Do Timber Windows Need a FENSA Certificate? Understanding Your Options

If you’re replacing timber windows or external doors, you may have come across the term “FENSA certificate” and wondered whether it applies to your project.

It’s one of the most common questions homeowners ask when replacing windows — particularly in older properties, listed buildings and period homes where timber windows are often the most suitable option.

The short answer?

In many cases, replacement windows and doors do need to comply with Building Regulations — but a FENSA certificate is not the only way this can be handled.

At GS Haydon & Son Ltd, we manufacture and install bespoke timber windows and doors across North Devon. We’re also registered with Certass, which means we can self-certify qualifying installations and provide the relevant compliance documentation as part of our service.

What is a FENSA certificate?

FENSA is one of the best-known certification schemes for replacement windows and doors in England and Wales.

Installers registered with FENSA can certify that replacement windows and doors meet current Building Regulations without the homeowner needing to apply separately through local authority Building Control.

Because the name is so well known, many people use the phrase “FENSA certificate” as a catch-all term — even though it’s only one route.

Certass is another approved route

This is where many homeowners get confused.

Certass is another government-authorised competent person scheme that allows registered installers to self-certify replacement windows and doors.

That means if your installation qualifies, you do not specifically need a FENSA certificate.

What you need is proof that your installation complies with Building Regulations.

At GS Haydon & Son Ltd, we’re Certass registered, so we can manage this as part of your project.

When do replacement timber windows need certification?

In many cases, Building Regulations approval applies when you are:

Replacing existing windows entirely
Installing new external doors
Upgrading glazing
Changing thermal performance of existing openings

This often applies whether you’re installing timber, aluminium or uPVC products.

What about repairs?

If you’re repairing existing windows rather than replacing them entirely, certification may not be required.

Examples may include:

Repairing rotten timber sections
Replacing cords in sash windows
Draught proofing existing windows
Refurbishing historic joinery

This can vary depending on the scope of work, so it’s always worth discussing your specific project.

Listed buildings and conservation areas

This is particularly relevant in North Devon, where many homeowners live in older or period properties.

If your property is listed or located within a conservation area, there may be additional planning considerations alongside Building Regulations requirements.

You may need approval from your local authority before replacing windows.

For North Devon homeowners, that may involve North Devon Council or Exmoor National Park Authority depending on your location.