A groundworker carries out all the below-ground and early-stage construction work that forms the foundations of any building project. On a typical domestic extension they will strip topsoil, excavate foundation trenches, install drainage runs, pour foundation concrete and lay the ground floor slab. Groundworkers operate excavators and other plant as well as working with concrete, drainage pipes and below-DPC masonry. Building Control will inspect the foundations before concrete is poured, so the groundworker must coordinate inspections at the right stage. The trade overlaps with drainage specialists and concrete specialists on larger projects.
What they do
- Site clearance and topsoil stripping
- Foundation excavation - strip, trench fill and pad foundations
- Concrete raft and ground beam installation
- Below-ground drainage installation
- Ground floor slab construction
- Beam and block floor installation
- Retaining wall construction
- Land drainage and soakaway installation
When you need one
A groundworker is typically the first trade on site. Their work must be completed before the bricklayer and structural trades can begin above ground.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Groundworker day rate (labour) | £200 - £350/day |
| Foundation excavation and concrete (per m) | £80 - £200/m |
| Ground floor slab (per sq m) | £80 - £150/sq m |
| Below-ground drainage (per m run) | £50 - £120/m |
| Soakaway installation | £500 - £2,000 |
| Mini-digger hire (with operator) | £300 - £500/day |
Groundworks costs vary significantly with soil conditions, depth and site access. Allow a contingency of 15-20% for groundworks - unexpected soil conditions or underground obstructions are common.
Qualifications to look for
The CSCS Labourer or Skilled Worker card confirms health and safety competence and relevant trade qualifications. Essential on all commercial and larger domestic construction sites.
If the groundworker is operating excavators or other plant machinery, a CPCS card confirms they are trained and competent to operate that category of plant safely.
How to find a reputable groundworker
Frequently asked questions
What does a groundworker do on a new build extension?
On a domestic extension the groundworker strips the topsoil, excavates the foundation trenches to the depth specified by the structural engineer, installs any drainage runs, lays the foundation concrete, builds up the below-DPC masonry or installs a concrete raft, and lays the ground floor slab or beam and block floor. They typically complete their work before the main bricklaying and structural trades begin above ground.
How deep do foundations need to be?
Foundation depth depends on soil type, tree proximity and the load being carried. A typical strip foundation for a single-storey extension on stable clay is around 1 metre deep. On shrinkable clay near trees, foundations may need to be 2.5 metres or deeper. Your structural engineer will specify the depth and the Building Control officer will inspect before concrete is poured.
Do groundworkers lay concrete slabs?
Yes - groundworkers typically lay concrete oversite slabs, garage floors and ground floor slabs for extensions. The slab specification (thickness, reinforcement, DPM and insulation layers) is set by the structural engineer or Building Control and the groundworker installs the layers in sequence and levels the concrete ready for the floor finish.