FENSA is the Fenestration Self-Assessment Scheme. When a FENSA-registered installer fits your replacement windows, they self-certify that the work meets Building Regulations, notify your local council on your behalf, and you receive a FENSA certificateas proof. That certificate matters most when you come to sell, because the buyer's solicitor will ask for it and a missing one turns a routine enquiry into a negotiation. Checking an installer is registered before you sign is one of the simplest ways to protect yourself from a poor deal, and it costs you nothing.
What FENSA actually does
Since 1 April 2002, building regulations have applied to all replacement glazing in England and Wales. An external window or door counts as a controlled fitting, which means replacing one is notifiable building work in the same way a new boiler or a rewire is. The same applies to roof lights. The one exception is a replacement external door whose door and frame together are 50% glazed or less: Schedule 4 of the Building Regulations 2010 exempts it from notification, though it must still comply. If you are fitting one yourself, both cases are set out in how to fit a uPVC door. What you get at the end is a compliance certificate proving building regulation compliance for window and door installations, issued either by the scheme or, if your fitter is not a member, by your local council once the work is registered with them; controlled fitting, competent person scheme and self-certification are the terms this page turns on, and our double glazing glossary defines each in a line, so start with the Double Glazing Glossaryif the wording is unfamiliar. Normally that would mean involving your local council's Building Control, paying their fee and booking their inspection. FENSA exists so a registered installer can self-certify the work instead, which is faster and cheaper for you. The certificate they issue is the document that says the job complies.
FENSA is the largest of the schemes but it is not the only one. The Ministry of Housing, Communities and Local Government authorises six competent person schemes for replacement windows, doors, roof windows and rooflights in existing dwellings: Blue Flame Certification, CERTASS, Certsure (which trades as NICEIC), FENSA, NAPIT and ASSURE. A certificate from any of them is equally valid, which is why a property with no FENSA record is not automatically a property with a problem. Check the other schemes before you panic. FENSA covers replacement windows; secondary glazing added inside an existing window is not a replacement, so it sits outside the scheme entirely.
| Scheme | Short name | Covers replacement windows and doors |
|---|---|---|
| Fensa Limited | FENSA | Yes, existing dwellings and other existing buildings |
| Certass Limited | CERTASS | Yes |
| Certsure LLP (NICEIC) | Certsure | Yes |
| NAPIT Registration Limited | NAPIT | Yes |
| Assure Certification Limited | ASSURE | Yes |
| Blue Flame Certification Limited | Blue Flame | Yes |
Source: MHCLG list of current competent person schemes on GOV.UK, checked 29 July 2026. A certificate from any of these six satisfies Building Regulations.
Scheme registration is regularly the difference between a smooth sale and a stalled one. If a fitter cannot tell you which scheme they belong to, that is your cue to stop the conversation. Self-certification is not optional, it is the law.
Double Glazing Cost Calculator Team
Certass or FENSA: is there a difference?
Not one that affects you. Both are authorised competent person schemes on the same MHCLG list, so a CERTASS certificate and a FENSA certificate satisfy Building Regulations equally and a conveyancer should accept either. The difference is commercial rather than legal: FENSA is the larger scheme, so more homes have a FENSA record, and an installer joins whichever one suits their trade body and their paperwork.
The practical consequence is the one worth remembering. If you search the FENSA register and find nothing, that is not evidence the work was never notified. It is evidence the work was not notified through FENSA. Check CERTASS and the other four schemes before you assume there is a problem, because an unnecessary indemnity policy is a cost you can talk yourself into.
Is Assure Certification the same as FENSA?
No, ASSURE is a separate company, and yes, its certificate does the same job. Assure Certification Limited appears on the same list of six authorised schemes in the table above, so windows registered with ASSURE are certified to the identical standard and need no FENSA record alongside them.
This one catches sellers out more than the others, because ASSURE is newer and less recognised than FENSA, and a buyer's solicitor who has not seen one before may query it. The answer is the MHCLG list itself: the scheme is government-authorised, and the certificate is proof of compliance in its own right rather than a substitute for one.
What FENSA covers and what it does not
FENSA covers the replacement of external windows, doors, roof windows and rooflights in a home that stays on its original footprint, with the use and size of rooms unchanged. It does not cover conservatories, porches, new builds, extensions, repairs where the frame is not replaced, or commercial properties. Glass-only work, such as a new sealed unit or an encapsulated stained glass panel fitted into the existing frame, is a repair and sits outside it. FENSA's compliance guide (v2023.07) also puts listed buildings outside the scheme, so replacement windows on a listed home are signed off by local authority building control rather than FENSA; conservation areas are in scope, though FENSA may ask to see the planning approval. This trips up a lot of sellers. If your buyer's solicitor asks for a FENSA certificate for a conservatory, the correct answer is that FENSA never covered it, and a different form of building control evidence applies. Equally, if your windows sit in a conservation area or listed building, planning consent is a separate question from building regulations and a FENSA certificate says nothing about it.
Your FENSA certificate
When a registered installer finishes the job, they register it with FENSA, which asks for that within 21 days of completion, and FENSA then posts the certificate, usually within 15 days of registration. The certificate declares that the replacement meets the building regulations that apply to it: thermal performance under Part L, safety glazing, background ventilation through trickle vents, and escape where the room needs one of the fire escape windowsthe regulations describe. It attaches to the property rather than to you, and a buyer's solicitor will ask for it when you sell.
A lost certificate can be reordered from FENSA for £30 including VAT. Where there is no certificate at all, because the fitter was not in a scheme or never registered the job, the fixes are council regularisation or an indemnity policy, and neither is as cheap as getting it right at the start. That is the cost that rarely gets counted when people weigh up fitting their own windows. Our guide to how to get a FENSA certificate covers delivery, replacement copies, unregistered jobs, selling without one and the council's enforcement time limits.
Before you buy windows, confirm the installer's scheme membership in writing, get the registration number, and make sure the certificate is explicitly part of what you are paying for. Do that across all three of your comparison quotes and you will quickly see which firms are serious. Once you have lined up a registered fitter, price the job in the uPVC window calculator so you know a fair figure before the quotes arrive.
Scotland and Northern Ireland
FENSA is authorised for England and Wales only. Scotland operates a separate system under Scottish building standards. A replacement window where the frame is replaced needs no building warrant under Schedule 3 of the Building (Scotland) Regulations 2004, though it must still meet the standards; cutting down, building up or widening the opening does need one. Northern Ireland runs its own building control regime through local councils, and Building Control NI says no application is needed to install replacement windows, though the work must still meet the relevant requirements of the Regulations. If your property sits outside England and Wales, ask your conveyancer which local evidence a buyer will expect, and do not accept a seller's assurance that FENSA covered it, because it cannot have.
Get quotes from registered installers
Whoever fits your windows has to self-certify the work against building regulations, or you need building control to sign it off separately. Tell us what you need and Leads 2 Trade will arrange quotes from installers covering your postcode.
Ask for the scheme and the registration number at quote stage, not after the job. FENSA and CERTASS are both valid, whatever a salesperson implies about the other one, and the certificate is the thing your buyer's solicitor will ask for.
Frequently asked questions
FENSA is the Fenestration Self-Assessment Scheme. It is a government-authorised competent person scheme covering England and Wales. A FENSA certificate proves your replacement windows and doors meet Building Regulations without needing separate sign-off from your local council, because the registered installer self-certifies the work and notifies the council on your behalf.
Your installer registers the job with FENSA, which asks for that within 21 days of completion, and FENSA posts the certificate, usually within 15 days of registration. A lost copy costs £30 including VAT from FENSA. Our FENSA certificate guide covers replacement copies, jobs that were never registered, and selling a house without a certificate.
FENSA covers replacement of external windows, doors, roof windows and rooflights in an existing home on its original footprint. It does not cover conservatories, porches, new builds, extensions, repairs where the frame is not replaced, listed buildings, or commercial properties; work on a listed building goes to local authority building control instead. Secondary glazing added inside an existing window is not a replacement either, so it sits outside the scheme.
No. FENSA is authorised for England and Wales only. In Scotland a replacement window where the frame is replaced needs no building warrant under Schedule 3 of the Building (Scotland) Regulations 2004, though it must still meet the building standards, and Northern Ireland has its own building control arrangements. If your property is outside England and Wales, ask your conveyancer which local evidence of compliance a buyer will expect.
Not all, but reputable ones belong to FENSA or an equivalent competent person scheme. For replacement windows and doors in an existing dwelling, the authorised schemes are Blue Flame Certification, CERTASS, Certsure, FENSA, NAPIT and ASSURE. Always confirm membership in writing before you sign, because an unregistered fitter cannot self-certify, leaving you to arrange council approval yourself.