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FENSA, Building Regulations and Supply-Only Windows: What You Actually Need to Know

You can buy and fit your own windows. Here is what the regulations actually require.

If you have been looking at supply-only windows and wondering whether you can legally fit them yourself, the short answer is YES - you can. What you cannot do is skip the compliance step.

Know the Rules | Order Direct | Stay Compliant

What UK Building Regulations Mean for Supply-Only Window Buyers.

FENSA, building regulations, building control and self-certification; these terms get used interchangeably by salespeople, forum posters, and well-meaning neighbours. Most of the time, they are not used accurately. Window Supply Direct supplies made-to-measure uPVC windows and doors on a supply-only basis directly to homeowners across England and Wales, so we see the confusion first-hand. Every unit we supply is built to meet the latest UK building regulations out of the box. Here is what the compliance landscape actually looks like.

What is FENSA and what does it actually do?

FENSA stands for the Fenestration Self-Assessment Scheme. It was set up in 2002 to allow registered window installers to self-certify their own work against building regulations, without the homeowner needing to involve their local council or building inspector each time.

When a FENSA-registered company installs your windows, they sign off the job themselves and register it with FENSA. You receive a certificate, usually within 30 days, confirming that the installation meets building regulations. That certificate is what your solicitor will ask for if you ever sell the property.

FENSA is not a quality mark. It is not a guarantee that the installation was done well, that the product is premium, or that the price was fair. It is a paper trail confirming compliance.

fensa house

Does fitting your own windows mean you cannot get FENSA certification?

Correct. FENSA certification is only available through registered installers. If you buy supply-only windows from Window Supply Direct and install them yourself or use a local fitter who is not a FENSA approved installer you cannot receive a FENSA certificate.

That does not mean your installation cannot be compliant or certified. It means you use the alternative route: Local Authority Building Control.

The Two Routes to Compliance

Route 1

FENSA-registered installer

Route 2

Local authority building control

FENSA-registered installer fits the windows
You self-install, or use a non-registered local fitter
Installer self-certifies the work
You notify your Local Authority Building Control before work starts
FENSA certificate issued to you within 30 days
Building control inspector visits to check the installation
No council involvement required
Council issues a completion certificate once satisfied the install meets building regulations
Slightly higher installation cost
Inspection fee typically £100–£200 depending on location

How the building control route works, step by step

Contact your local authority before you start work. Most councils have an online portal for building control applications. You are notifying them of your intention, not asking for permission.

What do building regulations actually require from replacement windows?

The requirements sit across several parts of the regulations. For most like-for-like window replacements in a standard UK home, they come down to four things:

THERMAL PERFORMANCE — Part L

VENTILATION — Part F

FIRE ESCAPE — Part B

SAFETY GLAZING — Part K

How Much Do New uPVC Windows Cost in the UK - Blog2

Common misconceptions, answered plainly

DIY window installation is illegal in the UK

Without FENSA I cannot sell my house

Building control takes months and costs a fortune

FENSA certification guarantees good quality windows

You can only buy windows through a double glazing company

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