Basement contractors in London. We design, engineer and build basements under one contract. Basement cost in London, the 2026 figures.
A basement creates valuable space. It also places major structural and waterproofing responsibility beneath an existing home. That responsibility sits beside neighbouring properties too. The appointment should therefore be based on evidence, technical control and clarity. It should not rest on a headline excavation rate.
After sixteen years working on London homes, NU Projects recommends ten questions. These are the ones to ask before choosing a basement contractor.
1. Have you completed comparable basements?
Ask for projects matching the property type, excavation method, depth, access and intended fit-out. A simple cellar refurbishment is not the same as a new basement. That applies beneath a period townhouse.
2. Who owns the design responsibility?
Identify who coordinates planning, permanent structure, temporary works, waterproofing, drainage, MEP and interiors. Responsibility must be named and documented.
3. What surveys and investigations are required?
The answer may include measured, structural, drainage, ground, groundwater, tree and utility information. Ask how uncertainty will be reduced before construction.
4. What is the planning strategy?
The team should understand the local authority’s basement policy. It should know the property constraints and likely supporting documents. National basement planning guidance is only a starting point.
5. How will the building and neighbours be protected?
Ask for the excavation sequence, propping, and underpinning or piling method. Ask also for the movement-monitoring plan and hold points for inspection. Understand how party-wall requirements and neighbour communication will be managed.
6. What waterproofing and drainage system is proposed?
The answer should cover design rationale, junctions, penetrations and maintainability. It should cover pumps, alarms, power resilience and access for servicing. A product name alone is not enough.
7. How are ventilation and building services coordinated?
Below-ground rooms need carefully designed air quality, heating, cooling, drainage, lighting and controls. A pool, gym, cinema, wine room or bedroom suite creates different environmental demands.
8. What does the price include and exclude?
Compare investigations, design, approvals, temporary works and excavation. Compare structure, waterproofing, MEP, fit-out and specialist rooms. Compare preliminaries, professional fees, contingency and VAT. Large unexplained allowances are a warning sign.
9. How will changes and progress be reported?
Variations should be described, costed and approved in writing before work proceeds. Progress reporting should connect design decisions, procurement, programme, risk and commercial status.
10. What happens at commissioning and aftercare?
Ask how pumps, alarms and drainage will be tested, documented and maintained. Ask the same of ventilation, heating and controls. Confirm warranties, handover information, defects procedures and the response if a system needs attention.
The evidence checklist
- Comparable completed basement projects
- Named engineer and design responsibilities
- Property-specific surveys and planning route
- Written temporary-works and monitoring approach
- Coordinated waterproofing, drainage and MEP design
- Transparent cost plan and programme
- Documented testing, handover and aftercare
Review the NU Projects portfolio. Ask for the technical story behind the finished photographs.
See the South Kensington triple-basement project. It is a completed example of NU Projects’ residential delivery.
Frequently asked questions
Should I appoint the lowest basement quote?
Only after confirming that every bidder has priced the same design and responsibilities. They must have priced the same temporary works, waterproofing, services and fit-out. The allowances and exclusions must match too.
When should a basement contractor join the design?
Early enough for buildability, logistics and temporary works to influence the scheme. Waterproofing, programme and cost should influence it too.
Can NU manage the complete project?
Yes. NU can coordinate feasibility, architecture, consultants, cost planning, construction, fit-out, commissioning and aftercare.
Ask us the difficult questions
Book a confidential basement consultation with NU Projects before committing to design or construction.
This is the work we do. Basement contractors in London, or ask for a cost estimate.
Published 25 July 2025. Written by the NU Projects studio, edited since for house style and accuracy.