FENSA Regulations: What You Need to Know Before Replacing Windows

FENSA window regulations affect every homeowner in England and Wales who replaces windows or external doors. The Fenestration Self-Assessment Scheme ensures that replacement glazing meets Building Regulations without requiring a separate inspection by your local authority. Getting this wrong can cause real problems when you come to sell your property, so understanding the FENSA process, your installer’s responsibilities and how to verify their registration is essential before any window replacement project begins.

What Are FENSA Regulations for Window Replacement?

FENSA is a government-authorised scheme that allows registered window installers to self-certify that replacement windows, doors and roof lights meet building regulations without the homeowner needing to involve their local council. When you use a FENSA-registered installer, they notify building control on your behalf and issue a certificate confirming the work is compliant.

If your installer is not FENSA-registered, you must apply to your local authority for building regulations approval before work begins, which costs £200 to £500 in inspection fees and can delay the project. Without either a FENSA certificate or a building control completion certificate, you may face problems when selling your home, as solicitors routinely flag missing window certificates during conveyancing searches.

What Is FENSA and Why Does It Exist?

FENSA stands for Fenestration Self-Assessment Scheme. It is a Competent Person Scheme authorised by the UK Government (specifically the Department for Levelling Up, Housing and Communities) that allows registered window and door installers to self-certify that their work complies with Building Regulations.

When you replace windows or external doors, the work must comply with Part L (conservation of fuel and power), Part F (ventilation), Part N (glazing safety) and Part K (protection from falling) of the Building Regulations. Without FENSA registration, the installer would need to notify the local authority building control department before starting work, and a building control officer would need to inspect and sign off the installation.

FENSA streamlines this process. A FENSA-registered installer self-certifies compliance, and FENSA notifies the local authority on the homeowner’s behalf. A compliance certificate is then issued and registered with the local authority, creating an official record that the work was done to the required standard.

What Happens When You Use a FENSA-Registered Installer

When you hire a FENSA-registered company to replace your windows, the following process should occur:

• Survey and quotation: The installer surveys your property and provides a quote specifying compliant window products
• Installation: Windows are fitted to FENSA standards, including correct glass specification, trickle vents (where required), safety glazing and fire escape compliance
• Notification: The installer registers the completed work with FENSA within 30 days
• Certificate issued: FENSA issues a compliance certificate confirming Building Regulations compliance
• Local authority notification: FENSA notifies your local council’s building control department automatically

The homeowner should receive the FENSA certificate within a few weeks of installation. Keep this certificate with your property deeds, as it will be needed when you sell the property.

What If Your Installer Is Not FENSA Registered?

If your window installer is not registered with FENSA (or the alternative scheme, CERTASS), they cannot self-certify compliance with Building Regulations. This means:

• You must apply to your local authority building control department before the work starts
• A building control officer will inspect the installation during and after the work
• You will pay a building control fee, typically GBP 200-400
• The process takes longer and involves scheduling inspections

If you use a non-registered installer and do not apply to building control, you will have no certificate proving compliance. This creates a significant problem when selling your property.

The Consequences of No FENSA Certificate

When you sell your property, the buyer’s solicitor will request evidence that any replacement windows comply with Building Regulations. Without a FENSA certificate or building control completion certificate, you face several potential issues:

• Retrospective building control application: You can apply to your local authority for a regularisation certificate. This involves a building control officer inspecting the existing installation, which may or may not pass. The fee is typically GBP 300-500, significantly more than the original building control fee would have been.
• Indemnity insurance: Some solicitors accept an indemnity insurance policy (costing approximately GBP 60-150) instead of a certificate. However, this does not confirm that the windows actually comply; it simply provides insurance against enforcement action.
• Buyer negotiation: Buyers may demand a price reduction to cover the cost and uncertainty of non-compliant windows, or they may withdraw from the sale entirely.
• Mortgage issues: Some mortgage lenders may flag non-certified window replacements as a concern, particularly on leasehold properties.

The message is clear: always use a FENSA or CERTASS registered installer, or apply to building control yourself if using a non-registered tradesperson.

FENSA and Trickle Vent Requirements

Since June 2022, updated Approved Document F (ventilation) has made trickle vents mandatory in most replacement windows in England. This is now a key element of FENSA compliance.

The basic rules are:

• If the existing windows being replaced already have trickle vents, the new windows must have trickle vents of at least the same equivalent area
• If the existing windows do not have trickle vents, the new windows must have trickle vents fitted unless a specific ventilation assessment demonstrates they are not needed
• The minimum equivalent area for trickle vents is 5,000mm2 for a small room (less than 10m2) and 8,000mm2 for a habitable room (bedroom, living room)
• Wet rooms (bathrooms, kitchens) may require additional background ventilation depending on the existing ventilation provision

Some homeowners object to trickle vents on aesthetic grounds or because they worry about draughts. However, the vents are closable (you can shut them in extreme weather) and play an important role in maintaining indoor air quality, particularly in well-insulated homes with good draught-proofing. A FENSA-registered installer should explain the trickle vent requirements during the survey and include them in the quotation.

How to Check If an Installer Is Genuinely FENSA Approved

Unfortunately, some unregistered installers claim to be FENSA approved when they are not. Verifying registration takes only a few minutes and could save you significant problems later.

• Search the FENSA website: Visit fensa.org.uk and use the “Find an Installer” search tool. Enter the company name or postcode to check their current registration status.
• Ask for the FENSA registration number: Every registered company has a unique number. Request this and cross-check it on the FENSA website.
• Check the valid dates: FENSA registration must be renewed annually. Confirm that the registration is current, not expired.
• Request evidence of insurance: FENSA-registered companies must hold public liability insurance and employer’s liability insurance. Ask to see current certificates.

If the company is registered with CERTASS instead of FENSA, this is equally valid. CERTASS is the other government-authorised Competent Person Scheme for glazing installations and provides the same self-certification and local authority notification function. Check CERTASS registration at certass.co.uk.

What FENSA Does Not Cover

It is important to understand the limits of FENSA certification:

• Quality of workmanship: FENSA certifies Building Regulations compliance, not the quality of the installation. Poorly fitted windows that technically meet thermal requirements can still have issues with alignment, operation and weatherproofing.
• Product warranty: The FENSA certificate is separate from the manufacturer’s product guarantee and the installer’s workmanship guarantee. Ensure you have all three.
• Repairs and maintenance: Replacing a single sealed unit (the glass) within an existing frame does not require FENSA notification. Only the replacement of complete window or door units triggers the requirement.
• Internal alterations: Adding secondary glazing or replacing internal doors does not fall under FENSA.
• Listed buildings: FENSA compliance does not override the need for Listed Building Consent if your property is listed. Both requirements must be met independently.

For the best experience with replacement double glazing, choose an installer who is both FENSA registered and a member of an industry body such as the Glass and Glazing Federation (GGF). This provides additional protection through deposit guarantees, mediation services and insurance-backed warranties.

When planning your window replacement, consider combining it with other energy efficiency improvements such as wall insulation and a boiler upgrade for the greatest impact on your energy bills. Get a free quote to explore your options.

Frequently Asked Questions

How much does a FENSA certificate cost?

The cost of FENSA certification is included in the installer’s quote. You should not be charged separately for the certificate. The installer pays a registration fee to FENSA (currently a small per-installation fee), and this is factored into their standard pricing. If an installer asks you to pay extra for a FENSA certificate, this is unusual and worth querying.

Can I get a retrospective FENSA certificate for windows installed without one?

No. FENSA cannot issue certificates retrospectively. If your windows were installed without FENSA or CERTASS notification, your only options are to apply to your local authority for a regularisation certificate (which involves an inspection and a fee of GBP 300-500) or to obtain an indemnity insurance policy. The regularisation route is preferable because it provides actual confirmation of compliance.

Does FENSA apply in Scotland and Northern Ireland?

FENSA operates in England and Wales only. Scotland has its own building warrant system under the Building (Scotland) Act 2003, and Northern Ireland has a separate regime under the Building Regulations (Northern Ireland) 2012. In Scotland, replacement windows generally require a building warrant application to the local authority. In Northern Ireland, the requirements are similar to England and Wales, with CERTASS NI providing a Competent Person Scheme.

Is FENSA the same as CERTASS?

No, they are two separate organisations, but both are government-authorised Competent Person Schemes for window and door installation. Both provide the same function: allowing registered installers to self-certify Building Regulations compliance and automatically notifying the local authority. A certificate from either scheme is equally valid for property sales and mortgage applications.

Do I need FENSA for conservatory windows?

If the conservatory is an exempt structure (ground floor, under 30m2, with a separating wall and door between it and the main house), replacing windows within the conservatory may not require Building Regulations compliance. However, if the separating wall and door have been removed, the conservatory is no longer exempt and window replacements must comply with Part L, requiring FENSA notification. Full conservatory roof replacements have their own compliance requirements.