For most domestic jobs in the UK, a poured concrete slab costs somewhere between £75 and £130 per square metre once you include digging out, sub-base, formwork and the concrete itself. The spread is wide because the ground under your slab matters as much as the concrete on top. Here is how the numbers actually break down, based on the sort of work we price every week around Luton, Bedfordshire and the West Midlands.
A slab is rarely priced by the bag of cement. Contractors work it out from excavation, muck away, sub-base, shuttering, reinforcement and the volume of ready-mix, then add labour. As a rough guide for a standard 100mm to 150mm domestic slab on decent ground, expect the following all-in figures.
Small jobs cost more per square metre than large ones. Setting up, bringing in a digger and ordering a part load of concrete carries a fixed cost whether you pour 6 square metres or 60, so a small shed base can look expensive for its size while a big garage slab works out better value per metre.
Ground conditions come first. If we dig down and find soft clay, old backfill or tree roots, the dig gets deeper and more sub-base goes in, and that is extra muck away and extra stone. Around parts of Bedfordshire the clay soils shrink and swell with the seasons, which is exactly why a proper compacted sub-base of MOT Type 1 matters more than an extra 20mm of concrete.
Access is the second big one. If a ready-mix lorry can discharge straight into the formwork, you pour fast and cheap. If everything has to go through a house or up a narrow side passage by barrow or pump, labour time climbs and a concrete pump alone can add £300 to £600 to the day. Spec is the third factor: a plain shed base is one thing, but an extension slab needs a damp proof membrane, insulation and usually mesh reinforcement, all signed off by building control, and that pushes the price per metre up.
On a straightforward job, materials and labour split fairly evenly. Ready-mix concrete currently costs in the region of £110 to £150 per cubic metre delivered, and a 150mm slab uses one cubic metre for every 6.5 square metres or so. MOT Type 1 sub-base, membrane, mesh and timber for shuttering add more, and skip or grab hire for the spoil is often the cost people forget, easily £250 to £400 per load.
Labour covers setting out, digging, compacting the stone in layers, building level formwork, placing and tamping the concrete, then finishing the surface. A slab that is poured quickly but finished badly will hold water or crack early, so a decent contractor budgets proper time for compaction and curing rather than racing off site the same afternoon.
Ask any contractor to itemise the dig depth, sub-base thickness, concrete grade and what happens to the spoil. A quote that just says slab supplied and laid tells you nothing, and the cheapest number usually means a shallow dig and thin stone, which is where cracked and sunken slabs come from a couple of years later.
It is also worth asking who is responsible if the ground turns out worse than expected. A fair approach is a fixed price for the expected spec with an agreed rate for any extra dig or stone, confirmed with photos before more concrete is ordered. And if your slab supports a habitable extension, check the design meets building regulations before anyone books a lorry, because rectifying an unapproved slab costs far more than doing it properly the first time.
For sheds and light garden buildings, 100mm over 100mm of compacted sub-base is usually enough. Garage bases and anywhere a vehicle sits should be 150mm, often with mesh reinforcement, and extension slabs are built to whatever the structural design and building control require.
For a small shed base with good access, a competent DIYer can manage it and save a few hundred pounds. Anything involving vehicles, deep dig-outs, pumped concrete or building regulations is worth pricing with a groundworks contractor, because mistakes in the sub-base cannot be fixed once the concrete is down.
You can usually walk on it after 24 to 48 hours, build a shed on it after about a week, and drive on it after 7 to 10 days. Concrete keeps gaining strength for around 28 days, so keep heavy loads and point loads off it for as long as you reasonably can.
Tell us about your job and we will get back to you with a clear, no-obligation quote.