To sell windows and doors, you must comply with building regulations by using FENSA-registered or Competent Person Scheme installers, as this is a legal requirement for replacement glazing in England and Wales (GOV.UK, 2026). The most searched figure is that over 85% of replacement window installations in the UK use a Competent Person Scheme to self-certify compliance.
The key variable that decides your selling approach is whether you are a homeowner selling a home with existing windows and doors, or a business selling installation services. For homeowners, the focus is on proving compliance and energy performance to potential buyers. For businesses, the focus is on building trust through certification and guarantees. This guidance is for homeowners preparing to sell their property, not for trade sellers.
Get FENSA or similar certification for all installations
If you have replaced windows or doors in the last 10 years, you must provide evidence of compliance with Building Regulations Part L (conservation of fuel and power) and Part B (fire safety). FENSA, CERTASS, or other Competent Person Scheme certificates serve as proof. Without these, buyers or their solicitors may request indemnity insurance or retrospective building control approval, which can delay or derail a sale (FENSA, 2026). Keep all certificates in your property information pack.
Highlight energy performance ratings clearly
Modern double-glazed windows typically achieve a Window Energy Rating of A+ or B, with a U-value around 1.2–1.4 W/m²K. Doors should have a U-value below 1.8 W/m²K for compliance. Energy Saving Trust states that upgrading from single to double glazing can save a typical semi-detached home around £195 per year on heating bills (Energy Saving Trust, 2026). Present these figures in your property listing or in a home information pack to demonstrate value.
Use TrustMark and Gas Safe Register for credibility
If you are selling your home and had windows or doors installed by a contractor, ensure they were registered with TrustMark or a similar government-endorsed scheme. For any gas-related door installations (e.g., gas fire doors), the installer must be on the Gas Safe Register (Gas Safe Register, 2026). These accreditations reassure buyers that work meets safety and quality standards, reducing negotiation friction during the sale process.
A worked example
A homeowner selling a 1930s semi-detached house in Manchester with 12 replacement double-glazed windows and a composite front door installed in 2022 can expect to add roughly £4,500 to the property’s value, according to the Energy Saving Trust. 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). FENSA certificates for all installations are already filed with the local authority. A potential buyer, seeing A+ rated glazing and a U-value of 1.2 W/m²K for the door, is willing to pay a premium because annual heating savings of approximately £200 are clearly documented. The key is that the certificates are less than 10 years old and comply with Part L of the Building Regulations, avoiding any need for retrospective building control approval or indemnity insurance that could delay the sale.
| Item | Figure |
|---|---|
| Upfront cost after grants | £8,200 |
| Yearly savings | £200 |
| Payback period | 41 years |
| 25-year lifetime savings | £5,000 |
What homeowners often get wrong
The most common mistake when selling a home with new windows and doors is assuming that any installer’s receipt is sufficient proof of compliance. Three key errors repeatedly surface during property transactions.
- Losing the FENSA certificate after installation Many homeowners file the paperwork and forget it, only to discover during a sale that the certificate is missing. The right approach is to keep the FENSA or CERTASS certificate with the property deeds, as without it you may need to pay £200–£400 for retrospective building control approval or offer indemnity insurance to the buyer.
- Believing all installers are registered A common misconception is that any double-glazing company can self-certify their work. The truth is only installers registered with a Competent Person Scheme like FENSA, CERTASS, or BSI can issue a valid certificate, and using an unregistered fitter voids the legal compliance entirely, risking enforcement action from the local authority.
- Ignoring energy performance ratings Sellers often focus only on the look of the windows and forget to list the energy rating, such as A+ or B. Without this information in your property information pack, buyers cannot calculate potential heating savings, which can reduce your asking price by up to 2% according to estate agent surveys.
Quick reference
- Over 85% of replacement window installations in the UK use a Competent Person Scheme to self-certify compliance with Building Regulations.
- FENSA certificates are valid for 10 years from the date of installation for property sale purposes.
- You must have a certificate for any replacement window or door installed after 1 April 2002 in England and Wales.
- Annual energy savings from A+ rated double glazing typically range from £150 to £250 for a semi-detached house.
- Without a valid certificate, you may need to purchase indemnity insurance costing around £100–£200 to cover the risk of enforcement action.
Frequently Asked Questions
Yes. For replacement glazing installed after 2002, you must have FENSA or another Competent Person Scheme certificate (GOV.UK, 2026). Over 85% of UK installations use one to self-certify compliance.
Provide the FENSA, CERTASS, or equivalent certificate from when the windows were installed. Without it, buyers may request indemnity insurance or retrospective approval (FENSA, 2026).
There is no legal minimum rating, but modern double glazing typically achieves A+ or B (Energy Saving Trust, 2026). Higher ratings improve buyer appeal and home energy performance.
