FENSA and self-certification: how supply-only windows get signed off
Replacement windows must be certified as Building Regulations-compliant, and there are exactly two routes: a competent-person-scheme installer self-certifies the job, or you notify building control and they inspect it. Buying supply-only doesn't change the rules — it just means the route is your choice rather than bundled into an installer's price.
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 spec: U-value 1.4 or better / WER band B or better — our standard spec, shown on your order confirmation
- 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
- Fire egress: a compliant escape opener in bedrooms above ground floor
- Workmanship: fixing, packing, sealing and operation of the installed windows
The paperwork, and why it matters later
Keep your order confirmation (it documents the specification), plus the FENSA/Certass certificate or building-control completion certificate. 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 (glazing, ratings), which your order confirmation documents.