HOW TO HIRE · TRADES & CONSTRUCTION

How to hire an extension builder in the UK
The checks, the questions and the paperwork.

An extension needs building regulations approval or a Scottish warrant, and often party wall notice. The checks, the questions and the paperwork for a sale.

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THE 60-SECOND VERSION

Hiring an extension builder in five steps

  1. Sort planning and building regulationsTwo different approvals; you might need both.
  2. Get drawings and a specificationEvery extension builder prices the same thing.
  3. Serve party wall notice in timeIn England and Wales, before work near a shared wall or boundary.
  4. Agree stage paymentsFoundations, walls, roof, first fix, completion.
  5. Get the completion certificateFrom building control, or the accepted completion certificate in Scotland.

BEFORE YOU BOOK

Check before you book

No register applies

No law licenses extension builders in England, Wales, Scotland or Northern Ireland; for the extension build the law controls the work itself, through building regulations approval where it is needed.

Get a clear answer on approval for the extension build, and the reference number if there is one. gov.uk →

Building regulations approval

Extensions are squarely within the Building Regulations 2010, as gov.uk explains, so the extension build needs approval from building control, and planning permission is a separate question. If the extension build is approved on full plans in England, expect building control's completion certificate within about 8 weeks of the finish, as long as it complies. Scotland puts the warrant duty on the owner: if the extension build needs a building warrant and there is none, the council can fine you and order the work taken out, whoever built it. Northern Ireland asks you to notify the council's building control before the extension build begins.

Get the building control reference for the extension build before anything starts. Check the warrant (Scotland) or the building control reference (Northern Ireland) is in place before the extension build. gov.uk →

Party wall notice

Under the Party Wall etc. Act 1996 you must tell neighbours in England and Wales before building work on or near a shared wall or boundary, and the extension build often is; a party wall agreement is separate from building regulations approval. Scotland has different rules.

Agree who serves party wall notice for the extension build, and when. gov.uk →

Who holds the client duties (CDM 2015)

For the extension build on your own home, CDM 2015 does not leave the client duties with you: HSE says they pass to the contractor, or the principal contractor where there are several.

Get the principal contractor for the extension build named in writing. hse.gov.uk →

VAT

An extension to an existing house is standard-rated at 20%; only building a separate new dwelling is zero-rated, and the 5% rate is for converting or renovating a home empty for two years or more, so a builder over the £90,000 threshold should charge 20% and show it on its own line.

Ask for the VAT number, and look for VAT as its own line on the extension contract. gov.uk →

“Who is applying for building regulations approval for the extension build?”

A good answer: A named person and building control body, and a reference before foundations are dug.

“Have you built extensions like this one?”

A good answer: Finished examples of similar size and specification, with a client to call.

“What do the foundations depend on?”

A good answer: Ground conditions and building control's requirements, with how extra depth is priced.

“How will the extension join the house?”

A good answer: The opening, the steel and its temporary support, from a structural engineer's design.

“Who serves party wall notice?”

A good answer: The extension builder, a surveyor or you, agreed before the start date.

“What is the programme for the extension build?”

A good answer: A written programme by stage and how weather delays are handled.

“How will stage payments work?”

A good answer: Payments tied to finished, inspected stages, never a large sum up front.

Getting the quote right

  • Price against the drawings, broken into stages
  • Foundations and any extra depth priced per metre
  • Steel, glazing and roof covering named
  • Building control fees and who pays
  • Who actually attends — the builders and each trade on the extension, employed or subcontracted — and the business's VAT number, with VAT at 20% shown as its own line
  • Provisional sums listed
  • Skip, scaffold and making good the existing house

Walk away if

  • Wants to start before approval or before party wall notice is served
  • A single price with no stages
  • Large cash deposit
  • No structural design for the opening into the house
  • Says building control is 'not needed for this size'
LOW
£1,800
TYPICAL
£2,700
HIGH
£4,000

What an extension builder costs: £1,800–£4,000 per m²

Extensions are priced per square metre as a guide, then as a fixed quote from drawings; specification, storeys, foundations and glazing set the final figure. House Extension price guide →

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

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Extension builders near you, with the badges that matter shown

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  1. ApprovalsPlanning where needed, building regulations approval, party wall notice.
  2. GroundworksFoundations dug, inspected by building control and poured.
  3. ShellWalls to wall plate, roof on, windows in.
  4. Fit-outFirst fix, plaster, second fix, opening into the house formed.
  5. CompletionFinal inspection, completion certificate, snag list closed.

Full plans
A detailed building regulations application approved before work starts.
Building notice
A shorter application for simpler work in England.
Wall plate
The timber on top of the walls that the roof sits on.
Party wall award
The document setting out how work near a shared wall will be done.
Lintel / steel
The beam over a new opening.
Completion certificate
Building control's confirmation that the work complies.

AFTER

When the job is done

File the completion certificateFrom building control, with the approved drawings and the structural calculations; buyers will ask.
Collect the trade certificatesElectrical, gas, glazing and any other specialist certificates.
Agree the snag listIn writing before the final payment.
Review the jobOnly booked jobs can be reviewed on Locufy, so yours carries weight; if the extension build falls short, use the make-it-right step first and the provider is asked to fix it before the review is published.

STEP 1Start with the builder, in writingSend the builder a short, dated account of the problem with the extension build and the fix you want. Section 49 of the Consumer Rights Act 2015 implies reasonable care and skill into the contract, and section 54 gives you repeat performance or a price reduction when it is missing.
STEP 2Use Locufy's make-it-right stepRate the extension build 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 workAn approval that was needed for the extension build and never obtained is taken up by the council: building control in England, Wales and Northern Ireland, or in Scotland the building standards service, which holds the owner responsible for the warrant. For a dispute about the extension build 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 extension build 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 an extension builder: questions people ask

No law licenses builders. The extension build needs building regulations approval, or a building warrant in Scotland, and often planning permission.

A building control completion certificate in England, Wales and Northern Ireland, or an accepted completion certificate in Scotland, plus each specialist trade's certificate.

£1,800–£4,000 per square metre, typically around £2,700. Specification moves it most, then one or two storeys and the ground conditions. The House Extension price guide goes through it line by line; type your postcode above for extension builders in your area.

Possibly; gov.uk says planning and building regulations are different approvals and you might need both.

In England and Wales, under the Party Wall etc. Act 1996 if the work is on or near a shared wall or boundary.

HSE says your client duties pass to the contractor, or the principal contractor if there are several.

MORE GUIDES

More hiring guides in trades & construction

How to hire: BuilderHow to hire: ArchitectHow to hire: Structural EngineerHow to hire: GroundworksHow to hire: General ContractorHow to hire: Concrete & Foundations SpecialistHow to hire: BricklayerHow to hire: Orangery BuilderAll 701 hiring guides →

Extension builders near you

Extension builders in LondonExtension builders in ManchesterExtension builders in BirminghamExtension builders in GlasgowExtension builders in BelfastAll extension builders 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