FENSA, Certass and What the Certificate Actually Proves

Last Updated on September 8, 2026

Replacing a window is Building Regulations work. That single fact is the foundation of everything commercial in this trade, and most installers sell it badly or not at all.

The three routes, and the one the trade uses

GOV.UK sets out three ways to satisfy Building Regulations on replacement windows and doors: apply to local authority building control, use a private registered building control approver, or use an installer registered with a competent person scheme, in which case, in GOV.UK’s own words, you do not need to get approval yourself.

That third route is the trade’s entire commercial advantage over an unregistered competitor, and it is worth stating on the page in exactly those terms.

Six schemes, not two

The government publishes the authoritative list of authorised competent person schemes. We read it on 8 September 2026. The operators authorised for replacement windows and doors are:

• Blue Flame Certification
• Certass Limited
• Certsure LLP, trading as NICEIC
• Fensa Limited
• NAPIT Registration Limited
• Assure Certification Limited

ELECSA does not appear on the current list; its functions sit under Certsure. If you are renewing a scheme membership without shopping around, you have four more options than the trade press generally implies.

The disagreement about what the certificate is called

This is the sharpest published dispute in the sector, and both sides are primary sources.

FENSA sells homeowners a replacement copy of what it calls a FENSA certificate for £30 including VAT, describing it as proof the work complies with Building Regulations and is registered with the local council.

Certass publishes, in its own words, that there is no such thing as a FENSA certificate, only a Building Regulations Compliance Certificate, which can be issued by multiple competent person schemes including Certass, and that regardless of which scheme is used the certification issued is valid and serves the same purpose.

Both statements were live on 8 September 2026. The legal position is Certass’s: the document is a compliance certificate and the scheme is the issuer. The commercial position is FENSA’s, because homeowners, estate agents and conveyancers ask for it by name.

For an installer in any of the other five schemes, that is a vocabulary problem costing real jobs. The fix is not to change scheme. It is to write one paragraph on your site explaining which scheme you are in, that it issues a Building Regulations Compliance Certificate, and that this is the same legal document people mean when they say FENSA certificate.

What registration actually costs, per job

FENSA publishes its fee schedule in full, document FSPF 53 issue 9, dated January 2025, read on 8 September 2026.

Assessment frequency is banded: up to 25 installations a year means a minimum of one assessment, 26 to 200 means two, and above 200 it is 1 per cent of all installations.

FENSA also publishes its own worked totals, excluding VAT:

Which produces a point most should-I-join content misses entirely. At ten installations a year the true cost of compliance is about £34 a job. At three hundred it is about £4. Registration is a fixed cost that punishes low volume, and that is the actual calculation for a one-van installer deciding whether to join.

Certass publishes a £120 initial company audit fee for year one. Its page says it gives examples of monthly fees, but no monthly figures rendered on the page we read, so we cannot give you a comparison. Neither scheme publishes a current installer count.

What happens to a homeowner without a certificate

This is the argument to make, and it should be made honestly rather than as a scare.

If the installer was not registered, the homeowner has to obtain Building Regulations approval themselves, and retrospectively that is a regularisation application. Councils set their own charges and the spread is large.

That is a 2.5 times difference between two published UK council schedules for the same job, so nobody can honestly quote a national figure for what regularisation costs. Certass’s consumer site publishes a national range of £120 to £350, which does not contain the Lambeth figure we read on Lambeth’s own schedule.

Lambeth also publishes a line worth quoting to a customer weighing a cheap unregistered quote: there is no entitlement to a refund of a regularisation charge, even if the council cannot determine compliance, cannot certify the work, or the work is later removed.

The two rules being misused in this trade

Part Q, security in dwellings, applies to new dwellings only. Its 2015 edition states it does not apply to work started before 1 October 2015 and is scoped to new dwellings. An installer marketing a replacement window as Part Q compliant, as required by law, is describing an obligation that does not bind that job.

Part L is the other one. The 2026 edition of Approved Document L, volume 1 for dwellings, takes effect on 24 March 2027 for non-higher-risk building work and 24 September 2027 for higher-risk buildings. It keeps the same replacement figures as the 2021 edition with 2023 amendments: 1.4 W/m²K or Window Energy Rating band B minimum for windows, doorset band C for doors over 60 per cent glazed and band B for other doors.

So the U-value target for a replacement window does not change in 2027. An installer selling beat the 2027 regulation change is selling urgency that does not exist for replacement windows, and a customer who checks will not come back.

Where a homeowner can check

Common questions

Is a FENSA certificate a legal requirement?

No. Building Regulations compliance is the requirement. A competent person scheme certificate is one of three ways to demonstrate it, and six schemes are authorised for windows and doors. What FENSA calls a FENSA certificate is a Building Regulations Compliance Certificate, which any authorised scheme can issue.

What does it cost to join FENSA?

£267.40 excluding VAT as a one-off application, then £172 a year excluding VAT plus £2.05 per installation notified. FENSA’s own worked examples put the total at about £337.75 a year at ten installations and £1,222.75 at three hundred, all excluding VAT, read on 8 September 2026.

What if my installer was not registered?

The homeowner applies for a regularisation certificate from the local authority. Charges vary hugely: about £189 at Lancaster City Council against £476.05 at Lambeth for the same retrospective job, on schedules read on 8 September 2026, and Lambeth publishes that the charge is not refundable even if compliance cannot be certified.

Whito

Whito is an independent UK research bureau. We ask the AI engines what they recommend, then check the businesses they name against Companies House and the sector registers. Figures we publish carry the date they were checked. Companies cannot pay to appear or to rank.

See Full Bio