FENSA, CERTASS & GGF explained
When you compare double glazing companies, accreditation is one of the quickest ways to separate a properly run firm from a chancer. The badges you will see most often are FENSA, CERTASS and the GGF — and they do not all mean the same thing. This guide explains what each one covers, why it matters for Building Regulations, and how to verify it before you choose.
Why accreditation matters
Replacement windows and doors in England and Wales must meet Building Regulations, chiefly for thermal performance, safety glazing and ventilation. There are two ways to prove compliance: use an installer registered with a competent person scheme who can self-certify the work, or make a separate building control application yourself. The first route is simpler, faster and usually cheaper — which is why FENSA and CERTASS registration is worth confirming on any quote.
FENSA and CERTASS
FENSA and CERTASS are both government-authorised competent person schemes. A firm registered with either can certify that your replacement glazing meets Building Regulations and register the work, so you receive a certificate that matters when you come to sell or remortgage. They do the same essential job, so a firm registered with one does not need the other. If a company cannot confirm registration with either, treat that as a reason to slow down. Our guide to double glazing quote red flags covers other warning signs to keep in mind.
The Glass and Glazing Federation (GGF)
The GGF is a trade association rather than a certification scheme. Membership is not proof of Building Regulations compliance, but it does show a firm has signed up to an industry code of practice and gives you an additional avenue for support if a dispute arises. Think of it as a helpful extra rather than a substitute for FENSA or CERTASS.
Comparing accredited installers? We match you with vetted double glazing firms so you can check credentials and quotes side by side — free and with no obligation.
Reputation sits alongside accreditation
Accreditation proves competence on paper; reputation tells you how a firm actually behaves. Read independent reviews as well as checking scheme registration. For example, our installation partner Help 2 Buy Windows — rated No.1 for double glazing on Trustpilot pairs the right credentials with a strong body of verified feedback, which is the combination worth looking for. It is also sensible to read how to vet an installer first and to walk through the quote process step by step so you know what good looks like.
How to verify a firm's credentials
Ask for the registration number and confirm it on the relevant scheme's own website, rather than trusting a logo on a van or a brochure. Cross-check the company name and address at the same time. If you are still deciding on products, it helps to compare glazing types before you compare firms and to review materials ranked and reviewed, so accreditation is one of several boxes you tick rather than the only one.
Accreditation questions, answered
What is FENSA?
FENSA is a government-authorised competent person scheme for replacement windows and doors. A FENSA-registered installer can self-certify that the work meets Building Regulations and register it, so you receive a certificate without needing separate approval from building control.
What is CERTASS?
CERTASS is another competent person scheme that does the same job as FENSA. A CERTASS-registered firm can self-certify replacement glazing against Building Regulations and issue a certificate. Either scheme is acceptable, so a firm registered with one does not also need the other.
What is the GGF?
The Glass and Glazing Federation is a trade association for the glazing industry. Membership is not a competent person scheme, but it signals that a firm follows the GGF’s code of practice and gives you an extra route for support if a dispute arises.
Do I legally need FENSA or CERTASS?
Replacement windows and doors must comply with Building Regulations. Using a FENSA or CERTASS-registered installer is the simplest way to prove compliance, because they self-certify and register the work. Otherwise you would need to arrange a building control application yourself, which is slower and usually more expensive.
How do I check a firm’s accreditation?
Ask for the firm’s registration number and confirm it on the relevant scheme’s website, rather than relying on a logo on a van or a brochure. A genuine installer will be happy to provide it, and you can cross-check it in a couple of minutes before you commit.