly where they are needed. Your electrician then pulls the cable through and connects it, and your plumber does the same with the water. That way nobody has to break the new base out later.
Can you take away my old shed or concrete garage?
Yes. We take down old sheds and concrete garages, break out the old base and take it all away on our grab lorries. We are an Environment Agency upper-tier waste carrier, so it goes away legally, with the paperwork. Older concrete garage roofs were often made with asbestos cement, so if yours might be, it gets checked before anything comes down.
How long before the building can go on?
You can walk on new concrete after a day or two. How long before the building goes on depends on the weather and how heavy it is, so we tell you on the day, and you can pass it on to whoever is fitting the building.
Also worth a look
Send us your base drawing
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