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Thermal Break Aluminium Windows


Klosen / Aluminium Windows / Thermal Break Aluminium Windows

Aluminium Windows on Old Brick House
Slimline Window in Kitchen
External view of house with timber slimline bifold doors



Want only the best for your home? Our cutting-edge range of thermal break aluminium windows are exactly what you’ve been looking for. Combining stunning looks with impressive thermal efficiency and unparalleled durability, these windows really are the best of the best.

Whether you’re planning to modernise your property or are trying to maintain a period look while incorporating the latest technology, our range really does have something for everyone. A variety of designs and finishes are available to choose from, including powder-coated finishes in hundreds of different RAL shades.

As one of the UK’s leading specialist installers of aluminium windows and doors, our team has the know-how to supply and install them efficiently and to a high standard: we won’t settle for anything less than a flawless finish.

What’s more, each installation we carry out comes with a complimentary 10-year warranty. So, if you’re looking for a company you can count on – not just now, but in the years to come – look no further than Klosen. To find out more, download a brochure or request your free quotation today.

Why Choose a Thermal Break Aluminium Window?


Want the contemporary-yet-timeless look of an aluminium window, but the efficiency of PVC frames? Thermal break aluminium windows are the solution to your dilemma.

Pioneered by the British firm Senior Architectural Systems, this ingenious feature really does give you the best of both worlds. In thermal break windows, polyamide material is sandwiched between the inside and outside of the aluminium frame, creating an insulating ‘barrier’ between both panels. The result? Temperature conductivity is slashed, allowing the window to much more effectively keep heat in and cold out – perfect for keeping energy bills in check.

As an added bonus, your home will be cooler in the summer. Noise from the outdoors will find it harder to make its way inside too, giving you a more peaceful home than ever before. Aluminium thermal break windows are simply the best of the best.

Contact Us Who We Work With

Our Customer Reviews

Great Price & Quick Delivery

This company have been amazing and came to our rescue when another company let us down repeatedly over a period of 4 months during our building work. We got a great price, a quick delivery time and the same product but this time with lovely fitters who knew exactly what they were doing. Now we will will have a warm house for christmas HOORAY !! We went for 3 large sliding doors and the quality of the product is excellent . Many thanks to Audrey Cieran and the team I would recommend highly
- Esther Young


Delighted with the product and the service provided by Klosen. The installation team were excellent and very helpful.
- Sara Hyem

Very Happy

We’ve been very happy with the work Klosen recently completed for us. They installed a variety of windows and sliding doors for us on our new build project. All of the information we requested early on was provided promptly and they were great with our architect. Very happy with the end result and the colour they helped us chose.
- Sarah Munton

Brands We Work With

Based on our extensive knowledge and experience, we’ve hand-picked two of the world’s best window suppliers: Cortizo and Senior Architectural Systems. Learn more about each brand below or download a brochure for further information.

Cortizo logo
Senior Architechtural Systems Logo


Cortizo, a renowned company based in Spain, has established itself as a leader in the industry through its unwavering commitment to excellence in aluminium products. Cortizo produces window frames that are unparalleled in their sleek, minimalist aesthetics. Cortizo has carved out a unique niche for itself, establishing a reputation as the go-to source for architects, designers, and homeowners seeking aluminium products that are quite literally a cut above the rest.

Our Cortizo Projects

Working across the UK to improve both the functionality and aesthetics of properties, Klosen has a proven record of enhancing homes with Cortizo products. At Tow Top in Cumbria, we used slim aluminium windows for unobstructed views and a modern look, allowing for the transformation of the building’s exterior.

We also installed Cor 70 Hidden Sash Tilt and Turn windows to May Cottage in Peterborough which improved the overall facade of the residence whilst boosting practicality as it provides good levels of thermal insulation and reduces noise levels.

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Cortizo Specifications

Transmittance: Uw ≥ 1.0 (W/m2K)

Acoustic insulation: Rw up to 45 dB

Air permeability: Class 4

Water tightness: Class E1200

Wind resistance: Class CE 2400

Security test: PAS24 passed

10 Year Guarantee

We offer a 10 year guarantee on all aluminium profiles and 25 years for the powder coating element

Thermal Efficiency

Stay warm in the winter and cool in the summer whilst cutting down on energy bills

Complete Flexibility

Our team are flexible throughout the entire process, including the design and installation of windows

25+ Years Experience

Klosen have over 25 years experience working with designers, architects and homeowners

Senior Architectural Systems

Located in the Yorkshire city of Doncaster, Senior Architectural Systems is one of the world’s leading manufacturers of aluminium windows. It earned that reputation by never resting on its laurels and continuing to push the boundaries of what’s possible; the fact that it invented the polyamide thermal break pretty much says it all!

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Modern house painted white with wooden panelling and trees behind

Senior Architectural Systems Specifications

Typical sizes:
Width (mm)

Height (mm)
x 1500

Thickness: 28mm – 50mm

Air Permeability: 600 Pa
Water Tightness: 600 Pa
Wind Resistance: 2400 Pa

Residential CEN Standard:
1230 x 1480 28mm Double Glazed Unit: 1.24 W/m2K

Tested to PAS24, BS6375-2 and BS6375-3

Typical sizes:
Width (mm)

Height (mm)
x 1400

Thickness: 28mm – 44mm

Air Permeability: 600 Pa
Water Tightness: 600 Pa
Wind Resistance: 1600 Pa

Residential CEN Standard:
1230 x 1480 28mm Double Glazed Unit: 1.40 W/m2K

Tested to PAS24, BS6375-1, BS6375-2 and BS6375-3


We made it onto an episode of Grand Designs, with a Kevin McCloud-approved home project in South Lincolnshire. We supplied Cortizo casement windows for this impressive Dutch-inspired barn. The contemporary windows on the facade are certainly a standout feature.

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Areas We Cover

Based in Market Deeping, Lincolnshire, we cover towns and cities within a 60-mile radius, including the entirety of Cambridgeshire and Lincolnshire. Areas we regularly visit include Peterborough, Bourne, Stamford, Huntingdon and London.

Why Choose Klosen?

  • Over 25 years of experience
  • Five-star reputation
  • 10 year guarantee on all work as standard
  • No project is too big or small
  • Experience working on high-profile projects, including a Grand Designs home and the ABBA Arena in London
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Do all aluminium windows come with a thermal break?

No, not every manufacturer offers this technology. All of the windows we supply come with it installed, however. We highly recommend choosing thermal break windows for the efficiency benefits they provide.

Are aluminium window frames more durable than PVC or wood?

Yes, significantly so. Aluminium won’t rust, corrode, crack or rot, making it the perfect material for this application.

What colours are your windows available in?

Any colour you can imagine! Besides standard shades of white, grey and black, our windows are available in hundreds of RAL hues, allowing you to get creative

Get in touch with us today to receive your free quotation!