Building regulations 2026: What Part L changes mean for replacement windows
- 28 November 2025
- News
Building regulations 2026: what Part L changes mean for replacement windows
As we approach 2026, the landscape of UK building regulations is shifting significantly. The latest updates to Part L of the Building Regulations mark a major step towards reducing carbon emissions, improving energy efficiency, and futureproofing homes. For homeowners planning renovations or replacement windows, understanding these changes is crucial. Choosing compliant products not only ensures peace of mind but also protects against costly delays from local authority building control checks.
From U-values and Window Energy Ratings to installer certifications and documentation, the 2026 regulations raise the bar for new and existing residential buildings. At Crown Conservatories, Windows and Doors Ltd, we help homeowners navigate these updates, ensuring every window we install meets or exceeds the new standards.
Current Part L U-values and building regulations as we enter 2026
Part L of the Building Regulations is all about the conservation of fuel and power, minimising a home’s dependence on fossil fuels. It sets minimum standards for energy performance, insulation, heating, ventilation, and glazing. The updates ahead of 2026 tighten requirements for thermal efficiency across all building elements, including walls, roofs, floors, windows, and doors.
Understanding U-values
U-values measure how effectively a building element resists heat loss. The lower the U-value, the better the thermal performance. Part L changes mean windows and doors must now meet stricter thermal standards, helping homeowners reduce energy bills and their carbon footprint.
Comparison of U-values – 2021 vs 2025/2026:
| Building element | 2021 U-value (W/m²K) | 2025/2026 U-value (W/m²K) |
| Walls | 0.26 | 0.18 |
| Roof | 0.16 | 0.11 |
| Floor | 0.18 | 0.13 |
| Windows | 1.6 | 1.2 |
| Doors | 1.8 | 1.4 |
Meeting these targets is essential for Part L compliance and contributes to less carbon emissions in your home. Local authorities will require verification through SAP calculations, photographic evidence, and airtightness testing, so planning ahead is key.
Why Part L matters for homeowners
- Reduces heat loss, keeping homes warmer in winter and cooler in summer
- Lowers energy bills by improving efficiency
- Helps achieve sustainability goals and supports the UK’s net-zero targets
- Ensures compliance with local authority building control, avoiding costly delays
Energy efficient windows that exceed 2026 standards
At Crown Conservatories, Windows and Doors Ltd, we offer a wide range of energy-efficient replacement windows designed to meet current and future standards. Our windows are thermally efficient, durable, and stylish, making them a smart choice for any home renovation project.
Window styles
We provide a bespoke selection of window types to suit every home style:
- Casement windows – hinged at the side, opening outward; versatile and classic
- Flush sash windows – sleek and level with the frame; ideal for contemporary or heritage properties
- Sliding sash windows – traditional vertical sliding design; perfect for period homes
- Tilt and turn windows – dual functionality; tilt for ventilation, turn for full opening
- Georgian windows – decorative grids mimic historic designs; combine style and energy efficiency
- Lead windows – incorporate leaded glazing patterns; perfect for character properties
Sliding sash windows excel when it comes to allowing ventilation into your home.
Window materials
Our windows are available in durable, low-maintenance materials:
- uPVC – highly energy-efficient, weather-resistant, and affordable
- Aluminium – strong, slimline frames for a contemporary look
- Timber-effect uPVC – combines traditional wood look with modern low-maintenance benefits
Each window is made to measure, allowing for a perfect fit, colour customisation, and glazing choices such as double glazing, triple glazing, or acoustic glass for quieter interiors.
Frequently asked questions
What do the 2026 Part L changes mean for my replacement windows?
Your windows must now meet lower U-values, contribute to overall energy efficiency, and be installed by a FENSA-registered or competent person scheme installer. Choosing compliant products ensures peace of mind and prevents issues with local authority building control.
Are renovations and extensions affected?
Yes, all renovations, extensions, and replacement windows must meet current Part L standards, including insulation, glazing, and ventilation requirements.
Who are Crown?
Crown Conservatories, Windows and Doors Ltd is a family-run company with over 20 years of experience. Based in Milton Keynes, we serve homeowners across Buckinghamshire, Bedfordshire, and Northamptonshire. Our services include:
- Made-to-measure windows: casement, flush sash, sliding sash, tilt & turn, Georgian, and lead windows
- Doors: uPVC, composite, bi-fold, French, patio, and internal doors
- Conservatories: Victorian, lean-to, gable-end, Edwardian, and Georgian designs
We are FENSA-accredited, offering a 10-year warranty on all installations with an insurance-backed guarantee. Our Milton Keynes showroom allows you to explore products, colours, and finishes in person, while our friendly team provides free 3D design plans to help you visualise your project.
Ready to upgrade your windows for energy efficiency, style, and compliance with the new 2026 building regulations? Contact us today on 01908 507 778 or info@crownwindows.co.uk to discuss your requirements and book a free consultation.
