Traditional box sash windows

The only airtight classical box sash window

The AP’s development innovation team has recently developed a range of bespoke box sash windows with unique features. Simple, effective and aesthetic AP have reinvented the box sash so that it really works.

Our traditional box sash windows in accoaya obtains an ‘A’ band BFRC Windows Energy rating. This is exceptional for a traditional, weight and pulley operated sash window. The key to this performance is AP’S discrete but effective TSC Weatherproofing SystemTM which achieves an effective air leakage ‘L’ Factor of 0,00 W/m²/K.

TSC Weatherproofing systemTM – How it works?

The AP box sash uses a unique jamb and casing profile creating a physical barrier or ‘decompression chamber’. Water is channelled in this zone toward drainage ducts running to the outer cill.

The unique profile and seal position create Total Seal Continuity.

A simple guide system assures frontal translation of the sashes during closing providing optimal seal compression.

When opened the sash returns naturally to the free position allowing effortless opening without seal wear.

This system not only allows the AP window to obtain excellent levels of waterproofing, insulation and soundproofing, but also guaranties a smooth running action whilst retaining the aspect of a traditional window.


A large selection of quality selected solid and laminated timber is available including Oak, Accoya and Scots Pine. Wood choice often depends on regional tendencies and individual preferences. Our advisors are more than willing to help with this choice.


All our box sash windows come fully finished with one primer coat and two coats of exterior water based finish.


Our standard range for double glazed windows comes with simulated divided lite glazing bars, with bar width options for 19mm, 24mm or 30mm. The exterior beads are assembled using mortice and tenon and form a structural part of the window. Interior beads are assembled as frames and mounted in our workshops to assure a perfect alignment with the exterior.

For our historical range True divided lite windows are also available upon demand for use with single glazing or extra thin double glazing.


  • Bicolor finish
  • Interior shutters
  • Mosquito screens
  • Integrated alarm sensors