Compare Builders: How to Check They Are FENSA Registered in 2026
FENSA registration only covers replacement windows and doors in England and Wales, so before you hire, check the installer's FENSA number on the official register at fensa.org.uk, ask to see a recent FENSA certificate from a past job, and confirm whether your specific work is covered by FENSA, a rival scheme like CERTASS, or a building control notice instead. This guide shows you exactly how to verify a firm in five minutes and how the three compliance routes compare.
How to check a builder is FENSA registered — at a glance
Verify any window or door installer in five steps:
- Ask for their FENSA registration number — a genuine installer will give it without hesitation.
- Check it on the official register at fensa.org.uk using the “Find an Installer” and certificate-check tools.
- Ask to see a recent FENSA certificate from a completed job to confirm they actually self-certify their work.
- Confirm the scheme fits your job — FENSA only covers replacement windows and external doors, not extensions or structural work.
- Cross-check reviews and insurance — public liability of at least £2m and independent reviews.
If the work isn't replacement glazing, FENSA won't apply — the installer will instead use a rival competent-person scheme such as CERTASS, or notify the work to building control. All three routes are legitimate; what matters is that one of them is in place so your windows are certified as Building-Regulations compliant.
From the editorial desk
The single most common misunderstanding we see is homeowners asking a general builder or extension firm whether they are “FENSA registered.” FENSA is a competent-person scheme specifically for replacement windows and doors — a builder pouring foundations or building an extension has no reason to be on it, and its absence tells you nothing about their competence for that work. Match the credential to the job.
When the job is replacement glazing, the FENSA certificate matters for a very practical reason: it's the document a buyer's solicitor asks for when you sell. No certificate (and no building-control completion certificate as the alternative) can stall a sale or force you to buy indemnity insurance. So checking registration up front isn't box-ticking — it protects the resale value of your home. Verify the number on the register yourself; don't take a logo on a van or website at face value.
How to verify a FENSA installer in five minutes
Work through these in order before you sign anything. Each one takes a minute or two and together they weed out the vast majority of rogue or lapsed installers.
1. Get the FENSA registration number
Ask directly: “What's your FENSA registration number?” A legitimate installer answers immediately. Vagueness, deflection or “we're covered, don't worry” is a red flag — every registered firm has a unique number.
2. Check the official FENSA register
Go to fensa.org.uk and use the “Find an Installer” search. Confirm the company name and area match what you've been told. The register is the single source of truth — a website badge is not.
3. Ask to see a recent FENSA certificate
A registered installer issues a FENSA certificate for every notifiable job, usually within a few weeks of completion. Ask to see a redacted recent one — it proves they actually self-certify rather than just holding lapsed membership.
4. Confirm the scheme suits your work
FENSA only covers replacement windows and external doors in existing dwellings. New windows in an extension are certified through building control as part of the extension, not FENSA. If a firm insists FENSA covers structural or extension work, they've misunderstood the scheme.
5. Cross-check insurance and reviews
Ask for proof of public liability insurance (at least £2m) and any insurance-backed guarantee on the installation. Then check independent reviews. Registration plus insurance plus a solid review history is the combination you want.
FENSA vs CERTASS vs building control (2026)
The three legitimate ways replacement glazing is certified as Building-Regulations compliant in England and Wales. Any one is fine — you just need to know which route your installer is using and get the paperwork.
Both FENSA and CERTASS are government-authorised competent-person schemes, so a member installer can self-certify without a separate building-control application. If your installer is on neither, the work must be notified to building control before it starts — make sure that's happening, or you'll be missing the certificate a future buyer needs.
Warning signs to walk away from
Any one of these on its own is a reason to pause; two or more and we'd suggest getting other quotes.
❌ Won't give a registration number
A firm that dodges the question, or claims their number “isn't needed,” either isn't registered or is hoping you won't check. Every FENSA or CERTASS member has a verifiable number.
❌ Logo on the van but not on the register
Badges are easy to print and memberships lapse. If the company name doesn't appear on the official online register, treat the badge as decoration, not proof.
❌ “We'll sort the certificate later” — for cash
Pressure for cash payment with a promise to handle compliance afterwards often means no certificate ever appears. Get the compliance route confirmed in writing before work starts.
❌ Claims FENSA covers an extension
FENSA is glazing-only. A firm that says it covers your extension or structural work has misunderstood the scheme — that work belongs to building control.
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Frequently asked questions
Six questions UK homeowners ask us most often about checking a FENSA installer in 2026.
Ask the installer for their FENSA registration number, then check it on the official register at fensa.org.uk using the “Find an Installer” search. Confirm the company name and area match, and ask to see a recent FENSA certificate from a completed job. Never rely on a logo on a van or website — only the official register confirms current membership.
FENSA is a government-authorised competent-person scheme for the installation of replacement windows and external doors in existing dwellings in England and Wales. It lets a registered installer self-certify that the work meets Building Regulations (mainly thermal performance and safety) and issue a FENSA certificate, without a separate building-control application. It does not cover extensions, conservatories with structural work, or new-build glazing.
Yes. CERTASS is another government-authorised competent-person scheme for windows and doors, functionally equivalent to FENSA. A CERTASS-registered installer can self-certify and issue a CERTASS certificate that a solicitor will accept in exactly the same way. What matters is that your installer is registered with one recognised scheme — not which one.
Then the work must be notified to your local authority building control before it starts, and inspected to issue a completion certificate. This is legitimate but slower and usually costs a council fee. The risk is a firm that is on no scheme and hasn't notified building control — you'd end up with no compliance certificate at all, which causes problems when you sell.
When you sell, the buyer's solicitor asks for proof that replacement windows and doors fitted since April 2002 are Building-Regulations compliant. A FENSA (or CERTASS, or building-control) certificate is that proof. Without it you may have to buy indemnity insurance or the sale can be delayed, so keeping the certificate safe protects your home's resale value.
Not for general building work. FENSA is specific to replacement windows and doors, so a builder doing an extension, structural work or groundworks has no reason to be on it. For those trades, look instead for relevant memberships such as the FMB, appropriate insurance, structural warranties and building-control involvement. Match the credential to the job.
Sources used in this guide
- FENSA — Official installer register and certificate-checking tools
- CERTASS — Rival competent-person scheme register
- gov.uk — Building Regulations Approval — Competent-person schemes and the building-control route
- FMB — Federation of Master Builders — Vetting general builders on wider projects
Methodology note: Scheme details reflect published 2026 guidance from FENSA, CERTASS and gov.uk. Last fact-checked: . Spotted something that looks wrong? Email editorial@bestbuilders.co.uk.
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