Getting a building quote is easy. Getting three accurate, comparable quotes that reflect the actual scope of work, and then choosing the right one, takes a little more preparation. Homeowners who skip the briefing stage almost always end up with quotes that cannot be meaningfully compared, leading to either an unpleasant surprise mid-project or the wrong contractor being chosen.
Why Most Quote Comparisons Go Wrong
The root problem is almost always an inadequate brief. If three builders are given a vague description of the work (“extend the kitchen into the garden”), each will make their own assumptions about:
- Specification of materials (concrete block vs. timber frame vs. SIPs)
- Quality of finishes (basic vs. mid-range vs. premium)
- What is and is not included (groundworks, drainage, making good, decoration)
- Programme length and therefore labour costs
The result is quotes that might vary by 40–60% not because one builder is cheaper than another, but because they have priced entirely different jobs. The only way to get genuinely comparable quotes is to give every contractor the same written brief.
Step 1: Prepare Your Brief
Before approaching any builder, prepare a written package. For most domestic projects this should include:
Drawings, even a simple sketch with dimensions helps. For anything involving structure or planning permission you will likely have architect or structural engineer drawings already. Share these.
A schedule of works, a numbered list of every item of work you want priced. This does not need to be a formal document; a clear Word document or spreadsheet is fine. The more specific the better:
“Supply and fit new 3m x 2m bathroom with customer-supplied sanitaryware, contractor to supply and tile with customer-approved ceramic tiles up to 1.8m, install extractor fan to Building Regs Part F requirements, new shaver supply unit, electrical certificate on completion.”
Where a regulation gives a figure, put it in the schedule. Approved Document F, for example, sets a minimum intermittent extract rate of 15 litres per second for a bathroom.1
Specification notes, where the contractor is supplying materials, state the quality level (e.g. “mid-range engineered oak flooring, minimum 14mm wear layer” or “standard sand/cement render to external walls, painted finish”).
Programme requirements, your preferred start date and any constraints (you need the kitchen functional by a certain date, you are away for two weeks in August).
Access and site conditions, parking availability, hours of access, any complications (party walls, listed building consent, asbestos survey results).
Step 2: Who to Approach
Get a minimum of three quotes.2 More than five rarely adds value and wastes everyone’s time.
Sources of reputable builders:
- Personal recommendation, the most reliable. Ask neighbours, friends, and local estate agents who they have used recently.
- Federation of Master Builders (FMB), members must pass a vetting and inspection process before joining and follow the FMB Code of Conduct. FMB also offers free dispute resolution between its members and their clients.34
- TrustMark, the Government Endorsed Quality Scheme for work carried out in or around the home.5
- Local architect referrals, if you have an architect, ask for contractor recommendations; they will have direct experience of build quality.
Check before meeting any contractor:
- Public liability insurance (cover of £2m is a common minimum, and larger projects often ask for £5m or more)
- Employers’ liability insurance (a legal requirement for anyone with employees, with cover of at least £5 million)6
- VAT registration (a builder must register once their taxable turnover for the last 12 months goes over £90,000, so a small sole trader may not charge VAT at all)7
- Any relevant registration or certification: work on gas fittings in a home must be done by a Gas Safe registered engineer, and electricians and window installers commonly belong to schemes such as NICEIC and FENSA89
Step 3: The Site Visit
Invite each builder to carry out a site visit before they quote. A builder who quotes without visiting should ring alarm bells for anything other than very minor works. The site visit allows them to spot complications, a concrete floor that will need breaking up, a soil pipe in an awkward location, that will affect the price.
Use the visit to assess them as much as they are assessing the job. Key questions:
- Who will be on site day-to-day? (The owner, or a site manager, or subcontractors you have never met?)
- Who are their regular subcontractors for trades such as electrical and plumbing?
- Can they provide references and contact details for similar recent projects?
- What is their current programme and realistic start date?
Step 4: Reviewing the Quotes
When quotes arrive, compare them against the following framework:
| What to check | What to look for |
|---|---|
| Scope coverage | Does the quote address every item in your schedule of works? |
| Exclusions | What is explicitly excluded? (Decoration, skips, building control fees?) |
| Allowances | Are provisional sums and contingencies clearly labelled? |
| Materials | Is it clear who supplies what? Are materials specified or generic? |
| Programme | Start date, estimated duration, key milestones |
| Payment terms | Stage payments vs. monthly valuations; what triggers each payment |
| Warranties | Is any workmanship guarantee offered, and for how long? |
| VAT | Is VAT included or excluded? Check each quote is consistent |
Typical Cost Benchmarks (2026, UK excl. London)
| Project type | Typical range | Notes |
|---|---|---|
| Bathroom refit | £4,000–£12,000 | Excluding sanitaryware supply |
| Kitchen fit (excl. units) | £2,500–£6,000 | Labour only, units customer-supplied |
| Single-storey rear extension | £1,800–£3,000/m² | Including Building Regs, excl. fees |
| Loft conversion (dormer) | £45,000–£75,000 | Full turnkey inc. structural |
| Full house renovation | £600–£1,200/m² | Depending on specification |
HomeOwners Alliance gives £27,500 to £75,000 or more for a loft conversion, with an average dormer at £50,000.10 It puts a single-storey extension at £1,800–£3,000 per m² as a UK average and £2,300–£3,400 per m² in London, so expect London and the South East to sit roughly 10–30% above these figures.10 The bathroom, kitchen and whole-house rows are rough guides rather than published averages: use them to spot a quote that is far out, not to set a budget.
Step 5: The Lowest Quote Trap
The lowest quote is not always the best value. A price that is 25%+ below the other two almost always means one of:
- Items have been missed or excluded
- Cheaper materials are assumed
- The builder is buying the work and intends to recover margin through variations
- They are underpriced and may run into cash-flow problems mid-project
Equally, the highest quote is not automatically the best quality, it may simply reflect a busy contractor with a healthy order book.
The fairest approach is to select the quote that is most detailed, most complete, and from the contractor you trust most after references and the site visit. Price is a factor, but it should not be the only one.
Getting to Contract
Once you have selected a contractor, formalise the agreement. A simple written building contract protects both parties. For a homeowner dealing directly with a builder, JCT publishes the Building Contract for a Home Owner/Occupier (HO/B), which is suitable for small domestic building work such as extensions and alterations.11 It costs £40 plus VAT as a download.11 At minimum your written agreement should cover:
- Precise scope of works
- Contract sum and any provisional sums
- Payment schedule
- Start date and estimated completion
- Retention terms, if any (a small percentage held back until defects are put right)
- Defects liability period
- How variations are handled and priced
A thorough brief at the start costs you a few hours. A disputed contract at the end costs far more.
The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.
References (11)
Figures in this note were checked against the sources below on 2 October 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.
- 1technicalvery strongMinistry of Housing, Communities and Local Government.RN-QD1SFFTable 1.1 sets minimum intermittent extract rates: kitchen with a cooker hood extracting outside 30 l/s, kitchen without one 60 l/s, utility room 30 l/s, bathroom 15 l/s, sanitary accommodation 6 l/s. Extract terminals and fans other than cooker hoods should be as high as practicable and no more than 400mm below the ceiling; a cooker hood should sit between 650mm and 750mm above the hob if the manufacturer gives no figure. Table 1.7 requires background ventilators of at least 8000mm2 equivalent area in habitable rooms and kitchens for a dwelling, 10,000mm2 for a single-storey dwelling. Background ventilators should be at least 1700mm above floor level and at least 500mm from a fan in the same room. On replacement windows, paragraph 3.14 says new windows must carry background ventilators no smaller than the originals, and paragraph 3.15 gives the fallback minimums where the old size is unknown: 8000mm2 habitable rooms, 8000mm2 kitchen, 4000mm2 bathroom. Paragraph 3.32 confirms that replacing an extractor fan or cooker hood on existing cabling is not notifiable.
- 2technicalfairCitizens Advice, guidance.RN-IED4GGCitizens Advice sets out six steps for a homeowner before work starts: check if you need permission or approval, find good traders, get quotes before deciding, check that you and your trader have insurance, get a written contract, and know what to do if there are problems. Advice applies to England, with separate versions for Northern Ireland, Scotland and Wales. It names the professional registers to search: a planning consultant on the Royal Town Planning Institute website, a surveyor on the RICS website and an architect on the Architects Registration Board website. Warns that without the permission or approval needed you might be fined, prosecuted, made to put things right or undo the work, and may have problems selling later. Confirms planning permission is usually needed to build something new such as an annexe, to make a major change such as an extension, or to change the use of a building.
- 3technicalgoodFederation of Master Builders.RN-RLMBIQThe FMB is certified by the Chartered Trading Standards Institute to provide Alternative Dispute Resolution to FMB members and their clients. The scheme is free of charge, flexible and confidential, and FMB members are required to take part as a condition of the FMB Code of Conduct. It is staffed by five ADR officials, a Director, a Manager and three Case Handlers, plus a Disputes Administrator, all permanently appointed after interview and probation, given regular specialist training and covered by a conflict of interest log. The scope is limited: mediation primarily addresses workmanship issues requiring rectification by the member, and the FMB cannot mediate disputes about compensation or contractual matters, cannot give legal advice and cannot make legally binding judgments. Applications are made by online form, with a PDF or postal version available; the disputes team line is 0113 201 4263. An annual dispute resolution report is published.
- 4technicalgoodFederation of Master Builders, guidance.RN-HSH5W5The FMB's find-a-builder page. It states that members must pass a professional vetting and inspection process before joining and are bound by the FMB Code of Conduct.
- 5technicalstrongTrustMark.RN-ZGS3SNTrustMark is the government endorsed quality scheme for work in and around the home, endorsed by the Department for Energy Security and Net Zero and the Department for Business and Trade. It vets registered businesses against required standards and holds ISO 9001, ISO 27001 and Cyber Essentials accreditation. Registration is the marker to check for grant-funded energy efficiency work, so a note about a subsidised loft insulation installer should point readers here rather than to a lead generation directory.
- 6technicalvery strongGOV.UK, guidance.RN-VR45QMGOV.UK guidance for employers. It says an employer must have employers' liability insurance from the moment they employ someone, with cover of at least £5 million.
- 7technicalvery strongHM Revenue and Customs (GOV.UK), a government page.RN-J2B1F3When a business must register for VAT: the taxable turnover threshold, the backward and forward look tests, and voluntary registration. This is why a small builder's quote may carry no VAT at all while a larger firm's carries 20% on the same work, which is a genuine price difference and not a discount.
- 8technicalvery strongMinistry of Housing, Communities and Local Government.RN-SAMO3MThe official list of competent person schemes whose members can self-certify certain building work instead of getting building regulations approval, published 4 April 2013 and last updated 12 March 2018. Named schemes with contact numbers include ATTMA, APHC, Assure Certification, Blue Flame Certification, the British Board of Agrement, BESCA, Capita Gas Registration and Ancillary Services trading as Gas Safe Register, CIGA, Certass, Certsure LLP trading as NICEIC, the Elmhurst Airtightness Scheme, Fensa Limited, HETAS Limited, NAPIT Registration Limited, the National Federation of Roofing Contractors trading as CompetentRoofer, and OFTEC. Two footnotes matter: the Gas Safe Register is not technically a competent person scheme although in practice its installers carry the same building regulations responsibilities, and Benchmark Certification Limited ceased to operate as a competent person scheme on 10 February 2017, becoming part of NAPIT Registration Limited that day. Installers joining an electrical scheme are added to the single electrical competent person register.
- 9technicalvery strongHealth and Safety Executive, guidance.RN-44WXXMHSE guidance on gas safety. It states that work on gas fittings in domestic properties must be carried out by a Gas Safe registered engineer and that it is illegal for anyone else to do it.
- 10costfairHomeOwners Alliance, guidance.RN-XKP48OA price, true at 2026-09. HomeOwners Alliance's breakdown of extension costs by type, size and location, together with the fees on top: design, structural engineer, planning, building control and party wall. A consumer body rather than a cost consultancy, so the value is in listing every cost a homeowner forgets rather than in the accuracy of any one band.
- 11technicalstrongThe Joint Contracts Tribunal, guidance.RN-267X3CJCT's product page for its homeowner building contract. It says the contract is for a homeowner dealing directly with the contractor and suits small domestic work such as extensions.
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Approved Document F, Ventilation, Volume 1: Dwellings, 2021 edition, Ministry of Housing, Communities and Local Government, accessed 14 September 2026. assets.publishing.service.gov.uk
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Before you get work done on your home, Citizens Advice, accessed 30 September 2026. citizensadvice.org.uk
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Raise a dispute, Federation of Master Builders, accessed 30 September 2026. fmb.org.uk
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Find a Builder, Federation of Master Builders, accessed 30 September 2026. fmb.org.uk
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TrustMark, TrustMark, accessed 30 September 2026. trustmark.org.uk
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Employers’ liability insurance, GOV.UK, accessed 30 September 2026. gov.uk
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When to register for VAT, HM Revenue and Customs, accessed 30 September 2026. gov.uk
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Competent person scheme: current schemes and how schemes are authorised, Ministry of Housing, Communities and Local Government, accessed 2 October 2026. gov.uk
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Gas safety for employers, Health and Safety Executive, accessed 30 September 2026. hse.gov.uk
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House Extension Costs: Breakdown By Size & Type, HomeOwners Alliance, accessed 2 October 2026. Priced at 2026-09 and left there. hoa.org.uk
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Building Contract for a Home Owner/Occupier who has not appointed a consultant to oversee the work (HO/B) 2021, The Joint Contracts Tribunal, accessed 30 September 2026. jctltd.co.uk
