Double Glazed Windows
Supply Only | Supply & Fit
Double glazing has become the modern standard for UK homes, particularly for homeowners investing in high quality replacement windows that improve energy efficiency, comfort, and security. It works by combining two panes of glass within a single sealed unit to improve insulation and performance. With British properties facing considerable heat loss through traditional single glazing and rising energy costs impacting household budgets, double glazing has become an essential upgrade rather than a luxury feature.
Whether you own a Georgian townhouse, Victorian terrace, or a home with distinctive Edwardian windows, we offer double glazed windows in uPVC, aluminium, and timber across a variety of styles and colours. All double glazed windows are made in Britain with 10 years of Guarantee.
Our Double Glazing
Styles & Material
Our Double glazed windows are available in three primary frame materials uPVC, Timber, and Aluminium each offering distinct advantages in performance, design flexibility, and long-term maintenance.
With the range of different styles and colours in each material our double glazed windows comes in sash windows to keep traditional and heritage look, casement windows, flush windows, bay windows, tilt and turn windows for easy cleaning. All our double glazed windows are energy efficient and requires low maintenance.
Following are our double glazed windows in casement style, we offer flush casement, cottage-style, or shaped windows, allowing seamless integration into both traditional and contemporary homes. All our double glazing windows are available in Aluminium, Timber and uPVC material in the variety of different colours.
Secondary & Decorative Glazing
In addition to our double glazing windows, at Colin’s Sash Windows we also offer the secondary glazing for listed buildings and conservative areas where double glazing is not permitted. And with this we also offer the decorative glazing with the different options available in obscure glass to enhance privacy and coloured glass to make your home more charming and colorful.
Our Double Glazing Unit Composition
Our standard double glazed window uses two 4 mm glass panes with a gap of 12–20 mm between them, making the whole unit 20–28 mm thick. The width of this gap is a balance; a wider space is better for insulation and blocking noise, but it requires a deeper frame, which can look too bulky, especially in older homes.
The type of glass you choose also makes a big difference. Clear glass gives you the best view and lets in the most light, while tinted glass can help reduce unwanted heat from the sun. For even better performance, a special Low-E coating can be applied to the glass. Where this coating is placed depends on your main goal: to either let in more solar heat or to keep your home’s warmth from escaping.
Gas Filling and Thermal Enhancement
The gas sealed between the panes of glass is key to our window’s insulation. Instead of air, the space is often filled with Argon gas, which is about one-third better at keeping heat in because it’s less conductive. It’s a safe, clear, and fairly affordable gas found naturally in our atmosphere.
By reducing conduction, convection, and radiative heat loss, gas-filled units deliver a measurable improvement in comfort and energy efficiency.
Double Glazed Windows
BFRC Energy Rating Comparison
The British Fenestration Rating Council (BFRC) rates windows using an A++ to G scale.
Our double glazed glass windows achieve competitive ratings across all three materials which is uPVC, wooden and aluminium. All our double glazed windows are independently tested by BFRC and rated afterward. The purpose of this information is that you should know about energy efficiency before replacing or buying new windows. Check the windows energy effciecy ratings below.
| Window Material | Typical BFRC Rating* | Typical U-Value (W/m²K) | Performance Notes |
|---|---|---|---|
| uPVC | A – A+ | ≈ 1.2 – 1.4 | Multi-chambered uPVC profiles with Argon-filled double glazing and Low-E glass usually deliver the best overall insulation and energy efficiency. |
| Timber (Wooden) | B – A | ≈ 1.3 – 1.5 | Timber is naturally insulating and ideal for conservation and period properties. Performance depends on timber thickness, glazing specification and external paint or stain finish. |
| Aluminium | B | ≈ 1.4 – 1.6 | Modern aluminium frames use thermal breaks to achieve good U-values. Slim sightlines maximise glass area and light while still meeting current energy-efficiency standards. |
*Typical ratings shown for modern double glazed specifications. Exact BFRC ratings and U-values depend on final glass, spacer and frame configuration chosen for your project.
UK Building Regulation Compliance
Every double glazed window we supplied and install is engineered to meet or exceed the UK’s building regulation requirements for energy efficiency, security, ventilation, and thermal comfort. Because window performance varies by material, glass type, and installation detail, our specifications are designed to comply with the correct regulation for your property type — whether it is an older Victorian terrace or a newly built dwelling.
Part L – Energy Performance
Our double glazed windows are specifically manufactured to comply with Part L (Conservation of Fuel and Power).
Our specifications include:
- Replacement windows: 1.4 W/m²K or better
- New build installations (where required): 1.2 W/m²K achievable upon request
- Low-E glass fitted as standard for improved heat retention
- Warm-edge spacers to reduce thermal bridging and minimise heat loss
- Argon gas filling for superior insulation compared to air-filled units
- Precision-engineered perimeter seals designed to minimise air leakage and improve airtightness
You can use our Window Energy Rating Requirements tool
Document F – Ventilation
To comply with Document F, our double glazed windows can be supplied with:
- Trickle vents installed where required by Building Control regulations
- Optional over-frame trickle vent hoods specifically designed for sash window frames
- Night-vent secure positions available on casement windows to maintain airflow while keeping the window locked
- Correct equivalent ventilation area (EQA) sizing calculated to ensure compliance with Document F ventilation standards
You can use our trickle vent requirement calculator
Document Q – Security
For new-build properties in England, Document Q requires windows to resist common forced-entry methods.
Our qualifying double glazed windows incorporate:
- PAS 24-tested locking systems for enhanced protection against common forced-entry methods
- Reinforced frames available across uPVC, timber, and aluminium window options
- Laminated security glazing provided where additional impact resistance is required
- Anti-jemmy hardware upgrades to prevent levering or prying attacks
- High-security hinge-side protection to safeguard against hinge-side forced entry attempts
This ensures our windows meet the security benchmarks set by Document Q.
You can use our PAS 24 requirement calculator
Document O – Overheating Compliance
Where Document O applies (mainly new-builds), we can provide:
- Low solar-gain glass options available to limit excessive heat build-up during warmer months
- Tinted or solar-control glazing to reduce glare and minimise unwanted solar heat gain
- Optimised g-value selection based on your home’s orientation and room usage to achieve the correct balance of light and thermal comfort
- Recommendations to prevent overheating in bedrooms, living areas, and south-facing rooms according to Document O guidelines
This helps developers and homeowners meet overheating rules without compromising brightness.
Conservation & Listed Buildings Compliance
Many conservation areas restrict window replacements. Our double glazing solutions for such properties include:
If replacements are allowed:
- Slim-profile timber double glazing designed to replicate traditional window proportions while delivering modern thermal performance
- Profiles matched to original sash or casement designs to maintain heritage accuracy in conservation and period properties
- Putty-line or heritage glazing bar options available to closely replicate traditional single-glazed aesthetics
If replacements are NOT allowed:
- Secondary glazing that is fully reversible and widely accepted by most local councils for listed buildings and conservation areas
- Ultra-slimline IGUs designed for sensitive sightline requirements where maintaining original proportions is essential
- Colour-matched timber frames to replicate the appearance of existing windows and ensure visual consistency on heritage properties
FENSA / CERTASS Compliance
Every installation we carry out is self-certified through FENSA or CERTASS, ensuring:
- Energy performance compliance ensured through certified double glazed units that meet required U-value and BFRC rating standards
- Safety glazing compliance provided in accordance with Building Regulations for critical locations such as doors, low-level glazing, and bathroom areas
- Security and ventilation compliance verified under relevant regulations including Document Q and Document F
- Insurance-backed warranties covering workmanship and product performance for complete peace of mind
- Homeowner registration certificates issued through FENSA or CERTASS to document full regulatory compliance
This guarantees all work meets legal standards and ensures your home improvements are fully documented.
To Get Value For Money
Choose Colin's Sash Windows
10 Years Gaurantee
All our double glazed windows comes with the 10 years on parts and labour.
Made in Britain
We supply only made in Britain double glazed windows that are manufactured in UK.
We Match Your Price
If you have got a cheaper price from any other supplier then we are ready to match the price.
Our Double Glazed Windows Prices
At Colin’s Sash Windows, most of our double glazed windows are made to measure, so every project receives a tailored quote based on the exact size, material and glazing specification. This ensures every customer pays the right price for their home rather than a generic estimate.
To give a general idea of cost, our supply only uPVC units start from around £270 plus VAT. Fully specified and installed modern double glazed windows for standard openings typically fall between £980 and £1,500 plus VAT depending on the material, design and hardware selected. Larger windows, premium materials such as timber or aluminium and upgraded glazing options may range between £1,200 and £2,000 or more.
Unlike many suppliers, we offer fixed pricing for a wide range of common sizes which helps keep costs predictable and transparent. Once you share your measurements and preferred specification, we issue a clear and exact quote tailored to your project.
For an exact price, you can use our online double glazed windows cost calculator or simply request a free quote by sending an email at sales@colinssashwindows.co.uk and our team will guide you through all options with a detailed breakdown based on your property.
Calculate the Cost of Your Double Glazed Windows
Get a fast, accurate estimate double glazed windows in just 60 seconds using our double glazing cost calculator. No sign-up, no obligation – simply enter your details and see your tailored price.
Benefits Of Buying
Double Glazed Windows From Us
Buying double glaze windows from us means you’re not only getting new windows, you’re also securing all the added benefits that come with Colin’s Sash Windows. We aim to earn your full trust, which is why the advantages of our double glazed windows truly set us apart from other suppliers.
Energy Efficiency
Our double glazed windows use Low E coated glass, Argon gas filling and warm edge spacer bars to improve insulation and reduce heat loss. These features help most configurations achieve U values between 1.2 and 1.4 W/m²K. This provides better indoor warmth and lower heating costs compared to single glazing.
Security
Our double glazed units feature strong dual pane glass and reinforced uPVC, timber or aluminium frames for superior resistance against forced entry. Multi point locking is standard, with PAS 24 compliant hardware available for new build projects. This ensures long term security and protection for your home.
Condensation Control
The warm internal surface created by Low E glass, Argon gas cavities and warm edge spacers reduces the likelihood of indoor condensation. This helps prevent mould, damp and moisture damage. It also improves day to day comfort, especially in older properties.
Acoustic Insulation
Our glazing systems are engineered to reduce external noise by 20 to 35 decibels depending on the chosen configuration. Laminated or asymmetric glass options offer even greater sound reduction for homes in busy locations. This creates a quieter and more comfortable living environment.
Ventilation Integration
Our windows include trickle vents where required and offer optional over frame vent hoods for sash windows. Casement designs feature secure night vent positions that allow airflow without compromising security. All ventilation sizing is calculated to comply with Document F standards.
Unmatched Guarantees
Our double glazed windows come with comprehensive guarantees that give long-term peace of mind. Every installation includes workmanship and product protection designed to keep your windows performing at their best. This ensures your investment stays secure for many years.
Accreditations
Our products carry certifications from more than twelve recognised UK organisations for quality, safety and performance. These accreditations confirm that our windows meet strict national standards. They also provide reassurance that every unit is manufactured and installed to an exceptional level.
Largest Double Glazing UK Suppliers
Colin’s Sash Windows is among the largest suppliers of double glazed window in the UK. Our scale allows us to deliver consistent quality, reliable service and competitive pricing. Homeowners benefit from proven experience and systems trusted across thousands of properties nationwide.
Installation of our Double Glazed Windows
At Colin’s Sash Windows, we ensure a seamless window installation process starting with a thorough survey to take precise measurements, assess the opening, check structural issues, and confirm your choices (frame colour, hardware, glazing, etc.). We then carefully remove old windows, protect your home, clean and repair the opening, and treat any damp problems.
New windows are securely fixed using the correct method for your walls, fully weatherproofed with seals, and cavity closers for maximum insulation and no access to water. Finally, we carry out detailed quality checks on all functions and seals, refit trims, and hand over FENSA certification, warranty, and maintenance guidance, leaving you with perfectly fitted, high-performance windows and a clean, tidy home.
Real Images Of Our
Double Glazed Windows In UK Homes
Double Glazed Windows Buying Guides
Areas We Deliver
Supply and installation are available nationwide in most areas across the UK. Request a quote with your
postcode and project details to confirm survey dates and lead times. We have the lowest leads times of 2-3 weeks
approx. for double glazed windows
For delivery of our sash windows you can see the below image, in the green areas the delivery cost will be £36 and in yellow highlighted areas the delivery cost will be £120+ and for these areas please first talk to our sales team and then we will confirm you about delivery and with in red areas we don’t deliver our double glazing windows.
Ready to Get Started?
Design & order your bespoke double glazing windows with our team today. Share your sizes, material choice and any planning constraints. We will prepare a clear quotation and timeline, then book your survey.
Get in Touch At Once!
Feel free to call us on 01525 552131. Our friendly sales advisors will guide you through the ordering process and help you with anything regarding double glazed windows. Alternatively, don’t hesitate to write us via the contact form or directly to our email address sales@colinssashwindows.co.uk. Don’t waste your time and take advantage of the finest quotes throughout the UK and Ireland.
