Window installations in 2025: A homeowner's guide to regulations and peace of mind

New windows are a fabulous upgrade to modernise your home whilst improving energy efficiency and improving security.

But what many homeowners don’t realise is that replacing your windows isn’t just a matter of picking a stylish frame and glass. It’s also about complying with UK building regulations - and protecting yourself from costly mistakes or legal headaches down the line.

In 2025, legislation and standards around windows have never been more rigorous. That’s why working with an accredited, vetted installer is crucial if you’re planning to invest in your home.

Let’s unpack what you need to know.

Why legislation and regulations matter

In the UK, installing new windows isn’t a minor job - it’s considered a “controlled fitting.” That means it falls under Building Regulations, which are legal requirements designed to ensure homes are safe, energy-efficient, and secure.

Some of the key regulations affecting window installations include:

• Thermal Performance (Approved Document L)
  New window installations need to meet the minimum standards for heat retention to help the UK meet its carbon reduction targets. In 2025, these regulations have tightened, demanding better U-values (the measure of heat loss through the window) than ever before.
  
  

• Safety Glazing (Approved Document K & N)
  Certain windows - particularly those near floor level, in doors, or in bathrooms - need to use safety glazing to prevent serious injuries if broken.
  
  

• Ventilation (Approved Document F)
  Replacing old windows can unintentionally reduce ventilation in your home. New regulations state that adequate airflow is required to avoid damp and mould, which can harm your health.
  
  

• Structural Integrity
  Installers should ensure that windows are fitted without compromising your property’s structural stability or weatherproofing.
  
  

If your installation doesn’t comply, local authorities can require you to correct the work at your own cost. Plus, non-compliant work can cause problems when you come to sell your home, as missing paperwork or certificates may halt your sale.

Competent person schemes

Navigating building regulations yourself can be daunting. That’s why the UK government recognises Competent Person Schemes. These are official schemes that enable accredited installers to self-certify their work as compliant with Building Regulations, saving homeowners time, hassle, and fees.

Two of the most prominent schemes in the window and door industry are:

FENSA

FENSA (Fenestration Self-Assessment Scheme) was established in 2002 and is the best-known name in the industry. FENSA-approved installers can:

• Self-certify window and door installations under Building Regulations.

• Provide you with a FENSA certificate (often requested during property sales).

• Offer an insurance-backed guarantee, giving you peace of mind should something go wrong.

CERTASS

CERTASS is another government-authorised scheme offering similar benefits:

• Competent installers who comply with regulations.

• A certificate of compliance for your records and future home sales.

• Access to Insurance-backed guarantees for financial protection.

Both FENSA and CERTASS hold their members to high standards, performing regular audits to ensure ongoing competence and quality workmanship.

Energy Efficiency and Sustainability

With energy costs high and sustainability at the forefront, we can’t talk about modern window replacements without addressing energy efficiency. Windows play a massive role in reducing your home’s carbon footprint and running costs.

New regulations introduced in 2022 and further updated in 2025 have pushed for even lower U-values, meaning modern double and triple glazing now offers excellent thermal performance. This can translate into lower heating bills and a more comfortable living environment year-round.

Accredited installers are trained on the latest products and technologies, helping you choose windows that not only comply with regulations but also maximise efficiency and comfort.

Choosing your window installer

• Ask if your installer is registered with FENSA, CERTASS, or another competent person scheme.

• Request to see proof of membership.

• Ensure you’ll receive a certificate of compliance once the job is complete.

• Confirm whether you can access an insurance-backed guarantee.

At The CPA, we champion vetted, accredited professionals who put homeowners first. Investing in your home should be exciting, not stressful. By working with trusted experts, you can improve your property safely, legally, and with full confidence.