FAQ's: Keller minimal windows® Sliding Doors

the most frequently asked questions

Keller minimal windows® are the premier choice for slim framed sliding glass doors. They are renowned for their exceptional frameless aesthetic, flush threshold and capabilities of large expanses of sliding glass. One of their main features is the ability to be completely frameless on all its outer edges which accentuates the impressive 21mm vertical sightline.

Due to the popularity of this glazing system, we receive a large number of questions, therefore we have put together a list of the most frequently asked questions to provide you with all the answers in one place…


  • How have these sliding doors been tested for performance?

minimal windows® sliding doors have been fully tested and certified at the Rosenheim Institute in Germany. They have been tested for Air Permeability, Water Resistance, Security and Resistance to Wind Load.

IQ Glass has also undertaken specific Hurricane testing for the minimal windows® 4+ system at the Vinci testing facility in Leighton Buzzard. Due to the large sizing abilities and triple glazing of these sliding doors, they are tested for certain weather resistances that the minimal windows® are not tested for. Hurricanes are not very common in the UK; however, it is wise to be prepared for severe weather conditions such as storms and very high wind loads.

This additional testing which goes far beyond any building requirements, ensures that the minimal windows® 4+ system is highly adaptable to harsh weather environments such as coastal or high-altitude environments.

  • How much do the minimal windows® sliding doors cost?

The price of a minimal window must be calculated as per the installation. The general guide price we advise for standard minimal windows® calculates at approximately £1000 per m2. For the minimal windows® 4+ system (triple glazed), the cost has an approximate uplift of 20-25% depending on the size, location and glass specification.

Please note that these are guide costs only. We strongly recommend allowing our estimating team to calculate the glazing cost for your project at a budgeting stage.

Photography Credit: Quintin Lake
  • How does the locking work?

The minimal windows® system has been fully tested for Burglar Resistance in accordance with EN 1627 (a European Regulation). The locking system used on a minimal window® system will largely depend on the way in which the doors will be used as well as the configuration of the doors.

Multiple locking solutions are available:

Standard Locking: a multi-point lock which is operated via an internal thrust level handle.

Internal Key Locking: a multi-point lock which is operated via an internal removable key.

Electromagnetic Locking: operated via a remote, wall switch, smartphone application or integrated into a smart home system.

External Key Locking: a multi-point lock which is operated via an external removable key.

  • What base options are available?

There a 2 base track options available with the Keller minimal windows® sliding doors:

The Flush Track – with an aluminium base frame 38mm deep which sits below the finished floor level.

The Freeway Base – This provides a completely flat and flush base track providing a visible framing of approx 37mm above the finished floor level.

IQ Glass has designed a series of bespoke drainage systems for the minimal windows® sliding doors that sit below the base of the frame. The base tracks have outlets that drain any water through the base frame and onto our unique solid Neoprene drain block under each sliding door unit. Water is then forced outside by the drainage block into a specified drainage channel.

  • What is the lead time?
The lead time for the minimal windows is 10-12 weeks from approval of the design drawing, initial drawings can take up to 20 working days (large projects may have a longer design time).
  • What is the U Value?
As standard, this system comes double glazed, based on the specification the system is able to achieve a Uw value of 1.4 W/m2K. This can be reduced to 0.8 W/m2K with an upgraded triple glazed system.
  • What makes minimal windows® unique?
The framing of the Keller minimal windows® sliding doors can be hidden to provide a minimalistic sliding door design that offers barely visible framing. They boast a vertical sightline of just 21mm, and the outer framing can be hidden behind internal plasterboard and external render.

Unlike some ‘slim’ sliding systems you do not get any visible frame above the finished floor level. This creates a full floor to ceiling glass finish.

Available in both double glazed (minimal windows®) or triple glazed sliding door system (minimal windows® 4+) these large sliding doors can hold up to 12m2 of glass in a moving panel.

These sliding doors have been fully tested at the prestigious Rosenheim Institute in Germany, for Security, Air Permeability, Water Resistance and Resistance to Wind Load – which achieved excellent results for such a slim framed system.

Whereas some aluminium sliding doors are designed to reach the basic performance criteria for building regulations minimal windows are designed to surpass this, offering excellent quality and performance all with an ultra-minimal frame.
Photography Credit: Tony Timmington
  • How is the outer frame hidden?
minimal windows® offer a completely frameless look to all the outer edges of the system. This is done by hiding the external fixed frames within the building finishes.

Internally, the minimal windows® can be hidden by plasterboard which is installed by the builders after installation. Whereas externally, the fixed frames can be hidden by render or cladding. They can also be hidden behind the external brickwork skin (if the brickwork is prepared correctly), we can create drawings to show exactly how this is possible.

All internal and external finishes to hide the framing must be installed after the sliding doors have been fitted.
large sliding doors
Ashley Road (Architect: Dyer Grimes Architects)
  • Can the sliding doors be manufactured in a choice of colours?
The minimal windows® system can be Polyester Powder Coated (PPC) in any classic RAL colour and can also be manufactured with an anodised finish – which provides a specialist metallic finish.

When a property is 5km away from the sea or if the minimal windows® are to be installed within a high moisture environment (like a swimming pool), then the frames will need to be finished with a marine grade finish.
  • What is the maximum size of each sliding door?
The minimal windows® have a maximum pane size of 8.5m2. There isn’t a maximum pane width for the minimal windows® sliding doors, but the maximum pane height is 4m.

Larger panes of glass are available with the minimal windows® 4+ sliding doors which offer a maximum tested pane height of 4.5m and a maximum pane size of 12m2!
  • Are there various methods of ventilation?
The minimal windows® sliding doors can be vented using a unique slot-aeration that consists of a 3-hole base and head sleeve to ensure the continuous exchange of air locking. The lock can be positioned at 20mm or 40mm to allow significant airflow while preventing unwanted access.

If you have any other questions about minimal windows® sliding doors, then visit the minimal windows sliding doors pages on our website or call us to arrange a showroom visit where you can views the system in person and talk through your project with our showroom staff.

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