There is no official ranking of London basement companies. Depth, ground, access and approvals differ on every job. A list of names therefore tells a buyer very little. What helps is knowing which questions separate a safe appointment from a risky one.
NU Projects builds residential basements in London. We carry the design, the cost plan, the construction and the building services. Below are ten questions to ask any basement company. Each one says what a full answer sounds like.
Why two basement quotes rarely compare
Two prices can look close and cover different work. One may include surveys, temporary works, waterproofing design and commissioning. Another may leave those with you as provisional sums. Ask every company to price the same written brief. Ask each one to list what it has left out.
Ten questions to ask before you appoint
1. Who holds the structural design responsibility?
Ask for a role and a stage, not a department. A good answer names the engineer and the stage they are appointed to. It also says who checks the design and who signs it off.
2. Who designs the waterproofing, and who stands behind it?
Waterproofing is a system, not a product. A good answer covers the structure, the joints, the drainage and the alarms. It names the designer, the installer and the length of the warranty.
3. What does the temporary works design cover?
Underpinning sequence, propping, shoring and site access all sit here. A good answer describes the sequence for your own house. A weak answer offers a method copied from another job.
4. How will movement be monitored?
Ask what is measured, how often, and by whom. Ask what the trigger levels are. Ask what happens on site once a trigger is reached.
5. What is the party wall position?
Most London basements need party wall awards. Ask who serves the notices and who pays the neighbouring surveyors. Ask how long the awards are expected to take.
6. How are groundwater and drainage handled?
Ask about the water table, the pumps and the power supply to them. Ask what happens in a power cut. Ask who maintains the pumps after handover.
7. What is fixed in the price, and what is not?
Ask for the cost plan split by element. Ask which lines are provisional sums. Ask how a change is priced once work has started. Our build cost calculator gives an early benchmark before any of that.
8. How are the services routed under a low ceiling?
Ventilation, heating, cooling, lighting and drainage compete for the same depth. Ask at which stage the services are coordinated. Early MEP coordination protects the ceiling height you were shown.
9. What does the programme assume about approvals?
Ask which dates depend on planning, building control or a party wall award. Ask what the programme does if one of them slips. A programme that shows site works alone is not a programme.
10. What happens the day after handover?
Ask for the certificates, the manuals and the maintenance schedule. Ask who answers the phone in month nine. Ask how the defects period works and what it covers.
Reading the answers you get back
Write the ten answers down side by side. A company that answers in specifics has done the thinking. A company that answers in adjectives has not. Where two answers differ, ask both firms why. The reason is usually a difference in scope. That difference is the thing you are really comparing.
How NU Projects runs a basement job
NU can carry feasibility, design, cost planning, basement construction, fit out and aftercare under one contract. One team is then accountable for the structure, the waterproofing and the services. Completed work is on our projects pages.
Frequently asked questions
Should the builder be involved before the design is finished?
Yes. Structure, access, waterproofing and services have to be coordinated before anyone digs. Late contractor input is where cost and delay come from.
Is the cheapest basement quote the safest one?
Only if every quote prices the same design, surveys and risks. Otherwise the gap is scope, not value.
How long does a London basement take?
It depends on approvals, ground and size. Ask for a programme that starts at the first survey and ends at handover.
Talk to us about your basement
Two lines about your house is enough to start. Book a consultation with NU Projects before the design and the risk are fixed.
Published 19 October 2025. Written by the NU Projects studio, edited since for house style and accuracy.