Do I need FENSA if I fit my own windows? How sign-off works

Route 1: a registered installer fits your windows

FENSA and Certass are the main competent-person schemes for window installation in England and Wales. An installer registered with one can fit windows you supply and self-certify the work. They notify the scheme, and a certificate is issued to the property. Before booking, confirm two things: that they're currently registered (both schemes have online checkers), and that they're willing to certify customer-supplied windows, since certifying means vouching for the whole installation including the specification.

Route 2: building control (DIY or unregistered fitter)

If you fit the windows yourself or use a fitter who isn't scheme-registered, submit a building-notice or full-plans application to your local authority building control (or an approved inspector) before starting. An inspector checks the work (typically the glazing spec, safety glass locations, ventilation and egress) and issues a completion certificate. There's an application fee, set by each authority.

What the certifier will look at

• Thermal performance: a U-value of 1.4 W/m²K or better, or WER band B or better. Our energy ratings guide sets out our standard specification, and your order page lists the glazing chosen for each item
• Safety glass in critical locations: below 800mm, beside doors. Order toughened or laminated there
• Background ventilation: trickle vents at least matching what was removed, and expected in habitable rooms
• Means of escape: an escape window wherever Approved Document B asks for one. Our Building Regulations guide explains which rooms
• Workmanship: fixing, packing, sealing and operation of the installed windows

The paperwork, and why it matters later

Keep a record of what was fitted: save or print your order page, which lists the glazing and options on every item, and keep your invoice. The standard specification behind them is in our energy ratings guide. Keep the FENSA or Certass certificate, or the building-control completion certificate, with them. When you sell, your buyer's solicitor will ask for evidence that any window replacement was certified. Having it saves you an indemnity policy or a retrospective application years later.

Frequently asked questions

Will a FENSA installer fit windows I bought myself?

Many will. Supply-only fitting is routine work for independent installers. Ask up front and confirm they'll register the job with their scheme; that certificate is half of what you're paying them for.

Can I self-certify as a DIYer?

No, self-certification is only available to scheme-registered businesses. DIY installations use the building-control route.

How much does building control cost for windows?

Fees are set by each local authority and vary; check your council's building-control fee schedule for 'replacement windows/controlled fittings'. We don't quote figures because they genuinely differ across councils.

Is FENSA a quality mark on the windows themselves?

No, FENSA certifies installations, not products. The windows' own compliance comes from their specification. Your order page lists the glazing and options on each item, and our energy ratings guide explains the standard specification.

Sources

The official documents and schemes this page refers to. Rules change, so check the current version, and ask your fitter or building control if you're not sure.

• FENSA: competent person scheme for windows and doors
• Certass: competent person scheme for windows and doors
• Approved Document L: Conservation of fuel and power: U-values and energy ratings
• Approved Document K: Protection from falling, collision and impact: safety glass and guarding
• Approved Document F: Ventilation: background ventilation and trickle vents
• Approved Document B: Fire safety (volume 1 covers dwellings): escape windows