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Thermal Break Aluminium Windows


Klosen / Aluminium Windows / Aluminium Fixed Windows

Aluminium Windows on Old Brick House
External view of timber slimline bifold doors



The perfect complement to our wider range of aluminium windows and doors, our stunning fixed aluminium windows offer exemplary thermal performance, long-lasting durability and an ultra-modern design.

Perfectly matching the appearance and profile of our bifold doors and casement windows, these energy-efficient items will transform the look of any home. Whether you’re looking to modernise your property or maintain its historic appearance while incorporating modern technology, aluminium windows are exactly what you’re looking for.

The experienced and friendly team at Klosen can supply, deliver and install your windows efficiently and flawlessly. Whether you’re shopping for your home or business premises, we’ll work around your schedule to complete the job with minimal disruption.

And best of all, every installation we complete comes with a 10-year guarantee, giving you complete peace of mind for many years to come.

To find out more, download a brochure or request your free quotation today.


Why Choose a Fixed Aluminium Window?


There are a number of reasons why homeowners are increasingly choosing aluminium windows over standard PVC frames. Aesthetics are high on that list; aluminium fixed windows are beautiful to look at thanks to their sleek, modern designs – designs that somehow manage to be both timeless and cutting-edge.

They have a number of practical benefits, too. Because aluminium doesn’t rust, crack or go brittle over time, aluminium frames can far outlast PVC ones. They’re stronger too, which allows the frames to be thinner without compromising on security. That means more light into your home and a greater feeling of space than you’ve ever had before.

Plus, modern aluminium frames are now more efficient than ever. Advancements like polyurethane foam thermal barriers keep the heat in and the cold out, helping you live comfortably all year round. And with a near-limitless range of colours and finishes to choose from – including powder-coated RAL shades – it’s easy to find a look that complements your property.

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

As one of the UK’s leading aluminium door and window specialists, it’s safe to say that we know the industry inside out. We’ve used that experience to carefully hand-pick brands and products that we know you’ll love.

The products we supply come from renowned suppliers Cortizo and Senior Architectural Systems, two of the most highly respected manufacturers on the planet.

Discover more about each brand below or download a brochure for further information.

Cortizo logo
Senior Architechtural Systems Logo


Spain’s leading manufacturer of aluminium doors and windows, Cortizo, has been in the industry for decades. Specialising exclusively in the manufacture of aluminium products, Cortizo knows how to get the best out of the material – which is why its frames are so thin and stunning to look at.

Klosen has worked across the UK, installing Cortizo windows to enhance both commercial and residential properties. One of our projects was based in Queens Street, a commercial property in Peterborough. We implemented steel-framed windows to mimic the original Crittall design. Acoustic laminated glass was used to reduce noise from nearby restaurants and bars. This was a project that enhanced both functionality and aesthetics.

This was not our only successful endeavour, check out our projects and case studies for our quality Cortizo solutions.

Find Out More

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

Doncaster-based Senior Architectural Systems is a company known for its restless commitment to innovation. With over three decades in the industry, the British manufacturer has been responsible for a number of technological breakthroughs over the years.

These include the polyurethane foam thermal barrier and powder coated finishes with no-quibble guarantees.

Find Out More
double fronted house with feature stonework and driveway

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


Our specialism in aluminium doors and windows has led to us being involved in some pretty remarkable projects over the years. One that stands out, however, is this Dutch barn-inspired dream home in South Holland, Lincolnshire.

The owners chose us to install a variety of doors and windows from Spanish brand Cortizo, renowned the world over for its striking designs. Our work didn’t just bring the owners joy – it was noticed across the country in 2021 thanks to the home’s appearance on the popular architecture show Grand Designs.

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
Contact Us


Does the installation process differ compared to PVC windows?

No, the installation process is pretty much the same – the only real difference in cost comes from the frames themselves.

What finishes do you offer for the window frames?

Besides standard finishes like white, grey and black, our suppliers allow you to choose from hundreds of RAL colours. These can be applied using powder coating, resulting in a durable finish that won’t chip or flake off.

What are your lead times for an aluminium fixed window installation?

Approximately five to six weeks from enquiry to installation, although this may change depending on which windows and finishes you choose.

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