Replacing windows and doors typically requires Building Regulations approval unless you use a FENSA-registered or CERTASS-registered installer who can self-certify the work, according to GOV.UK, 2026.
The answer depends on whether you do the work yourself or hire an installer. If a registered professional handles the replacement, they lodge compliance with Building Regulations on your behalf. If you DIY, you must apply for building control approval directly from your local authority before starting. The key variable is the glazing’s energy performance, replacement windows must achieve a minimum U-value of 1.6 W/m²K for windows and 1.8 W/m²K for doors, as set out in Approved Document L (GOV.UK, 2026).
Choose a FENSA or CERTASS registered installer
Using an installer registered with a Competent Person Scheme such as FENSA or CERTASS is the simplest route. These schemes allow the installer to self-certify that the work meets Building Regulations without you needing to notify the local authority. The Energy Saving Trust notes that replacing single glazing with double glazing can save around £195 per year on energy bills for a typical semi-detached home (Energy Saving Trust, 2026). The installer issues a certificate of compliance after completion, which you should keep for property records. If you later sell your home, buyers will ask for this certificate.
DIY replacement requires building control approval
If you replace windows or doors yourself, you must apply for building control approval from your local authority before starting work. The fee varies by council but typically ranges from £100 to £300 per application. You will need to demonstrate that the new glazing meets the required U-values and safety standards, toughened glass is mandatory for areas below 800mm from floor level, per Approved Document K (legislation.gov.uk, 2026). A building control officer will inspect the installation at key stages. Failure to get approval can lead to enforcement action and complications when selling the property.
Check grant eligibility for energy efficient replacements
The Great British Insulation Scheme offers support for some households, though it primarily targets insulation. For windows and doors, the Energy Company Obligation (ECO4) provides grants to low-income households for energy-efficient replacements, typically covering part of the cost. Ofgem states that ECO4 aims to improve the energy efficiency of homes with an EPC rating of D or below (Ofgem, 2026). Eligibility depends on your income, benefits, and property type. Contact your energy supplier or a certified installer to check if you qualify. Without grants, a standard double-glazed window replacement costs between £400 and £800 per window installed, according to industry averages.
A worked example
A typical 1930s semi-detached home in Manchester replacing all 10 windows and a back door with A-rated double glazing costs around £8,500 after the 0% VAT saving (in place until March 2027). The Energy Saving Trust estimates this saves roughly £195 per year on heating bills for a gas-heated home of this size. Over 25 years, the total saving reaches approximately £4,875, meaning the payback period sits at about 44 years when considering only energy savings. However, the real value comes from added comfort, reduced condensation, and a potential 5-10% uplift in property value, which can offset the upfront cost significantly. If the household qualifies for ECO4 funding or the Great British Insulation Scheme, the upfront cost could drop to zero for some or all of the work, dramatically improving the payback.
| Item | Figure |
|---|---|
| Upfront cost after grants | £8,500 |
| Yearly savings | £195 |
| Payback period | 44 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming any double glazing is compliant with Building Regulations, when in fact the glazing must meet a minimum U-value of 1.6 W/m²K for windows and 1.8 W/m²K for doors. Here are three frequent errors to avoid.
- Thinking FENSA registration is optional If you use an unregistered installer or DIY without approval, your local authority can demand you rip out the work and redo it at your own cost, which could exceed £10,000 in wasted materials and labour.
- Ignoring trickle vents for ventilation Modern airtight windows need controlled ventilation to prevent mould; omitting trickle vents can void your warranty and lead to damp problems that cost thousands to remediate.
- Believing the 0% VAT applies to all work The VAT reduction only covers labour and materials for the installation itself, not repairs or standalone supply-only purchases, so buying windows yourself and hiring a separate fitter could mean paying 20% VAT on the whole job.
Quick reference
- A FENSA or CERTASS registered installer can self-certify your window and door replacement under Building Regulations without you contacting the local authority.
- The minimum U-value for replacement windows in England is 1.6 W/m²K and for doors it is 1.8 W/m²K as set out in Approved Document L.
- ECO4 funding is available to low-income households and can cover the full cost of replacement windows and doors if your home has an EPC rating of D or below.
- Replacing single glazing with A-rated double glazing saves a typical semi-detached home around £195 per year on energy bills according to the Energy Saving Trust.
- DIY window replacement without prior building control approval can result in enforcement action and a legal requirement to redo the work at your own expense.
Frequently Asked Questions
Yes, unless you use a FENSA or CERTASS registered installer who self-certifies the work. If you DIY, you must apply for building control approval from your local authority before starting, as per GOV.UK 2026.
Replacement windows must achieve a minimum U-value of 1.6 W/m²K for windows and 1.8 W/m²K for doors, as set out in Approved Document L (GOV.UK 2026).
According to the Energy Saving Trust 2026, replacing single glazing with double glazing can save around £195 per year on energy bills for a typical semi-detached home.
