Yes, windows and doors are typically covered under the same building regulations approval when they form part of a building’s thermal envelope, but the specific rules differ for replacement work versus new installations. According to Approved Document L of the Building Regulations (2026 edition), both must meet minimum U-value standards to control heat loss.
The answer depends on whether you are replacing existing windows and doors or installing them in a new extension. For replacements, you can use a FENSA-registered installer to self-certify compliance, or apply for building regulations approval separately. For new-build or extension work, windows and doors must always be included in the full plans submission. The rules apply to all residential buildings in England and Wales, though Scotland has its own standards under Section 6 of the Building Standards.
U-value standards for windows and doors
Building regulations require new windows to achieve a whole-window U-value of no more than 1.4 W/m²K, while doors must achieve a U-value of 1.4 W/m²K for half-glazed doors or 1.0 W/m²K for fully opaque doors (Approved Document L, 2026). These values apply to both timber and uPVC frames. If you install a window or door that fails to meet these standards, you risk enforcement action from your local authority building control department.
FENSA certification and self-certification
Replacement windows and doors in existing dwellings can be installed by a FENSA-registered installer, who will self-certify that the work meets building regulations. FENSA-registered installers must provide a certificate of compliance within 28 days of installation (FENSA, 2026). Without this certificate, you may face difficulties when selling your home, as buyers’ solicitors typically request evidence of compliance. If you use a non-registered installer, you must apply for building regulations approval from your local council before work starts.
Cost implications and VAT treatment
The average cost of replacing windows and doors in a three-bedroom semi-detached house ranges from £4,500 to £7,500, depending on materials and glazing type (Energy Saving Trust, 2026). 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 Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing.
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 same household could save around £450 per year on energy bills according to the Energy Saving Trust, because heat loss through old windows and doors accounts for up to 20% of a typical home’s total heat loss. If you are eligible for ECO4 funding, which depends on receiving certain benefits and having an EPC rating of E, F or G, your upfront cost could drop to near zero. Without ECO4, the payback period on a £12,000 investment is roughly 27 years at current energy prices, which makes windows and doors a lower priority than loft insulation or an air source heat pump for most households.
| Item | Figure |
|---|---|
| Upfront cost after grants | £12,000 |
| Yearly savings | £450 |
| Payback period | 27 years |
| 25-year lifetime savings | £11,250 |
What homeowners often get wrong
The most common mistake is assuming all double glazing meets the current Building Regulations U-value standard of 1.4 W/m²K for windows. Here are three specific errors that cost homeowners money and cause compliance headaches.
- Relying on an installer without FENSA registration Many homeowners assume any double-glazing company can self-certify compliance under Building Regulations. If your installer is not FENSA or CERTASS registered, you must apply separately to your local building control office, a process that costs £300 to £600 and can delay your project by weeks.
- Ignoring door U-value differences People often buy a fully glazed door thinking it meets the same standard as a window. A half-glazed door must achieve 1.4 W/m²K, but a fully opaque door must hit 1.0 W/m²K. Installing a door that misses this target means it fails Building Regulations, and you may be forced to replace it before selling your home.
- Thinking trickle vents are optional Many homeowners remove or block up trickle vents on replacement windows to reduce draughts. Under Part F of the Building Regulations, replacement windows must include adequate background ventilation. Removing vents without adding alternative ventilation can void your FENSA certificate and create condensation problems that lead to mould.
Quick reference
- New windows must achieve a whole-window U-value of no more than 1.4 W/m²K under Approved Document L 2026.
- Fully opaque doors must achieve a U-value of 1.0 W/m²K, while half-glazed doors can meet 1.4 W/m²K.
- Replacement windows and doors installed by a FENSA-registered installer do not require separate Building Regulations approval.
- The Energy Saving Trust estimates that draught-proofing windows and doors costs £50 to £200 and can save £50 per year on energy bills.
- Fitting windows and doors without Building Regulations approval can lead to enforcement action and difficulty selling your home under the Propertymark questionnaire.
Frequently Asked Questions
Yes, both need approval when part of the thermal envelope. According to Approved Document L 2026, replacements can be self-certified by a FENSA installer, but new builds always require plans submission.
New windows need a whole-window U-value of no more than 1.4 W/m²K. Doors require 1.4 W/m²K for half-glazed and 1.0 W/m²K for fully opaque types, per Approved Document L 2026.
Not unless you use a FENSA-registered installer who self-certifies compliance. Otherwise, you must apply to your local authority building control, or risk enforcement action.
