In 10 seconds
If your installer replaced windows after April 2002, they were legally required to either be in a Competent Person Scheme (FENSA, CERTASS, or Assure) or to obtain Building Control approval. The certificate stays with the house. Verify any FENSA certificate at forms.fensa.org.uk/fensa-certificate.
What FENSA is
FENSA stands for Fenestration Self-Assessment Scheme. It is a government-authorised Competent Person Scheme run by the Glass and Glazing Federation. Established in April 2002, it certifies that an installer's replacement window and door work meets the relevant Building Regulations.
The certificate is issued by the installer to the homeowner after work is complete. It does not expire โ it stays with the property through any future sale.
When the rules apply
Since 1 April 2002, replacing windows or external doors in a dwelling has been notifiable work under Approved Document L of the Welsh Building Regulations (conservation of fuel and power). The work must either be certified by a Competent Person Scheme member or have Building Control approval.
New-build windows and doors are covered by the construction project's overall approval โ FENSA is specifically for retrofit replacement.
Three Competent Person Schemes that count
In Wales, all three have equal legal weight:
- FENSA (Glass and Glazing Federation) โ the largest scheme, market leader since 2002, UK-wide.
- CERTASS โ not-for-profit, established 2006, equally valid legal standing, also operates in Scotland.
- Assure โ independent scheme, took over BSI's role in 2014.
Welsh Part L thermal standard for windows
For replacement windows in Wales, the whole-window U-value must not exceed 1.4 W/mยฒK (measured in accordance with Approved Document L-1B, Table 4.2). For listed buildings or properties where meeting this would alter character, secondary glazing with a centre-pane U-value of 1.2 W/mยฒK or better is acceptable.
A new Approved Document L 2026 was published with further amendments. Work commenced or notified before 1 July 2026 continues under existing rules; work after that date must comply with the 2026 edition.
What happens with no certificate
The most common consequence isn't a fine โ it's a stalled house sale. Your buyer's solicitor will require one of:
- The original FENSA / CERTASS / Assure certificate, OR
- A Building Regulations Regularisation Certificate from the local authority โ typically ยฃ250-ยฃ500, involves a site inspection and may require remedial work to bring the windows up to current Part L standards, OR
- Indemnity insurance โ typically ยฃ30-ยฃ100. Critical: indemnity must be in place BEFORE you contact Building Control about the work. Contacting the council first invalidates the cover.
How to verify a FENSA certificate
- Search the online tool. Go to forms.fensa.org.uk/fensa-certificate and enter your postcode and house number/name.
- Confirm the work. The result shows your address, the number of windows/doors registered, and the FENSA ID number. Match this against what was installed.
- Order a replacement if needed. If you've lost the paper certificate but the work IS registered, request a ยฃ25 replacement on the same page. Delivery 6-7 working days.
Frequently asked questions
Is FENSA legally required if I install my own windows?
No. DIY installation doesn't need FENSA. But the work must still meet Welsh Building Regulations Part L (thermal) and any other applicable parts. The safest route is to notify Building Control before starting โ they'll inspect and certify on completion.
What's the difference between a FENSA certificate and a product warranty?
The FENSA certificate is a Building Regulations compliance document that never expires. The product warranty (typically 10-20 years) covers manufacturing or installation defects. The certificate proves the law was followed; the warranty covers the cost of fixing things.
Can I sell my house without a FENSA certificate?
Technically yes, but the buyer's solicitor will require either the original certificate, retrospective Building Control approval, or indemnity insurance. Without one of these, completion stalls โ sometimes for weeks.
Are FENSA and CERTASS interchangeable?
For legal purposes in Wales, yes โ both are government-authorised Competent Person Schemes with identical statutory weight. The main practical difference is that CERTASS also operates in Scotland, whereas FENSA only covers England and Wales.
My windows were installed before April 2002 โ do I need FENSA?
No. The scheme only applies to windows installed on or after 1 April 2002. Pre-2002 windows are exempt โ but if you now replace them, the NEW installation must be certified.
Can I get a FENSA certificate for work that happened years ago?
Yes, IF the original installer registered the work with FENSA at the time. You can order a ยฃ25 replacement certificate. If the installer didn't register it (some don't, especially small operators), your options are Building Control regularisation or indemnity insurance โ see "What happens with no certificate" above.
Sources
- FENSA โ official site โ Scheme operator; certificate lookup and registration.
- FENSA certificate search โ Live lookup by postcode and house number.
- CERTASS โ Alternative Competent Person Scheme.
- Welsh Government โ Doors and windows building regs โ Official Welsh guidance on Part L for fenestration.
- Welsh Government โ Approved Document L 2026 โ Current 2026 thermal standards.
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