FENSA Certificate Explained for UK Homeowners in 2026

FENSA is the paperwork you rarely think about until it matters. When you replace a window or a door in England or Wales, the installation has to meet Building Regulations. A FENSA certificate is the document that proves it does, and without one at the right moment, a property sale can stall or a remortgage can drag out for weeks.

The certificate itself is straightforward once you know what it is. But the scheme sits in a fog of similar-sounding language (“FENSA-approved”, “FENSA-accredited”, “our subcontractors are FENSA-registered”) that makes it hard for homeowners to know what they should actually be looking for when hiring an installer.

This guide covers what FENSA is, what the certificate proves, when you need one, and how to check that the installer you are about to hire is genuinely registered. It’s the piece of paperwork that follows your windows for the life of the property, so it’s worth understanding.

What FENSA actually is

Before we get to what a certificate covers, it helps to understand what FENSA is and why it exists at all.

The organisation

FENSA (Fenestration Self-Assessment scheme) is a government-authorised competent persons scheme run by the Glass and Glazing Federation. It was set up in April 2002 in response to changes to Building Regulations that required all replacement windows and doors in England and Wales to meet minimum thermal performance standards.

The competent persons scheme

Before FENSA existed, every replacement window installation technically required Building Control notice and inspection from the local council. That was slow, expensive and unworkable at scale. The competent persons scheme allows registered installers to self-certify their own work as compliant with Building Regulations, which saves homeowners the cost of a separate Building Control application.

Who runs it and where it applies

FENSA is one of several competent persons schemes in England and Wales. Others include CERTASS and BM TRADA. All three do the same job legally, but FENSA is by some distance the most established and most widely recognised, particularly for residential installations. Scotland has its own equivalent through Trading Standards, and Northern Ireland has separate arrangements. This guide focuses on England and Wales where FENSA applies.

What a FENSA certificate actually is

The certificate is the document that homeowners actually see and need to keep hold of. Here’s what it contains and how you get it.

What is on the certificate

A FENSA certificate is a document issued after a replacement window or door installation is completed by a FENSA-registered installer. It confirms four things: that the installer was FENSA-registered at the time of installation, that the installation meets the relevant Building Regulations for thermal performance, safety glazing, escape windows and ventilation, that the installer has notified FENSA (who then notifies the local authority), and the property address and installation date.

When you receive it

FENSA certificates are issued within 30 days of the installation being completed. It arrives directly from FENSA (not the installer) and is registered against the property address. The certificate stays with the property for the life of the installation, so when you sell, it transfers to the new owner as part of the property paperwork.

Certificate vs notification

You will see two related terms: the FENSA notification (which is the installer telling FENSA the work is done) and the FENSA certificate (which is the document FENSA sends you afterwards). Both refer to the same thing legally, but “certificate” is what conveyancers and mortgage lenders ask for at sale time.

When you actually need a FENSA certificate

FENSA certificates matter at very specific moments, and most of them are moments you can’t control the timing of.

When you sell your home

Buyers’ solicitors ask for a FENSA certificate for every window and door installation completed in the past 10 years. Without one, the sale can be delayed until you either produce the certificate or buy retrospective indemnity insurance. Indemnity insurance typically costs £150 to £400 and covers only the risk of Building Control enforcement, not the quality of the work itself.

When you remortgage or take equity release

Mortgage lenders often request FENSA certificates as part of the property survey process. Missing certificates are one of the more common reasons a remortgage application gets delayed.

When you make an insurance claim

If a storm damages a window and you claim on your home insurance, the insurer will typically ask when the window was installed and by whom. A FENSA certificate confirms both, and can speed up the claim.

When you claim on the installation guarantee

Most window installation guarantees, including Cristal Windows’ 10-year insurance-backed guarantee, require the original FENSA certificate as evidence that the installation was completed by a registered installer. If a guarantee claim comes up 8 years after installation, the certificate is what proves the installer was FENSA-registered at the relevant time.

When you don’t need FENSA

FENSA is only required for replacement windows and doors. It’s not required for new-build installations (which are covered under the initial Building Regs sign-off), not for internal doors (which aren’t governed by the same Building Regs), and not required for standard conservatories. That said, tiled conservatory roofs and other structural changes may still require FENSA certification for the glazed elements.

What Building Regulations FENSA actually covers

FENSA certifies compliance with specific parts of the Building Regulations. Understanding what’s covered helps homeowners know what they’re getting.

Thermal performance (Approved Document L)

The main regulation FENSA certifies is Part L of the Building Regulations, which sets minimum U-values for replacement windows and doors. Replacement windows must achieve a U-value of 1.4 W/m²K or better. Modern uPVC and aluminium products from mainstream systems houses (Rehau, AluK, Smart) exceed this comfortably.

Safety glazing (Approved Documents N and K)

Glass installed in critical locations, low-level windows, doors, sidelights and areas near stairs, must be toughened or laminated safety glass. FENSA registration confirms the installer has selected the correct glass for each location on the job.

Escape windows (Approved Document B)

First-floor bedrooms and upper habitable rooms typically require at least one window that meets minimum escape dimensions in case of fire. FENSA certifies that any bedroom windows replaced still meet these dimensions.

Ventilation (Approved Document F)

Rooms need adequate background ventilation to prevent condensation and damp. Trickle vents (or equivalent controlled ventilation) are required in most replacement installations. FENSA registration confirms this is in place.

What FENSA doesn’t cover

FENSA doesn’t cover installation quality beyond Building Regs compliance, doesn’t cover the products themselves (that’s the manufacturer’s guarantee), and doesn’t cover structural work like new openings or moved windows. Structural changes still require a separate Building Control application even when the windows themselves are FENSA-certified.

How to check an installer is actually FENSA-registered

This is the section that matters most for anyone about to hire an installer. Five quick checks can save you from the wrong choice.

Ask for the registration number

Every FENSA-registered installer has a unique registration number. A genuine installer will give this to you without hesitation. It’s usually printed on quotes, letterheads and the company website. Cristal Windows’ FENSA registration number is [NUMBER TO CONFIRM].

Check the FENSA installer directory

Go to the FENSA installer directory and search by company name or registration number. If the installer is genuinely registered, they’ll appear immediately with their trading address and the categories of work they’re approved for.

Watch for the common misdirection

Some installers say “we work with FENSA-registered subcontractors” or “our work is FENSA-approved” without being registered themselves. These claims are not the same as being registered. Only the FENSA-registered company that carried out the installation can issue a certificate for it.

Check the categories they cover

FENSA registration covers different categories: replacement windows, doors, roof lights, and conservatories. An installer registered for windows only cannot issue a FENSA certificate for a door installation. Ask what categories they’re registered for and check this against the work you’re getting done.

Ask when the certificate will arrive

A genuine FENSA-registered installer will explain the certificate arrives directly from FENSA within 30 days. If an installer says they’ll issue the certificate themselves, or hands you a “certificate” on the day of installation, something is wrong. FENSA certificates only come from FENSA.

Warning signs when hiring an installer

Beyond FENSA specifically, a few common warning signs suggest an installer isn’t quite what they seem.

They can’t produce a registration number

Any legitimate FENSA installer knows their registration number or has it printed on their paperwork. Hesitation or evasion is a red flag.

They quote significantly below market rate

If a quote comes in 30 to 40 percent below other installers, the saving usually comes from cutting corners: uncertified glass, no Building Regs paperwork, cash-in-hand arrangements. There is no legitimate way to install compliant windows at that discount level.

They pressure a same-day decision

Genuine installers give you time to compare quotes, check credentials and read the small print. Pressure to sign that day usually means they don’t want you checking.

They ask for large upfront payments

Standard practice for a full window replacement is a small deposit (typically 10 to 20 percent) with the balance due on completion. Requests for 50 percent or more upfront are unusual and worth questioning.

The paperwork doesn’t match

If the quote is from one company name and the invoice or FENSA certificate names a different entity, ask why. Legitimate installers work under one trading name that appears consistently across all their paperwork.

What to do if you don’t have a FENSA certificate

A missing certificate isn’t necessarily a disaster. Here are the options, in order of preference.

Check if one was ever issued

Contact FENSA directly through their website. Their records go back to 2002. If a certificate was ever issued for your property, they can send you a replacement, usually for a small administration fee.

Contact the original installer

If the installer is still trading, they can look up the notification they submitted and confirm the certificate reference. Most will do this free of charge.

Retrospective indemnity insurance

If no certificate exists, buyers’ solicitors will typically accept a retrospective indemnity insurance policy at property sale. These cost £150 to £400 through most conveyancers and cover the risk of Building Control enforcement.

Late notification

For work done in the past 12 months, some installers may still be able to submit a late notification to FENSA. This is at FENSA’s discretion and usually incurs a fee. It’s not an option for older installations.

Retrospective Building Control approval

If the work is more than 12 months old, no certificate exists, and no insurance route is acceptable, you can apply retrospectively for Building Control approval through the local council. This typically involves a full inspection, potential remedial work, and a fee of several hundred pounds. It’s a last resort but is legally clean.

How Cristal Windows handles FENSA

Cristal Windows has been FENSA-registered since [YEAR TO CONFIRM]. Our registration number is [NUMBER TO CONFIRM] and you can verify it on the FENSA installer directory at fensa.org.uk.

Every eligible window and door installation we complete is notified to FENSA within 30 days. FENSA then issues the certificate directly to the property address, so it stays on record for the life of the installation. There’s no additional cost to you and no paperwork you need to complete.

Alongside FENSA registration we carry the following credentials:

• Which? Trusted Trader
• Glass and Glazing Federation member (34+ years)
• Rehau Authorised Partner for uPVC systems, alongside AluK and Smart for aluminium
• Insurance-backed 10-year installation guarantee

The FENSA certificate is one piece of the paperwork stack a homeowner should expect. It’s the most legally significant piece, but it works alongside our installation guarantee, product manufacturer warranties, and standard Consumer Protection legislation.

FENSA-registered vs FENSA-approved: what’s the difference?

Some installers describe themselves as “FENSA-approved” rather than “FENSA-registered”. These terms are not interchangeable. FENSA registers installers; it doesn’t “approve” them in a separate sense. If an installer says “approved” but can’t give you a registration number, ask more questions.

Similarly, “FENSA-accredited” and “FENSA-certified” aren’t official FENSA terms. The correct wording is “FENSA-registered installer” and it applies specifically to the company (or trading name), not to individual staff, subcontractors or products.

If you see any of this alternative language on quotes or websites, cross-check the installer name against the FENSA installer directory. If they appear, the terminology is just marketing shorthand. If they don’t, the language is misleading.

Frequently asked questions

The questions we get asked most often about FENSA by homeowners across Hampshire, Surrey and Berkshire.

Q. What is a FENSA certificate?

A. A FENSA certificate is a document confirming that replacement windows or doors installed at a property meet Building Regulations. It’s issued within 30 days of installation by a FENSA-registered installer and is registered against the property address permanently.

Q. Do I legally need a FENSA certificate?

A. Not to install windows, but you will need one to sell the property. Without a FENSA certificate for windows installed in the past 10 years, buyers’ solicitors will usually require retrospective indemnity insurance before the sale can complete.

Q. How much does a FENSA certificate cost?

A. Nothing, if your installation is done by a FENSA-registered installer. The cost is built into the installation quote. Retrospective certification through Building Control can cost several hundred pounds if a certificate was never issued at the time.

Q. How long does a FENSA certificate last?

A. The certificate lasts the lifetime of the installation and stays registered against the property address. When you sell, the certificate transfers to the new owner as part of the property documentation.

Q. What happens if I don’t have a FENSA certificate when selling?

A. Buyers’ solicitors typically ask for retrospective indemnity insurance, which costs £150 to £400. This covers the risk of Building Control enforcement, but doesn’t cover the quality of the work itself.

Q. Can any window installer issue a FENSA certificate?

A. No. Only companies registered with FENSA can issue certificates. A registered installer has a unique registration number that can be verified on the FENSA installer directory at fensa.org.uk.

Q. Is FENSA the only competent persons scheme?

A. No. CERTASS and BM TRADA are other competent persons schemes for windows and doors in England and Wales. FENSA is the most widely recognised, but a certificate from any of them fulfils the same legal purpose.

Get a quote from a FENSA-registered installer

Cristal Windows is a family-run company based in Fleet, supplying and installing across Hampshire, Surrey and Berkshire. We have been members of the Glass and Glazing Federation for 34 years, we are FENSA registered (number [NUMBER TO CONFIRM]) and a Which? Trusted Trader, and every eligible installation we complete is registered with FENSA within 30 days.

If you would like to talk through a window or door replacement, request a free, no-obligation quote and we will arrange a site survey at a time that suits you.