HOW TO HIRE · TRADES & CONSTRUCTION

How to hire a basement conversion specialist in the UK
The checks, the questions and the paperwork.

Basement work needs building regulations approval or a Scottish warrant, and often party wall notice. The checks, the waterproofing questions and the paperwork.

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THE 60-SECOND VERSION

Hiring a basement conversion specialist in five steps

  1. Get an engineer involvedStructural design for any lowering, underpinning or new openings.
  2. Serve party wall noticeIn England and Wales, excavation near a neighbour's foundations needs it.
  3. Agree the waterproofing systemNamed, with how water is managed and drained.
  4. Check the approvalsBuilding regulations always; planning sometimes.
  5. Keep the guaranteesWaterproofing and structural paperwork, with the completion certificate.

BEFORE YOU BOOK

Check before you book

No register applies

No law licenses basement conversion specialists in England, Wales, Scotland or Northern Ireland; for the basement conversion the law controls the work itself, through building regulations approval where it is needed. Expect public liability cover for the basement conversion, and ask for the insurer's name and the limit. Because you are buying from a trader, the Consumer Rights Act 2015 applies to the basement conversion; agreed in your home or at a distance, it usually carries a 14-day cancellation right under the Consumer Contracts Regulations 2013, although work you asked to begin early is paid for and made-to-measure goods are excluded (regulation 28).

Ask whether the basement conversion needs building regulations approval, and who is applying for it. Have the insurance details in hand before the basement conversion, and check the trader and ID-checked marks on the profile. gov.uk →

Building regulations approval

The basement conversion makes a habitable room below ground, so it needs building regulations approval covering structure, fire escape, ventilation and protection from damp. Under a full plans application in England, building control should issue the completion certificate for the basement conversion within 8 weeks of the work ending, if it meets the regulations.

Have the building control reference for the basement conversion in writing before work starts. gov.uk →

Party wall notice

If the basement conversion touches a shared wall or is close to the boundary in England or Wales, the Party Wall etc. Act 1996 means notifying the neighbours first; this is separate from building regulations, and Scotland follows other rules.

Agree who serves party wall notice for the basement conversion, and when. gov.uk →

Who holds the client duties (CDM 2015)

On a domestic job, HSE explains, the CDM 2015 client duties move to the contractor — or the principal contractor if the basement conversion involves more than one contractor.

Get the principal contractor for the basement conversion named in writing. hse.gov.uk →

VAT

Converting a basement into rooms of your existing home is standard-rated at 20% — the 5% reduced rate applies only if the conversion changes the number of dwellings or the house had stood empty for at least two years — and a firm over the £90,000 threshold must charge it and show it on its own line.

Ask for the VAT number, and look for VAT as its own line on the basement contract and each stage invoice. gov.uk →

“Who designs the basement conversion structure?”

A good answer: A structural engineer, with calculations for underpinning, lowering and openings.

“Which waterproofing system will the basement have?”

A good answer: A named system — cavity drain membrane, tanking or both — with drainage and a pump if needed.

“How will the party wall process be handled?”

A good answer: Notices served in time, a surveyor if needed, and the neighbours' consent or an award.

“How will spoil from the basement dig be removed?”

A good answer: A plan for muck-away and skips, and how the street and neighbours are protected.

“What is the fire escape route from the basement conversion?”

A good answer: A route building control will approve.

“What guarantee covers the waterproofing?”

A good answer: A written guarantee, its length and who backs it.

Getting the quote right

  • Structural design and underpinning
  • Waterproofing system and pumps named
  • Excavation and spoil removal
  • Party wall and building control costs
  • Who actually attends — the site team digging and waterproofing the basement, employed or subcontracted — and the business's VAT number, with VAT at 20% shown as its own line
  • The programme and the stage payments

Walk away if

  • Digs before party wall notice is served
  • No structural engineer
  • Unnamed waterproofing 'system'
  • No plan for water ingress or a pump
  • Large deposit before work
LOW
£30,000
TYPICAL
£75,000
HIGH
£140,000

What a basement conversion specialist costs: £30,000–£140,000 per project

Basement conversions are quoted per project; converting an existing dry cellar is the low end, and digging out or lowering the floor with underpinning costs most. Basement Conversion price guide →

Guide prices compiled by the Locufy team from published Irish and UK provider price lists and 2026/27 cost guides. Updated 2026.

KNOW WHAT TO LOOK FOR? NOW FIND ONE

Basement conversion specialists near you, with the badges that matter shown

ID checked, trader status and one score from every review — on the card, before you message anyone. Nearest first. No account needed to look.

Or post the job free and let them come to you.

  1. Design and approvalsStructural design, building regulations, planning if needed, party wall notices.
  2. Excavation and underpinningGround dug out in sequence, walls underpinned.
  3. StructureSlab, walls and any new openings formed.
  4. Waterproofing and servicesMembrane or tanking, drainage, pump, electrics and ventilation.
  5. Fit-out and completionFinishes, fire escape, final inspection and certificate.

Cavity drain membrane
A studded membrane that lets water drain to a sump.
Tanking
A waterproof coating applied to walls and floor.
Sump and pump
A pit and pump that remove water collected behind the membrane.
Underpinning
Deepening foundations to support the building.
Spoil
Excavated earth taken off site.
Party wall award
The surveyor's document setting out how work near a neighbour will be done.

AFTER

When the job is done

Keep the paperworkCompletion certificate, structural calculations, party wall award and waterproofing guarantee.
Service the pumpIf one was fitted, at the interval the maker sets.
Watch for dampThrough the first wet season.
Review the jobOnly booked jobs can be reviewed on Locufy, so yours carries weight; if the basement conversion falls short, use the make-it-right step first and the provider is asked to fix it before the review is published.

STEP 1Put it to the specialist in writingDescribe the fault with the basement conversion, with photos, and say what would put it right. The Consumer Rights Act 2015 expects a trader to use reasonable care and skill; where that fell short you may require the work to be done again, or a lower price.
STEP 2Use Locufy's make-it-right stepRate the basement conversion under four stars and you are asked whether to send it to the provider first; we follow it through. Then the review goes up.
STEP 3Unapproved or dangerous workIf the basement conversion needed approval and did not get it, the council deals with it: building control in England, Wales and Northern Ireland, or the building standards service in Scotland, where the owner answers for a missing warrant. For a dispute about the basement conversion with the trader, Trading Standards is reached through the Citizens Advice consumer helpline on 0808 223 1133 in England and Wales, Advice Direct Scotland on 0808 800 9060, or Consumerline on 0300 123 6262 in Northern Ireland.
STEP 4Money still in disputeIf the basement conversion is still not settled, you can claim without a solicitor: the small claims track takes claims up to £10,000 in England and Wales, simple procedure up to £5,000 in Scotland, and the small claims court up to £5,000 in Northern Ireland.

Hiring a basement conversion specialist: questions people ask

Yes: building regulations approval, or a building warrant in Scotland; planning sometimes too.

In England and Wales, excavation near a neighbour's foundations is covered by the Party Wall etc. Act 1996.

£30,000–£140,000 a project, typically around £75,000. Digging out or lowering the floor, which needs underpinning, pushes it towards the top. How the figure is built up is in the Basement Conversion price guide; search by postcode above to see what basement conversion specialists near you quote.

HSE says your client duties pass to the principal contractor on a multi-trade job.

No law licenses them; check the structural design, the waterproofing guarantee and insurance.

Months for a dig-out; ask for a written programme.

MORE GUIDES

More hiring guides in trades & construction

How to hire: UnderpinningHow to hire: Structural EngineerHow to hire: GroundworksHow to hire: Damp ProofingHow to hire: ArchitectHow to hire: General ContractorHow to hire: BuilderHow to hire: Concrete & Foundations SpecialistAll 701 hiring guides →

Basement conversion specialists near you

Basement conversion specialists in LondonBasement conversion specialists in ManchesterBasement conversion specialists in BirminghamBasement conversion specialists in GlasgowBasement conversion specialists in BelfastAll basement conversion specialists on Locufy →

Sources — checked October 2026

  1. gov.uk — building regulations approval (England)
  2. gov.uk — building regulations: how to apply
  3. TrustMark — the Government Endorsed Quality Scheme
  4. mygov.scot — if a builder is doing the work for you
  5. nidirect — how to apply for Building Regulations approval
  6. gov.uk — party walls and building work
  7. Party Wall etc. Act 1996
  8. HSE — CDM 2015: domestic clients
  9. HSE — deciding if asbestos work must be done by a licensed contractor
  10. Consumer Rights Act 2015, section 49 — reasonable care and skill
  11. Consumer Rights Act 2015, section 54 — what you can ask for when a service falls short
  12. Consumer Contracts Regulations 2013, regulation 30 — the 14-day cancellation period
  13. Consumer Contracts Regulations 2013, regulation 28 — contracts the cancellation right does not cover
  14. Consumer Contracts Regulations 2013, regulation 36 — services started within the cancellation period
  15. Civil Procedure Rules Part 26 — the small claims track limit (England and Wales)
  16. Scottish Courts and Tribunals — making a claim under simple procedure
  17. nidirect — the small claims process (Northern Ireland)
  18. Buildings and construction (VAT Notice 708) — 2.1 Construction services: work to an existing building is normally standard-rated
  19. GOV.UK — VAT rates
  20. GOV.UK — Register for VAT: when to register