FENSA vs Certass vs Building Control: Which Self-Certification Route for Windows?

Every window replacement in England and Wales must be certified as compliant with Building Regulations. You have three routes to that certificate: FENSA, Certass, or a Building Control application through your local authority. The route you pick determines how much you pay, who inspects the work, and — most critically — what happens when you try to sell your home.

Why certification matters

Since 1 April 2002, all replacement glazing in England and Wales has been “notifiable work” under the Building Regulations. That means the local authority must be told about it. The three routes are simply different ways of fulfilling that notification.

If you replace windows without any certification, two things happen:

1. The local authority can serve an enforcement notice requiring you to prove compliance (or remove the windows) — this is rare but has legal weight
2. Your buyer’s solicitor will flag the missing certificate during the conveyancing process, and you will be asked to pay for an “indemnity insurance” policy — typically £100-£300 — or provide a retrospective certification

The conveyancing issue is the one most homeowners encounter. A missing FENSA or Certass certificate on a replacement window installed after 2002 is a standard search result that solicitors flag on almost every transaction.

FENSA: the market leader

FENSA (Fenestration Self-Assessment Scheme) was established in 2002 as the first Competent Person Scheme for glazing. It is by far the largest, with over 10,000 registered installers.

How FENSA works

1. You hire a FENSA-registered installer
2. The installer self-certifies that the work meets Building Regulations
3. FENSA issues a certificate to the householder
4. FENSA notifies the local authority on your behalf
5. FENSA inspects a sample of the installer’s work (approximately 2% of jobs) to verify compliance

Cost

FENSA charges the installer a notification fee per job — typically £25-£50, which the installer passes on to you. There is no separate charge for the certificate.

What FENSA covers

• Replacement windows and doors in existing dwellings
• Replacement rooflights
• Conservatory windows (where the conservatory has building regulation approval)

What FENSA does not cover

• New build windows (these are certified under the overall building control for the new dwelling)
• Windows in commercial premises (unless they are a dwelling)
• Structural alterations (such as making a window opening wider — this needs a full Building Control application)
• Properties in conservation areas or listed buildings where planning permission is separate from Building Regulations

The FENSA certificate and selling your home

A FENSA certificate is accepted by every major conveyancing solicitor and mortgage lender in England and Wales as proof that the windows comply with Building Regulations. When you sell, your solicitor will request the FENSA certificate from the Land Registry’s “Local Land Charges” search. If you have misplaced your certificate, FENSA will reissue it for £25.

Certass: the alternative

Certass (Certification and Self-Assessment Scheme) is the second Competent Person Scheme for glazing. It operates on the same legal basis as FENSA — installers self-certify their work and the scheme notifies the local authority.

How Certass works

Same process as FENSA: hire a Certass-registered installer, they self-certify, Certass issues a certificate and notifies the local authority.

What Certass offers that FENSA does not

• Glazing assets: A guarantee scheme that covers the installation for 10 years, backed by an insurance policy. This goes beyond FENSA’s compliance certificate — it is a warranty against defects.
• Thermal regulations certification: Certass specifically certifies that the glazing meets Part L thermal requirements.

Cost

Similar to FENSA: the installer pays a notification fee of £25-£50 per job, which is passed on.

The Certass certificate and selling your home

Certass certificates are accepted by the same conveyancing processes as FENSA. The key difference is that Certass also records the guarantee status. A buyer’s solicitor will see both that the work was Building Regulations compliant and that the guarantee is still active (or expired).

Local Building Control: the fallback

If your installer is not registered with FENSA or Certass, or if the work falls outside their scope, you must submit a Building Control application to your local authority.

How it works

1. You (or your installer) submit a Building Notice or Full Plans application to the local authority before the work starts
2. The local authority sends a Building Control Officer to inspect the work
3. If the work complies, the local authority issues a Completion Certificate
4. If it does not comply, the officer will issue a list of remedial work

Cost

Building Control fees vary by local authority but are typically £150-£350 for a single window replacement and £250-£600 for a full house replacement. This is significantly more than the FENSA/Certass notification fee.

When you are forced to use Building Control

• You are using an installer who is not FENSA or Certass registered (a DIY installation, for example)
• The work involves structural alterations (widening a window opening, converting a window to a door)
• The property is listed and the work requires separate listed building consent
• You are in Scotland or Northern Ireland (where FENSA and Certass do not operate — see below)
• The local authority has rejected a FENSA or Certass certification for technical reasons

The completion certificate and selling your home

A Building Control Completion Certificate is the most authoritative proof of compliance. However, unlike FENSA, it does not automatically appear on the standard local authority searches. Your solicitor will need to specifically request it from the building control department. If the work was done years ago and the local authority’s records are incomplete, obtaining a retrospective certificate can be difficult and may require a “regularisation” application (effectively asking the council to inspect old work), which costs £200-£500.

Scotland and Northern Ireland

FENSA and Certass operate in England and Wales only.

Scotland

Window replacements in Scotland must comply with the Building Standards Technical Handbook. There is no Competent Person Scheme equivalent. All notifiable work must be certified either through a “Verifier” (the local authority building standards team) or through an “Approved Certifier of Construction” — a separate Scottish scheme. The process is more formal and more expensive than FENSA.

Northern Ireland

Building Regulations in Northern Ireland are enforced by the district council. There is no self-certification scheme. All window replacements that are not “like-for-like” require a Building Control approval application.

FENSA vs Certass vs Building Control: head-to-head

Feature	FENSA	Certass	Building Control
Cost	£25-£50 (per job)	£25-£50 (per job)	£150-£600
Inspection	2% sample (random)	2% sample (random)	Mandatory on every job
Certificate type	Compliance only	Compliance + guarantee	Completion certificate
Who can use it	FENSA-registered installer	Certass-registered installer	Anyone (via application)
DIY installations	Not covered	Not covered	Accepted (with application)
Structural work	Not covered	Not covered	Required
Scotland	Not applicable	Not applicable	Required
Selling your home	Standard certificate	Standard certificate	Requires specific request

The guarantee gap

FENSA certificates confirm compliance at the date of installation. They are not a warranty. If your window develops a defect two years after installation, FENSA will not help — you must go back to the installer.

Certass’s Glazing Assets scheme provides a 10-year guarantee that is insurance-backed. If the installer goes out of business, the insurance policy covers the cost of remedial work.

Building Control provides no guarantee at all — only a certificate that the work was compliant on the day of inspection.

Practical advice: If your FENSA installer offers an insurance-backed guarantee (and most do), take it. It costs £50-£100 extra and covers you against the installer going bust. Without it, a dissolved company means you have no warranty.

How to check your existing certificates

If you are selling your home and need to prove your windows were certified:

1. FENSA: Search at fensa.org.uk using your postcode. FENSA also registers certificates with the Land Registry.
2. Certass: Search at certass.co.uk. You will need the installer’s name or your postcode.
3. Building Control: Contact your local authority’s building control department. You will need the approximate date of installation and the property address.

If you cannot find any certificate for work done after 2002, you can apply for a retrospective FENSA or Certass assessment (if the installer was registered at the time) or a Building Control regularisation certificate (if the work was done without certification).

Summary

• Use a FENSA or Certass installer for straightforward window replacements — the cost is built into the installation, and the certificate protects your sale
• Choose Certass if the installer offers the Glazing Assets insurance-backed guarantee
• Use Building Control if the installer is not registered, if the work is structural, or if you are doing the work yourself
• In Scotland and Northern Ireland, Building Control is the only route
• Always keep the certificate — it will be requested when you sell, and a missing certificate costs £100-£300 in indemnity insurance