The windows and doors industry falls under the fenestration sector, which covers the design, manufacture, installation and maintenance of glazed products. In 2026, this industry employs over 200,000 people in the UK and generates annual revenue exceeding £8 billion (GOV.UK, 2026).
Fenestration is a specialised branch of the broader construction and building products industry. It includes everything from uPVC, aluminium and timber frames to double and triple glazing, doors, conservatories and curtain walling. The sector is regulated by building standards such as Part L (conservation of fuel and power) and requires certified installers via schemes like FENSA or CERTASS for compliance.
Fenestration is the formal industry name
The term fenestration comes from the Latin fenestra, meaning window. It is the recognised technical name for the windows and doors industry in UK building regulations and trade bodies. The Glass and Glazing Federation (GGF) represents the sector, which covers residential and commercial installations. In 2026, over 90% of new-build homes in England use double or triple glazing sourced from fenestration manufacturers (BRE, 2026).
Building regulations define the industry scope
Approved Document L of the Building Regulations sets minimum energy performance standards for windows and doors. For replacement installations, a U-value of 1.6 W/m²K or lower is required for windows, and 1.8 W/m²K for doors. Industry bodies like FENSA and CERTASS register installers and certify compliance. Without proper certification, homeowners cannot legally sell their property without a Building Regulations Compliance Certificate (GOV.UK, 2026).
Installation falls under construction trades
Window and door fitters are classified under Standard Industrial Classification (SIC) code 43.32 – Joinery installation. This places the industry firmly within the construction sector, specifically specialised construction activities. The industry is distinct from general building work because it requires specific skills in measuring, sealing and glazing. The average cost for a standard uPVC window installation in 2026 is £400–£600 per unit, including labour and materials (TrustMark, 2026).
A worked example
Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). The Energy Saving Trust estimates annual heating savings of £195 for a gas-heated home like this, cutting 330 kg of CO₂ per year. With a payback period of roughly 33 years, the financial case relies on improved comfort, reduced condensation and added property value rather than quick cost recovery. Over 25 years, total savings reach £4,875, not accounting for rising energy prices. If the householder qualifies for the ECO4 scheme, partial funding may reduce upfront costs further. All installations must meet Part L building regulations, requiring a U-value of 1.6 W/m²K or lower, and must be certified by a FENSA or CERTASS registered installer to comply with building regulations.
| Item | Figure |
|---|---|
| Upfront cost after grants | £6,500 |
| Yearly savings | £195 |
| Payback period | 33 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming all double glazing is the same, leading to poor energy performance and wasted money. Here are three frequent errors homeowners make when choosing windows and doors.
- Choosing the cheapest quote without checking U-values Many homeowners pick the lowest price, unaware that a window with a U-value of 1.8 W/m²K loses more heat than one rated 1.2 W/m²K. Paying £500 more for better glazing can save £80 per year on heating bills and meet Part L standards properly.
- Assuming all installers are equally qualified Some firms offer lower prices by skipping FENSA or CERTASS registration. Using an unregistered installer voids building regulation compliance and can cost £1,000 or more to fix later when selling the home, as solicitors demand certification.
- Ignoring the door material impact on insulation Many choose a composite door for style but overlook its thermal performance. A poorly insulated composite door with a U-value above 1.8 W/m²K can undo savings from new windows, adding £50 to annual heating costs compared to a well-rated model.
Quick reference
- The fenestration industry employs over 200,000 people in the UK and generates £8 billion in annual revenue.
- Part L building regulations require new windows to achieve a U-value of 1.6 W/m²K or lower from 2025 onwards.
- Over 90% of new-build homes in England use double or triple glazing from fenestration manufacturers.
- Replacing single glazing with A-rated double glazing saves a typical semi-detached home £195 per year on heating.
- Installation must be certified by FENSA or CERTASS to comply with building regulations and avoid legal issues when selling.
Frequently Asked Questions
The fenestration industry covers the design, manufacture, installation and maintenance of windows, doors, glazing and related products. According to GOV.UK, it is a specialised branch of the construction sector.
Approved Document Part L sets minimum energy standards: windows must have a U-value of 1.6 W/m²K or lower. FENSA and CERTASS are the main installer certification schemes recognised by building control.
The fenestration sector employs over 200,000 people in the UK as of 2026. This includes roles in manufacturing, installation, design and maintenance across residential and commercial projects.
