uPVC Box Sash Windows

Quality uPVC Box Sash Windows designed & manufactured in the UK


Vertical sliding box sash windows offer slim sight lines, a large glass area, a wide range of design options and flexible solutions for period properties or new build. This window style originated in the 17th century and continues to offer elegant glazed opening solutions with optimum ventilation and practicality guaranteed.

The KAT Classic is modern, secure, virtually maintenance free and manufactured from high impact, durable uPVC. uPVC box sash windows authentically replicate the look of timber but are virtually maintenance free. They are hand crafted to your dimensions, using very similar skills and techniques to those employed in a joinery workshop.

The thermal properties of uPVC are excellent and these windows can be supplied in a wide range of finishes. From six feet away it is extremely difficult to tell if the window is timber or uPVC.

Key features of uPVC Box Sash Windows

  • Virtually maintenance free
  • Will not stick, rot or warp
  • 128mm front to back frame depth
  • 150mm integral cill
  • Spiral sprung balance mechanism
  • Key locking cams with suited sash lifts and ring pulls
  • Fitted with draft excluding woolpile and seals
  • Low emissivity 24mm double glazed argon filled sealed units
  • All frames made to measure
  • Window energy rating of C as standard
  • Max width 1500mm x max height 2350mm
  • U Value 1.4 - 1.6 W/m2K

Our standard finish is Smooth White both sides.
The following finishes are available:
White Grain
Golden Oak
Irish Oak
Chartwell Green
Anthracite Grey (RAL 7016)
Agate Grey
English Oak
Nut Tree
Smooth Grey
A wide range of RAL finishes are also available.
General Description
A fully welded, vertical sliding sash window, designed to replicate Georgian and Victorian box sash window designs, also known as 'sash and case' windows in Scotland. Every Classic window is handmade to bespoke sizes and is also available with a mechanical joint.
24mm (4-16-4) double glazed sealed units
Planitherm Total Plus Low Emissivity, soft coat glass
Argon filled units
Warm Edge Spacer (Black, White or Grey)
U value of 1.4 on A rated.
Hardware & Accessories
Heritage Locking or Non-locking Cam catch handles and lift pulls available in: White, Gold, Chrome, Satin, Black, Graphite, Bronze or Antique Bronze.

Safety Restrictors available in:
White, Gold, Chrome or Satin Chrome.
Must be installed in accordance with Glass and Glazing Federation Guidelines
Arched Frames
We provide a true arched frame with no welded joints in the frame. On swept heads and arched frames, the top sash will always be fixed.
150mm or 210mm integral cill
Run-through or plant-on horns
White, black or grey spacer bar
Deep bottom rail
Surface fixed Astragal bar or Internal Fret available
Spring loaded travel restrictor
Tilt-in facility on both sashes (note: with a Woodgrain finish externally and Smooth finish internally we are not able to offer top sash tilt facility)
Arched head frames
Trickle ventilator
Fire Egress
PAS 24:2016 and Secured By Design security is available. (PAS24 is usually mandatory on new-build properties).
The upgrade includes:
Reinforced Tilt Latches
High Specification Cam Catch Receiver
High Specification Cam Catches and
Top Sash Security Blocks

Kitemarked to BS EN 12608
Product Reference
Fully welded or Mechanical jointed outerframe and sash
Mechanically jointed deep bottom rail option
128mm outerframe with integral cill
Black gasket on bead. Colour coded woolpile.
Spiral spring balance mechanism
System Parameters
Maximum Width 1,500mm
Maximum Height 2,350mm
10 year warranty on all PVCu profiles
10 year warranty on spiral balances
1 year warranty on hardware and accessories
Window Energy Rating
As standard, our Windows achieve a Window Energy Rating of B. Window Energy Rating A can be achieved.



KAT only supply bespoke windows to your exact specification. Each window is carefully designed and engineered to either replicate the authentic period features of an original design or to produce a contemporary window with a modern twist.

You choose the style, frame shape, hardware colour, glazing and other special features including authentic Georgian Bars to suit your property. We also offer ‘the solution’ for sensitive period buildings and for properties in conservation areas’. Our market leading box sash windows come with an extended 10 year warranty and design and engineered testing has demonstrated they have a life expectancy in excess of 25 years.



Material Information


All uPVC sections are extruded from high impact durable uPVC in accordance with BS7413. We have a wide range of timber alternative grained finishes and we can paint with almost any RAL colour.




All KAT box sash hardware is made in the UK. There are a number of options to choose from sash lifts, locking cam catches, safety restrictors and D handles.

Please consider your choice of ancillary hardware carefully because that is what you will eventually notice most when your products are installed. Choose from one of our suited finishes on our ring pulls and catches because it is attention to detail that helps make this unique product range so exciting.

Heritage Catches available in: –

  • White
  • Gold
  • Chrome
  • Satin
  • Black
  • Graphite
  • Bronze
  • Antique Bronze




Safety & Security


Our box sash windows are designed to discourage a determined intruder, and can be manufactured to meet Secure by Design or PAS 24:2016 standards.

Safety & Security

Colour Options


A little time and care with your choice of colour is advised and your selection should be influenced by the style of your property, surrounding architecture or your others windows and doors.

Colour options: –

  • A smooth White finish
  • White Grain
  • Cream
  • Golden Oak
  • Irish Oak
  • Rosewood
  • Chartwell Green
  • Anthracite Grey
  • Black
  • Agate Grey
  • English Oak
  • Nut Tree
  • Smooth Grey

Or choose from a wide range of RAL colours