FENSA and Certass: Registered Window and Door Installers

Replacing windows or doors is building work, and building work has to comply with the building regulations. The two names a householder meets when hiring a glazing company, FENSA and Certass, are competent person schemes: programmes introduced by the government to allow tradespeople to self-certify that their work complies, rather than putting every job through a council building control application¹. Membership of a scheme is voluntary for the installer, and self-certification is instead of getting building regulations approval².

FENSA, the Fenestration Self-Assessment Scheme, was established in 2002 and is the scheme most households encounter first³. A FENSA registered installer self-certifies window and door installations under the Building Regulations, hands the householder a FENSA certificate, and remains subject to independent inspections³. Certass performs the same function for glazing under a separate scheme, and the certificate either scheme issues is the document a solicitor asks for when a home is sold.

What a Competent Person Scheme is, and why it exists

Competent Person Schemes were introduced by the government to allow tradespeople to self-certify that their work complies with the Building Regulations¹. Before the schemes existed, the only route was a building control application for almost any notifiable job, which meant cost and delay for households and a heavy workload for council teams. The schemes transfer the job of confirming compliance to the installer, on condition that the installer has been assessed as competent and accepts ongoing scrutiny.

An installer registered with a scheme, for example of windows or boilers, can self-certify that the work complies with building standards⁷. Official guidance for householders describes using an installer registered with a scheme, a registered competent person, as the preferred route, precisely because that person can self-certify⁸. That guidance is blunt about the alternative: installers registered with a Competent Person Scheme can self-certify that their work is compliant, and the alternative is a building control route with its own application and inspection⁹.

Membership is voluntary, and schemes have different application processes, so an installer chooses which scheme to join and there is no single central register of everyone². What a scheme buys the householder is procedural: work carried out under a Competent Person Scheme does not need notification to Building Control, because members are allowed to certify their own work and tell the council the work has been properly installed and tested¹⁰. The schemes themselves are authorised by government: authorised schemes are listed in Schedule 1 of the Building Regulations &c. (Amendment) Regulations 2015 with effect from 18 April 2015, and the last invitation for new schemes to apply took place on 10 December 2014⁶. The full list of schemes and the work types they cover is on our page on competent person schemes.

FENSA: the first scheme most homes encounter

FENSA, the Fenestration Self-Assessment Scheme, was established in 2002 and exists to self-certify window and door installations under Building Regulations³. A company registered with FENSA can self-certify compliance and present the homeowner with a FENSA Certificate, but remains subject to regular independent inspections for building regulations compliance⁴. That last part matters: registration is not a one-off badge. FENSA registered installers have made the effort to comply with the eligibility criteria of FENSA registration, have been vetted and are regularly and independently assessed⁴.

For the householder, a FENSA registered installer does three things an unregistered one cannot. It self-certifies the installation against the Building Regulations, it provides a FENSA certificate, often requested during property sales, and it offers an insurance-backed guarantee, giving peace of mind should something go wrong³. FENSA also publishes consumer guidance on spotting poor operators, including a Consumer Guide to Cowboys containing hints and tips to recognise a cowboy, and it has taken action against cowboys a number of times, with installer prosecutions listed publicly⁴.

The checks FENSA itself recommends before appointing an installer are ordinary ones: ask family and friends about satisfaction and whether they received a FENSA certificate, check references, get at least three quotes and check the quotes are like for like, get the quotes, timeframes and the FENSA certificate commitment in writing with an agreed completion date, and check the warranty and insurance cover⁴. Our page on checking an installer before signing works through this in detail.

Certass: the alternative glazing scheme

Certass is a second authorised competent person scheme covering the same territory: replacement windows and doors in homes. Because membership of any competent person scheme is voluntary and schemes have different application processes, a glazing company may be registered with FENSA, with Certass, or in some cases with both, and the householder comparing quotes will meet both names². The underlying legal position is identical whichever scheme is used: a registered installer is approved to carry out the work to comply with building regulations without involving local authority building control, and a certificate is issued on completion¹¹.

What differs between the schemes is administration rather than legal effect. Both issue a certificate recording that the installation was self-certified against the building regulations, and both operate inspection regimes over their registered installers. A useful way to think about the certificate, whichever scheme issues it, is that it is a building regulations compliance certificate for the glazing: the brand name on the paperwork reflects which scheme the installer belonged to, not a different standard of work. Our page on the Building Regulations Compliance Certificate explains what the document contains.

The parallel with other trades holds here too. HETAS, for example, describes itself as a voluntary Competent Persons Scheme for installers to sign up to should they wish to do so, which is the same structural position Certass and FENSA occupy for glazing¹². None of these schemes is a regulator with power over the whole industry; each is a membership organisation authorised by government to self-certify a defined range of work, and enforcement over building work itself stays with building control.

What the certificate shows and why conveyancers request it

A FENSA or Certass certificate is the record that a registered installer self-certified the installation as compliant with the building regulations on the date shown. It is often requested during property sales because it is the simplest evidence a seller can produce that glazing work was done legally³. When a buyer's solicitor conducts conveyancing searches, a window or door replaced without either a certificate or a building control approval is a gap in the property's compliance history, and gaps raise questions that delay transactions.

The certificate also says something about who did the work. FENSA registered installers have been vetted and are regularly and independently assessed, so the certificate implies the job was done by a business that accepted ongoing scrutiny rather than a one-off check⁴. It is not, however, a guarantee of workmanship in itself, and it is not a warranty: those protections come from the installer's own warranty and the insurance-backed guarantee described later on this page.

There is a timing discipline behind the paperwork. In the electrical equivalent of the same system, the competent person must send a self-certification certificate to the local authority within 30 days of the works' completion, and the client must receive both a copy of the self-certification certificate and the test certificate¹³. Glazing schemes operate on the same principle: the installer registers the completed job with the scheme, and the certificate follows. A householder whose certificate has not arrived some weeks after completion is entitled to chase it, because without it the proof of compliance sits with the installer rather than with the home.

Two routes to compliance: self-certification or building control

Every notifiable replacement window or door installation goes down one of two routes. The first is the registered installer route: the installer is approved to carry out the work to comply with building regulations without involving local authority building control, and a certificate is issued on completion¹¹. The second is the building control route, used when the installer is unregistered or the work is a DIY job: approval can be sought from the relevant Building Control Body, either the local authority or a registered building control approver, who will check compliance and issue a certificate of compliance if satisfied¹⁴. Welsh Government guidance for doors and windows sets out the same pair of options¹⁵.

For work that is not higher risk, the householder or installer choosing the building control route can pick either the local authority's building control department or a private registered building control approver¹⁶. The cost and the waiting fall on whoever commissions the work, which is why the registered installer route exists. An installer who is not in an approved Competent Person scheme will not be able to self-certify that their work is compliant¹⁷.

The same fork in the road appears across every home energy technology, which is why it is worth understanding once:

• Electrical work: a Building Regulations application to Building Control is needed if the electrician is not registered as a competent person or if the work is done by the householder¹⁸.
• Gas appliances: a registered installer with the relevant competencies should be able to self-certify the work without the need for close involvement of building control¹⁹.
• Heat pumps: an installer not registered as a competent person must, before work begins, either notify the local authority or arrange for a registered building control approver to oversee the work²⁰.
• Solar PV: installers who are members of a relevant competent person scheme can self-certify, avoiding separate building regulations approval²¹.
• Solid fuel appliances: an application to the Local Authority Building Control is needed prior to installation if the work is done by the householder or by an installer not registered with a scheme covering that installation, though where the building is no more than three storeys and the installer is HETAS registered, a Building Control Service need not be involved²².
• Wind turbines: self-certification depends on the installer being a member of the competent person scheme listed against the relevant row of Schedule 3 of the Building Regulations²⁴.

The practical difference for a household is that the registered route bundles compliance into the installation price, while the building control route adds an application, a fee and an inspection to the same job.

The 1% inspection rate and the price of failing assessment

Registration is maintained by sampling. FENSA inspections are normally carried out on 1% of each business's installations, subject to a minimum of 2 per year and a maximum of 100 installations inspected per business per year⁴. A sampled job is inspected against the compliance criteria, and the majority of installations inspected do meet them⁴. That is a sampling regime, not a guarantee: 1% means most individual jobs are never looked at by the scheme, and the certificate a householder holds reflects the installer's declaration backed by the threat of inspection rather than a check of that specific job.

Other schemes sample at different rates, which shows the figure is a policy choice rather than a physical constant. The ECO2 technical monitoring requirement is that 5% of installations are inspected²⁵, and under ECO4, approved innovation measures are subject to technical monitoring of 50% of installations²⁶. Glazing sits at the lighter end of that spectrum.

When an inspection does find a problem, the consequences are firm. FENSA states its position without qualification:

Companies that are found to fail inspections will be assessed more often, in line with guidance from the Communities and Local Government Department, so a business that cuts corners moves onto a tighter inspection schedule rather than simply paying a fee and continuing⁴. For the householder, the rectification requirement is the operative protection: sub-standard work found by the scheme must be put right. If a dispute over quality is not resolved through the installer or the scheme, the escalation routes on our page about complaining about an installer apply, and building control retains its own enforcement powers over non-compliant work.

Insurance-backed warranties and the protection that attaches

Domestic glazing installers that are registered with a competent person scheme like FENSA are legally obliged to provide warranty insurance to cover the installation should the company cease to trade within the life of the warranty⁴. This is the insurance-backed guarantee, and it is the piece of protection that outlives the company: a FENSA registered installer offers one as standard, giving peace of mind should something go wrong³. More generally, official guidance confirms that with a Competent Person Scheme registered installer, the householder is given financial protection to cover the event of non-compliant work being found where the installation company has gone out of business⁹.

What the guarantee covers is the installation, not the products. If the glazing business folds, the insurance stands behind the workmanship claim for the warranty period, so a fault traced to how the windows were fitted remains claimable. It does not cover the glass units or frames themselves, which are the manufacturer's warranty, and it does not extend the length of cover beyond what was issued. Our page on insurance-backed guarantees sets out what to check on the policy document, and the page on what happens when an installer goes bust covers deposits and unfinished work.

The protection also depends on the insurer behind the guarantee, which is a dependence worth naming: the householder's recourse runs to an insurance company, not to the scheme and not to the installer. Checking the warranty and insurance cover before appointing an installer is one of the checks FENSA itself recommends⁴.

England and Wales: where the schemes reach, and where they stop

The self-certification scheme system operates in England and Wales⁵. That territorial limit is stated in a government consultation on reforming consumer protection for home upgrade schemes, which also notes that the wider system reforms set out in that document primarily apply to England only⁵. So a FENSA or Certass certificate is evidence of compliance under the building regulations that apply in England and Wales, and the same paperwork has no standing under the separate arrangements that handle building standards in Scotland and Northern Ireland. Householders there deal with different systems, covered on our pages about installers in Scotland and installers in Northern Ireland.

Even within England and Wales, guidance for particular technologies can be nation-specific. Planning Portal guidance on the Microgeneration Certification Scheme states that the guidance relates to the planning regime for England and that the policy in Wales may differ²⁵. The Microgeneration Certification Scheme is the government-endorsed route for finding certified installers of renewables such as solar, and official council guidance on solar panels directs householders to it and to getting at least three quotes from reputable installers²⁶. It is a different register from FENSA and Certass, covering different work, as our page on MCS certified installers explains.

There are also limits of scope rather than geography. A glazing scheme certifies building regulations compliance for replacement windows and doors; it does not certify thermal performance beyond what the regulations require, it does not rank installers, and it does not adjudicate every dispute. Where a scheme cannot resolve a matter, the local authority building control team remains the body with enforcement power over the building work itself.

What registration does, and does not do, for energy independence

Windows and doors sit on the fabric side of household energy independence. They generate nothing, so glazing registration contributes to independence indirectly: compliant replacement glazing is the building regulations' mechanism for holding the thermal envelope together, and the certificate is the proof that the work met the standards in force at the time. Those standards are not static. The Welsh Government consulted in 2025 on changes to Approved Document L Volume 1, the document governing the conservation of fuel and power in dwellings, which is the regime replacement glazing in Wales is measured against²⁰. Tighter documents mean each successive replacement does more to cut the heat a home loses.

The dependence that remains is worth stating plainly. A household that hires a registered installer hands the certification of its own home to that installer and, behind them, to a membership organisation sampling 1% of jobs and to an insurer behind the guarantee. The certificate is only as good as the inspection regime and the records that back it, and the thermal benefit is only as good as the installation. What registration removes is the dependence on a council application for every job, and the risk of an uncompliant, undocumented alteration surfacing years later at the point of sale. For the wider picture of how installer choices shape a home's self-sufficiency, see installers and energy independence, and for the full landscape of hiring, checking and complaining, our installers and retailers guide.