What Is A FENSA Certificate? Do You Need It?

Written by  John Davies
Last updated: October 23, 2023

A FENSA certificate is an official document for double-glazing replacement units on residential properties. It indicates that such units (windows, doors, or roofs) meet regulatory standards like safety, energy efficiency and warranty. It also proves that building control registered and approved the installation.

Therefore, if you want to install double-glazing replacement glass or sell a property with one, you need a FENSA certificate.

What is a FENSA certificate?

So, you already know that a FENSA certificate is a document issued for double-glazing replacement windows, doors and roofs. So, here are a few more details. FENSA stands for “Fenestration Self-Assessment Scheme”, and the English and Welsh governments added it to building regulations in April 2002.

To qualify for a FENSA certificate, the double-glazing replacement unit must be:

  • Compliant with building regulations
  • Made with energy-efficient (thermal insulated) materials
  • And registered with the local building control 

Therefore, a FENSA certificate essentially holds double-glazing installers and their customers, homeowners, to specified standards and regulations. That is why buyers and building inspectors ask for a FENSA certificate when looking at a building with double glazing. It is proof of compliance and quality. 

Do you need a FENSA certificate?

You need a FENSA certificate if:

  • The replacement double glazing was installed after April 2002
  • The building is a residential one
  • The original footprint of the building is untouched
  • If local building regulations require FENSA certificates

You don’t need a FENSA certificate if:

  • The double glazing is a fresh installation, not a replacement
  • If the project was just repairs instead of a complete replacement that includes frame and panes
  • The building is a commercial one
  • The building is listed
  • The installation isn’t part of the main building, i.e. a conservatory or extension.

How to get a FENSA certificate

You have two options.

  • Apply for the FENSA certificate yourself: Simply go to the building control department at your local council. You will have to pay for and schedule an inspection. The authorities will approve the certification after passing the inspection. You will probably get it in a couple of months.
  • Hire a FENSA-certified installer: Certified installers usually include this in their service. They will charge for it but the process will be faster (a month or less) and less stressful. This is one of the reasons you should use FENSA-certified installers for double glazing projects. 

Why you should hire a FENSA-certified installer

FENSA-certified installers charge more money than uncertified ones. However, they are the only ones that can guarantee the following. 

  • Compliance with regulations and standards: This is the point of the certification. It proves that the holder, the installer, can and will execute a project that meets industry standards and building regulations.
  • Competence and reliability: Installers can’t get or keep their certifications if they don’t have these two qualities.
  • Warranty and insurance: All FENSA-certified installers must have some form of protection for themselves, their employees and their clients.

How to find a FENSA-certified installer

You can use either the FENSA website or other resources.

  • The official Fensa website: They have a list of certified installers. Just enter your postcode to find certified installers in and around your area.
  • Other resources: This includes Google, local listings, recommendations etc. When you use these channels, confirm that the installer is FENSA-certified before hiring them.

What to do if you don’t have a FENSA certificate

The simplest solution is to get one. We have already discussed how. Sure, the certificate could take a while to arrive but waiting is easier than having trouble with buyers and the authorities.  

On the upside, it is easy to get a replacement if you misplace or damage the certificate. It only costs a visit to the FENSA website and a £25 fee.

However, if you want to do without a FENSA certificate, here are your options. 

  • Building Regulations certificate: You can use this too to prove compliance with building regulations and registration with building control.
  • Retrospective Building Regulation Compliance Certificate: As the name suggests, this is a certificate to get if you didn’t get building permission before installing the unit.
  • Double-glazing building regulations indemnity insurance: Only a buyer qualifies for this. You are not eligible if you are the one that installed the replacement double glazing. Plus, you can only get it if the installation is older than a year.


Essentially, a FENSA certificate is a document that holds installers and homeowners to a recommended standard for replacement double glazing. It proves an installation is up to standard and compliant with building regulations.

Therefore, as a homeowner, you must ensure that your double-glazing replacement units have FENSA certification. Even better, you should hire a FENSA-certified installer for such projects. Meanwhile, as a buyer, you should always ask for the FENSA certificates when looking at a property with replacement double glazing. 

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