The short answer
Replacing windows is “notifiable” work under Building Regulations in England and Wales, meaning the work must meet thermal and safety standards and be registered. FENSA and CERTASS are Competent Person Schemes: a registered installer can self-certify that the work complies and register it for you, so you avoid involving the council directly. You then get a certificate — keep it, because you will need it when you sell the home. If your installer is not registered, the work must be signed off by Building Control instead. See window energy ratings explained for the standards the windows must meet.
The paperwork around replacement windows confuses many homeowners. This guide explains what Building Regulations require, what FENSA and CERTASS actually do, why the certificate matters at resale, and what to do if your windows were fitted without one.
FENSA & CERTASS at a glance
- Replacing windows Notifiable work
- FENSA / CERTASS Competent Person Schemes
- Self-certify Installer registers the work
- You receive A compliance certificate
- Needed when You sell the home
- No certificate? Building Control sign-off / indemnity
What Building Regulations require
In England and Wales, replacing windows is notifiable work because the new windows must meet minimum standards for thermal efficiency (Approved Document L), safety glass in critical locations, means of escape from certain rooms, and ventilation (Approved Document F). Someone must confirm the work meets these standards. That confirmation can come either from your local authority Building Control, or — far more commonly — from an installer registered with a Competent Person Scheme who self-certifies the work.
| Route | How it works |
|---|---|
| FENSA / CERTASS installer | Self-certifies and registers the work; you receive a certificate |
| Building Control | Council inspects and signs off if installer is not registered |
| No certificate at all | May need retrospective sign-off or indemnity insurance to sell |
What FENSA and CERTASS do
FENSA and CERTASS are the two main Competent Person Schemes for replacement windows and doors. An installer who is a member has demonstrated they work to the required standards, so they are trusted to self-certify their own installations against Building Regulations rather than calling out Building Control for every job. After the work, the scheme registers it and issues you a certificate of compliance. Using a registered installer is the simplest route and is why most homeowners choose a registered installer.
What if there is no certificate?
If windows were replaced without registration — perhaps by an unregistered fitter or a previous owner — it can be addressed at resale, usually through a retrospective Building Regulations sign-off from the council or an indemnity insurance policy that satisfies the buyer’s solicitor. It is not a disaster, but it is friction you can avoid by using a registered installer from the start. This is general guidance, not legal or regulatory advice; requirements are set by the Building Regulations in force and your local authority, so check current rules for your situation.
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Using a FENSA or CERTASS registered installer keeps the paperwork simple. Use our service to reach registered installers in your area and compare quotes.
Frequently asked questions
Do I need Building Regulations approval to replace windows?
Yes — replacing windows is notifiable work in England and Wales, and the new windows must meet standards for thermal efficiency, safety glass, escape and ventilation. The simplest way to comply is to use a FENSA or CERTASS registered installer who self-certifies the work.
What is the difference between FENSA and CERTASS?
Both are Competent Person Schemes that let registered window installers self-certify their work against Building Regulations and register it for you. They do the same job; the main difference is which scheme your installer belongs to. Either way you receive a compliance certificate.
Do I need a FENSA certificate to sell my house?
When you sell, the buyer’s solicitor will usually ask for a FENSA or CERTASS certificate for windows replaced since the rules applied. If you do not have one, it can be resolved with a retrospective sign-off or indemnity insurance, but keeping the original is far simpler.
What if my windows were fitted without a certificate?
It can be addressed at resale, usually through a retrospective Building Regulations sign-off from the council or an indemnity insurance policy. It is not a disaster, but it is avoidable friction — using a registered installer from the start prevents it.
Sources & further reading
- GOV.UK — Building Regulations and replacement windows / Competent Person Schemes
- FENSA — what FENSA is and what the certificate covers
- CERTASS — Competent Person Scheme registration and certificates
- GOV.UK / Building Regulations Approved Documents L and F — thermal and ventilation standards
This is general information, not legal, regulatory or advice for your specific property. Requirements are set by the Building Regulations in force and your local authority. Replacement windows should be fitted by a FENSA or CERTASS registered window installer. We are an independent information and introduction service, not an installer.