FENSA vs CERTASS: Which Scheme for Window Installers?

If you install replacement windows, doors, or roof windows in England and Wales, you need to comply with Part L of the Building Regulations — the energy efficiency requirements. The practical way to do this is joining a competent person scheme that lets you self-certify your installations.

The two main schemes are FENSA and CERTASS. Both are government-authorised. Both let you self-certify. But they differ in cost, reputation, assessment process, and what else they offer.

This guide breaks down the differences so you can make the right choice for your glazing business.

Why you need a scheme

Part L of the Building Regulations requires that replacement windows, doors, and roof windows meet minimum thermal performance standards (U-values). When you install them, the work must be certified as compliant.

You have two options:

1. Join a competent person scheme (FENSA or CERTASS) and self-certify every installation
2. Apply to Building Control for each job — costing the homeowner £200-400 and adding weeks of delay

Option 1 is what customers expect. Without it, you're asking them to pay extra and wait longer. Most will hire someone who's registered.

Scotland and Northern Ireland have different arrangements. Scotland uses CERTAS (not the same as CERTASS) under the Building (Scotland) Regulations. Northern Ireland uses FENSA and CERTASS under their own competent person scheme framework.

FENSA: the overview

The Fenestration Self-Assessment Scheme. Established in 2002, run by the Glass and Glazing Federation (GGF). The older, larger, and more widely recognised scheme.

What you get

• Self-certification for replacement windows, doors, and roof windows
• Listed on the FENSA website (consumer search tool with ~2 million certificates issued)
• Automatic notification to Building Control and energy assessors
• Use of the FENSA logo — strong consumer recognition
• Access to FENSA technical guidance and helpline
• Insurance-backed guarantee scheme for consumers
• GGF membership benefits (optional add-on)

Cost

Total annual cost for a typical glazing firm doing 200 installations/year: roughly £1,500-3,000 including per-cert fees.

Assessment

FENSA requires a pre-registration desktop assessment, followed by on-site inspection of your work. Ongoing: annual re-assessment and random installation inspections.

Reputation

FENSA has strong consumer recognition. When homeowners search "check if my installer is registered," they usually search FENSA first. Estate agents and solicitors recognise FENSA certificates for property transactions. This matters — buyers need proof of compliant installations when selling a house.

CERTASS: the overview

Competent person scheme for glazing, launched in 2006. Smaller than FENSA but growing. Independently run (not tied to the GGF).

What you get

• Self-certification for replacement windows, doors, and roof windows
• Listed on the CERTASS consumer search tool
• Automatic Building Control and EPC notification
• Use of the CERTASS logo
• Technical support and helpline
• Insurance-backed guarantee scheme
• Access to CERTASS training resources

Cost

Total annual cost for a typical firm doing 200 installations/year: roughly £1,200-2,500 including per-cert fees. Generally cheaper than FENSA.

Assessment

Similar to FENSA: pre-registration assessment, on-site inspection, ongoing random checks. Some installers report CERTASS assessments being slightly more practical and less bureaucratic.

Reputation

CERTASS has grown significantly since 2006 but is still less recognised than FENSA among consumers. Solicitors and estate agents accept CERTASS certificates — they're legally equivalent to FENSA. But some homeowners specifically ask for "FENSA-registered" installers, not knowing CERTASS exists.

Head-to-head comparison

Which should you choose?

Choose FENSA if:

• Consumer recognition matters to your sales. If you compete for domestic work where homeowners are comparing installers, the FENSA name carries weight. Many consumers specifically search for "FENSA-registered" when choosing a window company.
• You want GGF membership benefits. FENSA registration can be bundled with GGF membership, which offers additional industry representation, legal advice, and commercial benefits.
• You work with estate agents or new-build developers. FENSA's larger database and longer track record means it's the first scheme many property professionals check.

Choose CERTASS if:

• Cost is a priority. CERTASS is typically 10-20% cheaper than FENSA across registration, annual fees, and per-certificate costs. For a firm doing 300+ installations/year, that saving adds up.
• You value independence. CERTASS isn't tied to a specific trade association. Some installers prefer this neutrality.
• Your customers don't specify. If most of your work comes through recommendations, trade reputation, or commercial contracts rather than consumer search tools, the scheme brand matters less.

Can you join both?

Technically yes, but there's no practical reason to. Both schemes do the same legal job — self-certification of Building Regulations compliance. Paying for two schemes doubles your cost without doubling your benefit. Pick one.

Common misconceptions

"FENSA certificates are worth more than CERTASS"

False. Both are equally valid under the Building Regulations. A CERTASS certificate has identical legal standing to a FENSA certificate. Solicitors must accept both.

"You need FENSA to install windows legally"

False. You need a competent person scheme OR Building Control sign-off. CERTASS is equally valid. And for repair work or like-for-like replacements that don't change the thermal element, you may not need either.

"CERTASS is new and unproven"

It launched in 2006 — that's 20 years of operation. It's government-authorised and regularly audited by the Department for Levelling Up, Housing and Communities.

"The assessment is harder with one than the other"

Both schemes follow similar assessment frameworks. The practical experience varies by assessor rather than scheme.

What about Scotland?

Scotland operates under different building regulations. The main competent person scheme for glazing in Scotland is CERTAS (Construction, Engineering, Regulatory, Technical Assessment Scheme) — confusingly similar in name to CERTASS but a separate scheme.

If you operate across England/Wales and Scotland, you may need registration with both your chosen English/Welsh scheme and the Scottish equivalent.

Tracking scheme compliance in your business

Whichever scheme you join, you need to:

• Track every installation — date, address, certificate number, window specifications
• Submit notifications — your scheme needs details of every job for Building Control
• Keep records — at least 15 years (the limitation period for Building Regulations work)
• Monitor assessment dates — don't let your registration lapse
• Track installer qualifications — which of your fitters are covered under your registration

Job management software that links every installation to a compliance record — with the certificate reference, U-values achieved, and notification status — makes this automatic rather than admin-heavy.

Muster tracks scheme certifications with automatic expiry alerts, links compliance records to every job, and keeps a searchable archive that's ready for any assessment visit. Combined with quoting, scheduling, invoicing, and Muster Pay for collecting payment at completion, it covers the full glazing business workflow.

See how it works.