FENSA Registration Calculator — Window & Door Compliance

FENSA (Fenestration Self-Assessment Scheme) is a government-authorised competent person scheme for replacement windows and doors in England and Wales. FENSA-registered installers can self-certify that their work complies with Building Regulations (Part L thermal performance, Part K safety glazing/impact, Part F ventilation/trickle vents) without needing a separate building control application. Note: Part N was withdrawn and merged into AD K in 2013.

All replacement windows and external doors must comply with Building Regulations. You either need: a FENSA (or CERTASS) registered installer who self-certifies compliance, OR a building control application with your local authority (at additional cost). Without either, the work is uncertified and will cause problems when selling.

FENSA annual membership is typically £400–£600 depending on company size, plus a per-installation notification fee of approximately £30–£40 per installation. The total annual cost depends on the volume of jobs. For a typical installer doing 40+ jobs/year, FENSA is significantly cheaper than building control.

The alternative is a building control application for each installation, typically costing £200–£400 per job. Building control will inspect the windows for thermal compliance (Part L U-values: 1.4 W/m²K windows / 1.4 doors per AD L 2021 Table 4.2), safety glazing (AD K critical locations ≤1500mm) and ventilation (Part F trickle vents). This is more expensive for multiple installations but may suit very occasional work.

Uncertified window replacement is a Building Regulations offence. When selling the property, the solicitor will request FENSA certificates or building control completion certificates. Without them, the seller may need to apply for retrospective building control regularisation (costing £200–£400+) or the buyer may reduce their offer.