September 18, 2017

Top 10 FAQ’s about the Descending Window System

Written by Rebecca Clayton

Strandweg 2 8806 Bäch, Hirt Metallbau
HIRT Swiss Descending Windows HIRT Swiss Descending Windows

How large can my descending window be?

As large as you need! There are two sizes of Descending Window.

The SF90 can be up to 18m2 per unit with a maximum carriage weight of 1500kg. This maximum size must be considered alongside the maximum dimensions of 6m wide and up to 6m tall.

The SFXL system can be much larger. It has been fully tested up to 6m tall x 12m wide per unit offering a maximum area of 40m2 with a maximum weight of 3500 kg. However, this system is able to be designed into impressive and bespoke installations where required. The largest descender front to date is 20m wide and weighs 7500 kg!

 SF 90SF XL SF Special
Max. Height6 m6 mUnlimited
Max. Width6 m12 mUnlimited
Max. Area18 m240 m2Unlimited
Max. Weight1,500 kg3,500 kgUnlimited


How are the descending windows operated? Do you use a switch?

The sinking façade system is electrically operated and can be controlled using a variety of methods to suit the technology of your building.

A deadman’s switch is the simplest control solution and is included with the system as standard. The switch is normally fixed to a wall and has to be installed within viewing distance of the descending front. The user has to visually monitor the opening as it opens and closes to ensure that there are no obstructions to its movement. If you take your finger off the switch the HSDW will immediately stop moving.

A more advanced control solution can be created with the introduction of sensors and photocells within the automated opening. The sensors and additional safety equipment monitor the opening during lifting and descending to make sure that it is unobstructed. That allows you to activate the facades movement with a single push of a button. The control equipment can then be integrated into your larger smart home technology system to be operated via smart apps if you want.

When the sinking windows are open what will the threshold look like?

This threshold combines safety, comfort and state of the art design. The insulated aluminium profile that emphasized the grooves is anodized colourless. Custom-made products with wood, stone or other materials are available.

Threshold of the HIRT descending windows Threshold of the descending windows SF XL

Threshold of the HIRT descending windows Threshold of the descending windows SF 90

How much space do I need below the floor?

When the windows sink below the floor they need somewhere to go. This area is known as the ‘parking space’. It is here that the glass elevation is housed when the doorway is open and where the motors, counterweights, the drive shaft, the compressor and the pneumatics are housed.

For the SF90 version this ‘parking space’ has to be the height of the window (H) plus 525mm with a minimum height of 2500mm. When using the SFXL version of the sinking façade this ‘parking space’ must be the height of the window (H) plus 1660mm.

How much space do i need for the HIRT descending windows? How much space do I need for the HIRT descending windows?

How do you deal with drainage and rainwater?

When the elevation is closed the Descending Window offers unparalleled water and air tightness thanks to its four-part pneumatic seal. The inner seal is a cleverly designed system of press and labyrinth seals. When operated via a control pulse they expand, completely sealing the opening. Additional brush seals remove any deposit build-up in the framing and offer a neat connection detail between the frame and sliding leaf.

A drainage or a pump must be installed within the ‘parking space’ to deal with the small amount of water that will be collected in the provided groove of the descender front.

Can I install a normal door system within the Descending framework?

Yes. Even windows.

By combining a 'traditional' window or door system into the sinking facade you can create an elevation that offers the best of all options. Use these normal windows and doors on a day to day basis but then open the entire facade whenever you want.

Solid doors, as well as facade systems, can be integrated into the sinking elevation to maintain design continuity on all areas of the building.

Incorporating doors and windows into the descending frame profile Incorporating doors and windows into the descending frame profile

How tall can the descending glass wall be?

You can create sinking windows up to 6m tall in both SF90 and SFXL options but the SF Special enables this height to be unlimited.

What options do I have for the glass within the sinking wall?

We can integrate an unlimited number of glass designs into the Swiss Descending Window. These specialist glasses include coloured glass, frosted glass, double and triple glazing as well as highly technical electrical glasses like heated glass, privacy glass and electrochromic glass.

Can I design the wall to sink down halfway and use it as a balustrade for upper story rooms?

The Descending walls can be programmed to partially sink down to the required balustrade height. You can then integrate a structural glass balustrade into the opening designed to withstand the required line loading.

How much does a Descending Window cost?

Descending windows are very much a bespoke product. However, as a guideline, the starting price would be £85,000 based on a 6m x 3m unit.

For additional options on making walls of glass disappear you can read our article "4 Ways to Create a Wall of Glass that Disappears"