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; 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.
I have seen plenty of jobs where scheme registration was 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.
Tom Bradley, window installer
What the certificate actually certifies
Most people assume a FENSA certificate is only about energy efficiency. It is broader than that. The building regulations that apply to a replacement window cover thermal performance, safety glazing, ventilation, means of escape and, on some front doors, level access. The certificate is a declaration that the whole set has been met. That is worth knowing, because it explains why a cowboy job can fail on things that have nothing to do with the glass spec.
- Thermal performance. A replacement window must achieve a whole-window U-value of 1.4 W/m²K or better, or carry a Window Energy Rating of band B or better. Our Part L guide sets out both routes and which one your quote is likely to use.
- Safety glazing. Toughened or laminated glass is required in critical areas: any panel up to 800mm from floor level, any glazed door up to 1500mm from floor level, and any side panel within 300mm of a door edge up to 1500mm from the floor.
- Means of escape. A replacement window must give at least the same escape potential as the one it replaces. Where an egress window is required, the clear openable area must be no less than 0.33m², with neither width nor height below 450mm, and the bottom of the opening no more than 1100mm above the floor.
- Ventilation. Background ventilation has to be maintained, which in practice is what trickle vents are for. This is the requirement most often missed on cheap replacement jobs.
- Access. On dwellings built since 1999, replacing the main entrance door must not make the threshold worse than it was.
The technical detail sits in the Approved Documents, and the Planning Portal summarises what applies to doors and windows in plain terms. Worth a read before you accept a quote that seems suspiciously cheap.
What FENSA covers and what it does not
FENSA covers the replacementof 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. 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.
Why the certificate matters when you sell
The certificate is your evidence of compliance, and it becomes important at two moments. First, it confirms the windows actually meet the Part L energy standardsyou paid for, which is the thing you are buying. Second, and far more practically, the buyer's conveyancer will ask for it. Replacement windows appear on the standard property information form, the local authority search will show any building control record, and mortgage lenders frequently insist the certificate file is complete before they release funds.
Certificates are transferable. They attach to the property, not to you, so the one issued to a previous owner is the one your buyer wants to see. Keep it with the deeds along with the installer's workmanship guarantee, which is a separate document covering faults rather than compliance. If you have recently had work done and the certificate has not arrived, allow a few weeks: the installer notifies FENSA, FENSA notifies your local building control, and the certificate typically reaches you around two to four weeks after completion.
What happens to a house sale when there is no FENSA certificate
This is the situation that brings most people to this page, and it is worth being blunt about it. If windows were fitted after 1 April 2002 with no competent person scheme certificate and no council Building Regulations approval, the work is unauthorised. Ignoring the building regulations is a criminal offence, though in practice enforcement against a homeowner who inherited the problem is rare. What is not rare is the sale stalling while solicitors argue about who pays to sort it.
You have four realistic options, in descending order of how well they work.
- Find the certificate.Check the FENSA address lookup, then the other five schemes, then your conveyancer's local authority search. A surprising number of missing certificates were never missing, just filed somewhere else.
- Apply for regularisation. Your local authority building control team can issue a regularisation certificate for unauthorised work started on or after 11 November 1985. This is the only route that actually makes the work authorised.
- Buy a building regulations indemnity policy.This does not fix anything. It compensates the owner if the council enforces. Buyers' solicitors accept it routinely, which is why it is so common.
- Negotiate. Reduce the price by the cost of putting it right and let the buyer deal with it. Sometimes the cleanest answer, especially if the windows are old enough that the buyer wants to replace them anyway.
| Scenario | What it means for you |
|---|---|
| FENSA certificate held | Compliant, easy sale, no further action |
| Different scheme (e.g. CERTASS, NAPIT, ASSURE) | Equally valid; check that scheme's records for the equivalent certificate |
| Certificate lost but job was registered | Order a replacement copy from FENSA for £30 including VAT |
| No certificate, post-2002 work | Regularisation certificate or a building regulations indemnity policy |
| Windows fitted before 1 April 2002 | No certificate was ever required; say so and move on |
| Conservatory, porch or extension glazing | Outside the FENSA scheme; different building control evidence applies |
General guidance, not legal advice. Confirm with your conveyancer when buying or selling.
How to regularise windows retrospectively, and what it costs
You cannot get a FENSA certificate retrospectively for a job that a non-registered installer did. The scheme only certifies work carried out by its own approved installers who notified it at the time. The retrospective route is a regularisation certificate from your local authority, applied for under regulation 18 of the Building Regulations 2010. The council inspects what is there, tells you what needs changing, and issues the certificate once the work complies. Depending on what they find, that can mean opening up reveals or replacing glass that fails the safety or thermal requirements.
Fees are set locally and are VAT exempt for regularisation, so they vary. Two published 2026 schedules give a useful sense of the range. Oxford City Council charges £500 to regularise new and replacement windows and doors of up to seven windows and two doors, against £400 for the same work approved in advance, because its regularisation charge is the standard fee plus 50%. Coventry City Council charges £277.50 plus £30 per window for regularisation of replacement windows fitted by an unregistered installer, which works out at £517.50 for a typical eight-window house, against £185 plus £20 per window if you had applied before the work started.
| Route | Typical cost | Does it make the work compliant? |
|---|---|---|
| FENSA certificate via a registered installer | Included in the installation price | Yes, and no council fee to pay |
| Replacement copy of a lost FENSA certificate | £30 including VAT | Yes, if the job was registered originally |
| Building control approval before work starts | £400 (Oxford) or £185 plus £20 per window (Coventry) | Yes |
| Regularisation certificate after the event | £500 (Oxford) or £277.50 plus £30 per window (Coventry) | Yes, once any remedial work is done |
| Building regulations indemnity policy | From around £20 including IPT | No, it only insures against enforcement loss |
Sources: FENSA certificate ordering page; Oxford City Council and Coventry City Council building control fee schedules, both effective 1 April 2026; GCS Title building regulations indemnity policy summary. Council fees are set locally and vary; check your own authority.
Figures above come from the Oxford City Council and Coventry City Council published fee schedules, and the Planning Portal regularisation guidance explains the process. Your own council will publish its own numbers, and they differ enough that it is worth looking yours up rather than assuming.
The cheapest mistake to avoid is the dearest one to fix later. Spend nothing now by checking the installer registers the job, or spend several hundred pounds later on regularisation when you try to sell. Easy choice.
Tom Bradley, window installer
What a building regulations indemnity policy costs, and when it is accepted
A building regulations indemnity policy, often sold under the name FENSA indemnity or lack of building regulations approval cover, is the shortcut most conveyancers reach for. It is a one-off premium, it issues in minutes, and it runs in perpetuity and passes to future owners. Premiums start from around £20 including insurance premium tax for a standard residential policy, and conveyancers commonly quote a broader range of £180 to £500 where the indemnity limit is high or the breach covers more than windows. It is normally the seller who pays, as a goodwill gesture to keep the sale moving.
Understand precisely what you are buying, because it is narrower than people think.
- It does not make the work compliant. The windows remain unauthorised. The policy only pays out if the local authority takes enforcement action and you suffer a loss as a result.
- It does not pay to replace the windows. It will not fund a compliant installation, and it does not cover personal injury caused by faulty workmanship.
- There is a qualifying period. Insurers set their own. One widely used residential policy requires the window installation to have been completed at least three months before cover starts, while conveyancers often work to a rule of thumb that the work should be more than a year old.
- Approaching the council voids it. Once you have contacted building control about the specific work, you can no longer insure it. Decide which route you are taking before you pick up the phone. This is the single most common way people lock themselves out of the cheap option.
- It reappears at the next sale.The policy transfers, but so does the underlying non-compliance. Your buyer's buyer will ask the same question in five years.
Terms and premiums here follow the published GCS Title building regulations policy summary and the conveyancing guidance published by SAM Conveyancing. Policies differ, so read the one you are actually offered.
Can the council still act? The 10-year enforcement window
A lot of advice online still says the council only has 12 months to act, so older windows are safe. That is out of date and it matters. The Building Safety Act 2022 extended the enforcement period under section 36 of the Building Act 1984 from 12 months to 10 years from completion of the work. A section 36 notice requires the owner to pull down, remove or alter non-compliant work, and if it is ignored for 28 days the authority can carry out the work itself and recover the cost from the owner.
Two related time limits are worth keeping straight. A compliance notice, which requires a contravention to be remedied, must be issued within 12 months of the contravention. Prosecution under section 35 of the Building Act 1984 carries no time limit at all and can result in an unlimited fine, but that action is normally taken against the person who carried out the work rather than the homeowner. The Planning Portal enforcement guidance sets out all three.
The practical upshot for a seller is simple: windows fitted within the last 10 years carry real enforcement exposure, and a buyer's solicitor is right to press on them. Windows fitted 15 years ago carry effectively none, and an indemnity policy on those is cheap peace of mind rather than genuine risk transfer.
How to check your windows are registered
Use the certificate lookup on the official FENSA website: enter your address and it lists any registered installations at the property. A replacement copy costs £30 including VAT. If nothing shows up, do not assume the worst. FENSA itself lists several innocent explanations: the postcode is wrong, the job included more than replacing windows and doors, the glazing is internal, the company was not FENSA approved at the time (in which case check the other five schemes), or the installer simply never notified the scheme when the job completed.
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, where notifiable work needs a building warrant from the local authority and a completion certificate at the end. Northern Ireland runs its own building control regime through district councils. 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.
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.
It is your proof that the windows comply with Building Regulations, including the Part L energy requirements. You will usually need it when you sell the house, because the buyer's solicitor asks for it and mortgage lenders often want the paperwork complete. Missing certificates can delay or jeopardise a sale.
If replacement windows were fitted after 1 April 2002 without a FENSA (or equivalent) certificate or council Building Regulations approval, the work is unauthorised. You have three practical routes: apply to the council for a regularisation certificate, buy a building regulations indemnity policy to satisfy the buyer's solicitor, or negotiate a price reduction. Only regularisation actually fixes the problem.
Not if the installer was not FENSA-registered at the time. FENSA certificates can only be issued by a FENSA Approved Installer who notified the scheme when the job finished. If the work was never registered, the retrospective route is a regularisation certificate from your local authority building control team, not a FENSA certificate. If the job was registered and you have simply lost the paperwork, you can order a replacement copy from FENSA for £30 including VAT.
Premiums start from around £20 including insurance premium tax for a standard residential policy, and conveyancers commonly quote a range of roughly £180 to £500 where the sum insured is high or the breach is broader than windows alone. The policy runs in perpetuity and passes to future owners, but it only compensates for enforcement losses. It does not make the windows compliant and it does not pay to replace them.
A section 36 notice, which requires unauthorised work to be removed or altered, can be issued up to 10 years after the work was completed. The Building Safety Act 2022 extended this from the previous 12 months. Prosecution under section 35 of the Building Act 1984 has no time limit at all, though that action is usually taken against the installer rather than the homeowner.
Use the certificate lookup on the official FENSA website. You enter your address and it shows any registered installations. If nothing appears, the installer may have used a different competent person scheme such as CERTASS, Certsure, NAPIT, ASSURE or Blue Flame, or the job may never have been notified at all. Your conveyancer's local authority search will also show any building control record.
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, or commercial properties. Secondary glazing added inside an existing window is not a replacement either, so it sits outside the scheme.
No. FENSA certifies that the work meets Building Regulations. A workmanship or product guarantee is separate, and FENSA Approved Installers must supply an insurance-backed guarantee that stands if the firm stops trading. You should have both: the certificate for compliance and a written insurance-backed guarantee for faults.
No. FENSA is authorised for England and Wales only. Scotland runs a separate building warrant and completion certificate system under Scottish 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.