SAPA Si Windows

Capital Windows have over 40 years experience manufacturing and installing an exceptional range of windows, doors and associated products. Whatever the project, we have the right approach and materials for the perfect finish.

SAPA Si Windows

Capital Windows manufacture and supply the sophisticated and long established SAPA Dualframe Window system.  We have been manufacturing and installing Dualframe windows and doors in many homes and properties. Designed to meet stringent building regulations and offering exceptional levels of security and weather performance, they are ideal for any type of home as a direct fix replacement window.

Dualframe Is A Contemporary Collection Of Windows Ideal For The Modern Home

In choosing the SAPA Dualframe System from Capital Windows you are benefiting from an advanced window range giving you ultra slim window sections, impressive appearance and elegant looks.

Large range of profiles | Excellent thermal properties – There is a large range of profiles that enables us to work with you on providing exactly the right window for you.  Whether you require chamfered, softline, ovolo or flat profiles for outer frames and opening lights with the flexibility for either internally or externally glazed windows.

Dualframe Windows also benefit from excellent thermal characteristics and full integration with other SAPA aluminium products to create glazed screens, one off designs or any other type of window arrangement.

A Choice Of Window Products

The Dualframe system is available either in standard or Si configurations.  The Si version of this highly successful door and window system offers you the ultimate window in terms of thermal performance, exceeding the current regulations for U Values.

If you are looking for maximum thermal efficiency and energy performance, the Dualframe Si suite is perfect for you. Both Dualframe and Dualframe Si windows are a 75mm direct fix window for the replacement of old windows or for new builds such as home extensions. Both utilise the very latest in thermal break technology meaning you can achieve impressive U values without complex glass specifications saving you money.

A Choice Of Window Opening Options

All Dualframe Windows are available as Casement top hung or side hung, tilt and turn and pivoting reversible windows. Other features of our market leading Dualframe window include:

  • Kitemarked to BS7950 for security
  • Can achieve an ‘A’ Window Energy Rating
  • Can be internally or externally beaded
  • Meets Secured By Design specification
  • Can be used with aluminium doors to create glazed screens

The Advantages Of Powder Coated Aluminium

Benefitting from all the advantages of durable and colour retaining powder coated aluminium, your new Dualframe windows are available in high quality white gloss, contemporary grey and a choice of over 200 other colours. You can choose from satin, matt or gloss shades as well as metallic effects and even different colours inside and out.

Whatever your requirements and wishes, the Dualframe suite of windows is expertly manufactured, professionally installed and will give you one of the best aluminium window systems you can buy today.


Established in 1979, Capital Windows Ltd provide the biggest choice of home improvement products from the leading names and systems companies.