Foundations, drainage and site preparation
Groundworks
Groundworks cover the below-ground and site-preparation stage of a build — excavation, foundations, drainage and hardstanding sub-base — carried out before structural building work begins.
Definition
What groundworks involves
Groundworks are the first physical stage of most construction projects: clearing and levelling the site, excavating and pouring foundations, laying drainage runs, and preparing sub-base for driveways, patios or slabs. Ground conditions found during excavation can affect foundation design, which is why groundworks are usually priced with provisional allowances until the ground is opened up.
Suitable for
- Foundations for extensions, new builds and outbuildings
- Drainage installation as part of a wider project
- Site clearance and levelling ahead of construction
- Sub-base preparation for driveways, patios or hardstanding
Not suitable for
- Groundworks without a structural engineer's foundation design already confirmed — we coordinate this as part of the wider project rather than starting excavation without it
Process
How the work is carried out
- 01
Site survey
Assessing existing ground conditions, services and access ahead of work starting.
- 02
Clearance
Clearing vegetation, existing hardstanding or structures as needed.
- 03
Excavation
Excavating to the depth specified by the foundation design, adjusted if ground conditions differ from expected.
- 04
Foundations and drainage
Pouring foundations and laying drainage runs to specification.
- 05
Backfill and compaction
Backfilling and compacting ready for the structural build to begin.
Typical timescale
Groundworks for a typical extension take one to two weeks; larger new-build groundworks take longer and depend on ground conditions found on excavation.
Cost guidance
Cost depends on ground conditions, excavation depth and access. Provisional sums are standard practice for groundworks since conditions below ground can't be confirmed until excavation starts.
Limitations and exclusions
- Foundation design is provided by a qualified structural engineer, not written in-house
- Unexpected ground conditions (e.g. unsuitable soil, buried services, contaminated ground) are priced as variations once identified
- Services connections (water, gas, electric) beyond the immediate excavation are coordinated with the relevant utility
Areas we cover
Groundworks across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for groundworks in each town we work in.
Evidence
Related projects
Related services
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FAQs
Groundworks FAQs
Why are groundworks often priced with provisional sums?
Ground conditions can't be fully confirmed until excavation begins — unexpected soil conditions, tree roots or buried services can affect the work. Provisional sums keep the quotation honest rather than guessing at conditions we can't yet see.
Discuss your groundworks project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-19.