WIAPS Certificate Explained: What Sellers Need to Know

When you sell a property in England or Wales, the buyer's solicitor will check whether any replacement windows, doors, or roof windows have the correct Building Regulations sign-off. One of the documents they may encounter — or ask about — is a WIAPS certificate.

WIAPS is less well known than FENSA, but it serves exactly the same purpose. This guide explains what WIAPS is, how it compares to other window certification schemes, and what to do if your property has replacement windows without the right documentation.

What is WIAPS?

WIAPS stands for the Window Installation Assurance Scheme. It is a competent person scheme authorised by the UK government under the Building Regulations. The scheme is operated by the British Board of Agrément (BBA), one of the UK's most established construction certification bodies.

When a WIAPS-registered installer fits replacement windows, external doors, or roof windows, they can self-certify that the work complies with Part L (conservation of fuel and power) of the Building Regulations. This means the homeowner does not need to arrange a separate inspection from the local authority's building control department. The installer notifies the local authority on the homeowner's behalf, and the homeowner receives a WIAPS certificate confirming compliance.

The scheme covers installations in England and Wales. Scotland and Northern Ireland have separate building standards regimes with their own compliance processes.

How WIAPS differs from FENSA and other schemes

WIAPS is one of several competent person schemes approved by the government for window and door installations. The most widely recognised is FENSA (Fenestration Self-Assessment Scheme), which is managed by the Glass and Glazing Federation. Other approved schemes include CERTASS and, for certain types of work, schemes managed by bodies such as NAPIT and Stroma.

All of these schemes serve the same legal function: they allow registered installers to self-certify that their work meets the Building Regulations. A certificate from any government-authorised competent person scheme carries the same legal weight. The buyer's solicitor and mortgage lender are required to accept a WIAPS certificate on the same basis as one from FENSA or CERTASS.

The key differences between the schemes are practical rather than legal:

From a conveyancing perspective, the important point is that any one of these routes provides valid proof of compliance. If your windows have a WIAPS certificate, you do not also need a FENSA certificate or building control sign-off. One valid certificate is sufficient.

Which installations need certification?

Since 1 April 2002, the replacement of windows, external doors, and roof windows in England and Wales has been classified as building work that must comply with the Building Regulations. Specifically, the work must meet Part L (conservation of fuel and power), which sets minimum thermal performance standards for replacement glazing.

The regulations require that replacement glazing achieves a minimum Window Energy Rating (WER) of band C or a centre-pane U-value of 1.4 W/m²K or better. They also address ventilation requirements and, where relevant, means of escape in the event of fire.

Compliance must be demonstrated through one of the following:

• A certificate from a competent person scheme such as WIAPS, FENSA, or CERTASS
• A completion certificate from the local authority's building control department

If none of these documents exists for windows replaced after April 2002, the installation is technically non-compliant. This is the situation that creates problems during a property sale. For a comprehensive overview of all the paperwork you may need, see our guide on property certificate packs.

Installations that do not need certification

• Windows installed before 1 April 2002. The Building Regulations requirement only applies to installations from this date onwards. No certificate of any kind is needed for earlier work.
• Like-for-like repairs. Repairing an existing window (for example, replacing a broken pane within the original frame) is maintenance, not building work, and does not require sign-off.
• New-build properties. Windows fitted as part of the original construction are covered by the building control sign-off for the new build. A separate WIAPS or FENSA certificate is not required.

How to check if you have a WIAPS certificate

If you know your replacement windows were installed by a WIAPS-registered company, the certificate should have been sent to you within a few weeks of the installation. However, certificates are easily misplaced, particularly if the windows were fitted many years ago or by a previous owner.

To trace a WIAPS certificate:

1. Contact the WIAPS scheme directly. The scheme is managed by the BBA. You can reach them by telephone or through their website. Provide your property address and the approximate date of installation. If a record exists, they can issue a duplicate certificate.
2. Contact the installer. If you know which company fitted the windows, they may hold records of the installation and can confirm whether it was registered with WIAPS. They may also be able to help you obtain a replacement certificate from the scheme.
3. Check other databases. If you are unsure which scheme the installer used, also search the FENSA database at fensa.org.uk and the CERTASS database at certass.co.uk. The installer may have been registered with a different competent person scheme.
4. Contact your local authority. If no competent person scheme certificate exists, the installer or a previous owner may have arranged a building control inspection directly. Your local authority building control department should hold records of any completion certificates issued for your address.

If none of these searches returns a result, it is likely that the installation was never certified. In that case, you will need to resolve the compliance gap before selling.

What to do if you have no WIAPS certificate (or any other certificate)

If your replacement windows were installed after 1 April 2002 and you cannot find a WIAPS certificate, FENSA certificate, CERTASS certificate, or local authority completion certificate, you have two main options. Both are well-established routes that conveyancers deal with regularly.

Option 1: Indemnity insurance

Indemnity insurance is the most commonly used solution for older window installations without Building Regulations certification. It is a one-off insurance policy that protects the buyer and their mortgage lender against the financial risk of the local authority taking enforcement action over the non-compliant installation.

Key points:

• The cost is typically £30 to £100 as a one-off premium, depending on the property value and insurer
• The policy lasts indefinitely and transfers automatically to future owners
• Your solicitor arranges the policy, usually within 24 to 48 hours
• The seller normally pays for the policy as part of the sale
• Critical condition: you must not have contacted the local authority about the windows before the policy is in place. If building control has been approached, most insurers will refuse cover

Indemnity insurance is accepted by the vast majority of mortgage lenders and is the standard solution recommended by conveyancers for window installations completed more than 12 months ago. For a fuller explanation of when this type of cover applies, see our guide on indemnity insurance.

Option 2: Regularisation certificate from the local authority

If you prefer formal proof of compliance — or if indemnity insurance is unavailable because you have already contacted the local authority — you can apply for a regularisation certificate. This is retrospective Building Regulations approval under Section 36 of the Building Act 1984.

The process involves:

1. Submitting a regularisation application to your local authority building control department
2. Paying the application fee, typically £250 to £500 depending on the council
3. A building control officer visiting the property to inspect the windows
4. If the windows meet the required standard, the council issues a regularisation certificate

The main drawback is time. The process can take four to eight weeks, and there is a risk that the windows may not pass inspection — for example, if the thermal performance is below the required standard. If the windows fail, you may need to carry out remedial work, which adds further cost and delay.

WIAPS vs FENSA vs building control: comparison for sellers

The following table summarises the three main routes to Building Regulations compliance for replacement windows and how they compare during the conveyancing process:

The practical takeaway is that all three routes are equally valid for conveyancing purposes. If you have a WIAPS certificate, it is just as good as a FENSA certificate. If a buyer's solicitor queries it, your solicitor can point them to the GOV.UK list of approved competent person schemes, which confirms WIAPS is fully authorised.

The conveyancing process for window compliance

Understanding how window compliance fits into the conveyancing timeline helps you prepare effectively and avoid delays.

Before you list

Check whether you have WIAPS, FENSA, CERTASS, or building control certificates for all replacement windows installed after April 2002. If certificates are missing, decide whether to pursue indemnity insurance or regularisation. Preparing this documentation in advance is one of the most effective things you can do to speed up the sale. For a complete list of documents you should gather, see our guide on property certificate packs.

When the buyer's solicitor raises enquiries

The buyer's solicitor will review the TA6 Property Information Form, which requires you to disclose any building work and whether certificates were obtained. If you declare that replacement windows lack a certificate, they will raise a pre-contract enquiry. If you already have indemnity insurance or a regularisation certificate ready, the enquiry can be answered immediately.

Mortgage lender requirements

Most mortgage lenders follow the UK Finance Mortgage Lenders' Handbook, which requires the buyer's solicitor to confirm that replacement windows have proper Building Regulations compliance. A WIAPS certificate satisfies this requirement. If no certificate exists, lenders will typically accept indemnity insurance for installations completed more than 12 months ago.

Exchange and completion

The window compliance issue must be resolved before exchange of contracts. The buyer's solicitor cannot advise their client to proceed — and the mortgage lender cannot release funds — with an outstanding Building Regulations compliance issue. Once a valid certificate or indemnity policy is provided, this item is cleared and does not cause further delay.

Your duty of disclosure as a seller

As a seller, you have a legal obligation to answer questions on the TA6 Property Information Form honestly. Section 6 of the form asks specifically about building work and whether relevant consents and certificates were obtained. Deliberately concealing the absence of a window certificate could constitute misrepresentation, giving the buyer grounds to seek compensation after completion.

The correct approach is to disclose the situation and provide evidence that it has been resolved — whether through a WIAPS certificate, an alternative competent person scheme certificate, indemnity insurance, or a regularisation certificate. For more on your obligations, see our guide on seller duty of disclosure.

Window guarantees are not a substitute for a WIAPS certificate

A common source of confusion is the difference between a window guarantee and a WIAPS certificate. Many installers provide commercial guarantees or warranties covering defects in the product or workmanship for a period of 10 to 20 years. These guarantees are valuable but serve a completely different purpose.

A guarantee is a commercial document that says nothing about Building Regulations compliance. It cannot substitute for a WIAPS certificate, FENSA certificate, or building control sign-off during conveyancing. If your windows have a guarantee but no competent person scheme certificate, you still have a compliance gap that needs to be addressed. For a detailed explanation of how to handle this situation, see our guide on window guarantees without FENSA registration.

Practical steps for sellers

1. Check all competent person scheme databases for your property address. Search WIAPS (via the BBA), FENSA (fensa.org.uk), and CERTASS (certass.co.uk). This takes a few minutes and may reveal that certification already exists.
2. Contact the installer if the databases show no record. Ask whether they registered the work and, if so, under which scheme. They may be able to arrange a duplicate certificate.
3. Check with your local authority building control department for any completion certificates. Only do this if you have already decided against indemnity insurance, as contacting the council can invalidate the insurance option.
4. Speak to your solicitor before taking any action. If no certificate exists and you are planning to sell, your solicitor will advise whether indemnity insurance or regularisation is the better route for your circumstances.
5. Assemble all window documentation — certificates, guarantees, insurance policies, and installation invoices — and include them in your property certificate pack so everything is ready for the buyer's solicitor.

Sources

• WIAPS (Window Installation Assurance Scheme) — operated by the British Board of Agrément (BBA)
• FENSA (Fenestration Self-Assessment Scheme) — fensa.org.uk
• CERTASS (Competent Person Scheme for windows and doors) — certass.co.uk
• GOV.UK — Building Regulations: Approved Document L (Conservation of fuel and power)
• GOV.UK — Competent person schemes: current schemes and types of work they cover
• Building Act 1984, Section 36 (Enforcement of building regulations) — legislation.gov.uk
• The Building Regulations 2010 (SI 2010/2214) — legislation.gov.uk
• UK Finance Mortgage Lenders' Handbook — ukfinance.org.uk

Frequently asked questions