In 10 seconds
TrustMark is the government-endorsed scheme โ mandatory for any builder taking grant-funded work in Wales and a strong signal otherwise. FMB (Federation of Master Builders) is the largest trade body, vetting members on insurance, references, and dispute-resolution access. Verify both publicly at trustmark.org.uk and fmb.org.uk.
Why builders are different
There is no UK or Welsh statutory licence to operate as a general builder. Anyone can call themselves one. Unlike Gas Safe (gas), Part P (electrical), or FENSA (windows), there is no Competent Person Scheme that gives a builder legal self-certification for the general trade.
The legal compliance route for building work runs through Building Control โ see /regulations/building-regs-wales/ โ and the builder is one party in that process. The quality-assurance route runs through voluntary trade bodies. The two together protect a Welsh homeowner.
TrustMark โ the government-endorsed scheme
TrustMark is the only government-endorsed quality scheme for tradespeople in the UK. It's administered under licence from the Department for Energy Security and Net Zero (DESNZ) and operates UK-wide including Wales.
TrustMark membership signals:
- The contractor is vetted through site audits and customer references.
- They have valid public liability insurance.
- They use a written contract aligned with the Trading Standards Approved Code.
- Disputes can be referred to TrustMark's alternative dispute resolution provider.
- For Welsh grant-funded work (Nest, ECO4), TrustMark registration is MANDATORY โ installers without it cannot deliver Welsh Government-funded jobs.
FMB (Federation of Master Builders)
The FMB is the UK's largest trade body for the construction industry, with around 7,500 members. Membership is voluntary but vetted โ applicants must pass independent inspection of completed work and provide trade references.
FMB membership signals:
- At least one piece of work inspected by an independent surveyor on application.
- References supplied from three recent clients.
- Public liability insurance verified.
- Access to the FMB-administered Insurance Backed Guarantee scheme for warranties up to 10 years.
- A complaints procedure backed by an independent Conciliation Service.
How to verify either accreditation
Both schemes publish live searchable registers. Always check before booking โ a builder may have lapsed membership without realising or may show a card from a previous year.
- TrustMark: search at trustmark.org.uk โ filter by trade and postcode. The result shows current membership status, registered trades, and any complaint history.
- FMB: search at fmb.org.uk/find-a-builder โ same principle. Look for the company name and membership number on the result page.
NHBC and structural warranties
For new-build or major extension work, ask about NHBC (National House Building Council) cover or equivalent structural warranty (LABC Warranty, Premier Guarantee). These are 10-year insurance-backed warranties that mortgage lenders typically require for new builds. They're separate from TrustMark / FMB and apply at the project level rather than the builder level.
Red flags that signal an unverified builder
Trading Standards across Wales repeatedly identify the same patterns:
- Doorstep callers offering "we noticed your roof tiles" or "free survey because we're in the area".
- Quotes with no VAT line or no breakdown of materials vs labour.
- Cash-only or 50%+ upfront demands.
- Reluctance to provide a written contract or specify a completion date.
- Showing trade-body cards but reluctance to let you call the trade body to verify.
- No website, no Companies House registration, no fixed business address.
How to vet a Welsh builder before hiring
- Check Companies House. Search the company name at find-and-update.company-information.service.gov.uk. Active registration shows directors, accounts filed, and a UK address.
- Verify accreditations. Look them up on trustmark.org.uk and fmb.org.uk/find-a-builder. Match the membership number on their paperwork.
- See insurance certificates. Request copies of public liability (ยฃ2-5 million typical) and employers' liability (ยฃ5 million minimum if they have employees).
- Get three written quotes. For work over ยฃ1,000, never accept a single quote. Side-by-side comparison flags both pricing and scope-of-work issues.
- Insist on a written contract. Specify payment schedule (avoid 50%+ upfront), completion date, materials specification, and the dispute-resolution route.
- Confirm Building Control. For any extension, structural work, or major alteration, confirm the builder has either submitted Building Notice / Full Plans or that you will do so. See /regulations/building-regs-wales/.
Frequently asked questions
Is TrustMark the same as FMB?
No. TrustMark is the government-endorsed scheme administered under DESNZ licence; FMB is a private trade body. Both vet members but with different criteria. Many quality builders are in both โ the strongest signal is membership of both schemes plus an active Companies House record.
Do I have to use a TrustMark builder?
Only for grant-funded work (Welsh Nest, ECO4). For privately-funded work it's strongly recommended but not legally required โ you can hire any builder. The risk if uncertified: no scheme-backed warranty, no third-party dispute resolution, and harder enforcement if work fails.
What's the difference between FMB and NHBC?
FMB is a trade body โ it vets the builder. NHBC is a structural warranty provider โ it insures the building. For a new-build extension you typically want both: an FMB-vetted builder PLUS an NHBC (or equivalent) 10-year structural warranty on the work.
My builder isn't TrustMark or FMB registered. Are they automatically a risk?
No, but the burden of due diligence falls on you. Check Companies House, ask for insurance proof, get three quotes, and demand a written contract. Many excellent small builders aren't in any scheme โ but verifying them takes more effort.
Can a TrustMark builder operate anywhere in Wales?
Yes โ TrustMark operates UK-wide including all 22 Welsh local authorities. Membership doesn't restrict geography. But always check the builder's public liability insurance covers the area you're in (most do, but worth confirming for cross-border work).
What do I do if my TrustMark builder does poor work?
Step 1: raise the issue directly with the builder in writing and give them reasonable opportunity to fix. Step 2: if unresolved, raise a complaint with TrustMark via their dispute-resolution provider (currently Dispute Resolution Ombudsman). Step 3: small claims court if neither resolves the issue. Keep all written evidence.
Is TrustMark mandatory for the Welsh Nest scheme?
Yes. All Nest-funded work (boilers, insulation, heat pumps, solar) must be delivered by TrustMark-registered installers. Same for ECO4 work in Wales. If a "Nest installer" can't show TrustMark registration, walk away โ they cannot legally deliver the work.
How do I check a builder's Companies House record?
Search the company name at find-and-update.company-information.service.gov.uk. The result shows directors, registered address, accounts-filing status, and any insolvency events. Active companies with multiple years of filed accounts are lower-risk than newly-formed companies with no filing history.
Sources
- TrustMark โ find a tradesperson โ Government-endorsed quality scheme public register.
- FMB โ find a builder โ Federation of Master Builders public register.
- Companies House โ find a company โ UK Government register for company verification.
- NHBC โ structural warranty โ New-build structural warranty provider.
- Welsh Government โ Nest installer requirements โ Confirms TrustMark mandate for grant-funded work.
Find a verified builder in Wales