Should I choose a Two or a Three Panel Sliding Door?

How many panes should I have in the opening?

Typically, with thicker framed aluminium sliders, you would look to use the largest panel sizes possible and minimise the amount of frame you have in your aperture. With the advance of slim framed systems like minimal windows, this is much less of a consideration. Thanks to the very minimal framing the panel junctions don't have as much disruption to views out or in, so you can dissect an aperture with more sliding panes.

The number of sliding panes you choose within the doorway then becomes a personal or design choice. Here we will look through the major considerations for whether you opt for a two or three-pane slider.

Size of Clear Opening

With non-pocket sliding doors, you will always have a static pane within the opening where the sliding units sit and stack when open. The number of sliding panes or sliding tracks you have will then determine how much of your glass doorway is 'open'.

For example, if you chose a two-pane sliding door you would get an opening of 50% when the sliding pane is open. If you chose a three-pane sliding door you would get an opening of 66% when the sliding panes are opened and stacked.

In theory then the more sliding panes you have in the doorway the larger your usable gap is when the doors are slid open. However, you will have to keep in mind the parameters of the system you are using to ensure the sliding doors work well and you should look to create a balance in the design. Having too many sliding panes crammed into a small opening will look messy and will be difficult to operate.

For instance, the contemporary rear extension of a traditional house had a clear opening trough the outdoor sitting area. The two-track 21mm sightliness sliding glass doors provided a bigger glazing experience with wider glass panels when closed. Therefore, the homeowners have a ‘movable’ glass wall to allow more natural light into the brand-new kitchen extension.

Specification Considerations

Slim Sliding doors have a minimum width to height ratio of 1:3, that means that the width of the sliding pane cannot be less than a third of the height for example. If the sliding doors were 3m tall each pane couldn't be narrower than 1m.

• Our recommended maximum track depth is 4 tracks. Systems with more than 4 tracks have a very deep threshold of over 30cm and the sliding stack will be very heavy to operate manually.

For door openings that over over 3m wide both a two-pane and three-pane sliding door would work well. For door openings below 3m wide, we would recommend a two-pane sliding configuration (or a pocket door).

When you select a two-pane sliding door your sliding configurations are basically limited to:

• One sliding to the right over one fixed
• One sliding to the left over one fixed
• Both units sliding (note that you will still only be able to open one half of the opening at any one time).

Whereas with a three-pane sliding door you have more sliding units and therefore a larger array of configuration options. 
Some of these include:

•  Two sliding to the right over one fixed
• Two sliding to the left over one fixed
• All three sliding (this gives you the option to slide and stack the panes to the right, to the left or slide the two outer panes over the middle unit)
• Two fixed outer panes with a central sliding unit (results in a two-track, three-pane system)

If you are looking for a larger range of sliding configurations to choose from then a three-pane sliding door may be more suitable. 

Track Depths

Generally (apart from some sliding configurations, as listed above) you would have one track for each pane within your sliding door system. That means the resulting depth of frame (from front to back / inside to outside) will be bigger the more panes you have.

Depth of system for minimal windows:

Number of Tracks	minimal windows® depth	minimal windows® 4+
1	60mm	79mm
2	120mm	174mm
3	185mm	269mm
4	240mm	N/A

If you are looking to reduce the depth of the sliding door framework then using fewer panes is the easiest way to do that (alternatively there are ways to play around with the sliding configuration to achieve a two-track system with more than two sliding panes. Speak to the team for further advice).

As each sliding unit in the minimal windows^® system can be up to 8.5m² (or 12m² in the minimal windows^® 4+ large sliding door system) you can easily fill a very large doorway with only two sliding panes if you wanted a shallower framing threshold depth.

To be able to have the right framing track depth according to the building, a combination of two and three-pane sliding glass door can be used in different location of the house like minimal windows installed in the coastal new build house in Mawgan Porth.

What is your Preferred View?

Although the frame of a slim sliding system has a minimal interruption to views of sightlines there will still be an element of the frame where any sliding units meet. Thinking about what will actually be viewed from within the space through the doors can help you choose the number of sliding panes you want to use.

With a two-pane slider, the vertical framing will sit right in the middle of the opening. This could cause a small element of visual distortion to beautiful vistas or landscapes outside.

For projects looking to capitalise on views out of their sliding doors, a three-pane solution might work best. As the centre of the opening is a large glass pane you will maintain a clear view from the middle of the doorway, which is where your focus is naturally drawn.

What About a Pocket Door?

A sliding pocket door configuration may be the answer for you if you want to satisfy both the requirement for a clear aperture when open and fewer sight-lines when closed.

The consideration of track numbers is still relevant for both pocket doors as you must allow space for each track within the wall space (see table above).

The more sliding panes you have in a pocket door system the larger the cavity within the walls needs to be. If you are limited on available wall thickness or space, you may want to opt for a two-pane sliding pocket door.

Or you may build and exterior wall extension to have enough space for three track sliding glass doors as pocket door like the project Waldegrave. The modern extension in London house connected with the garden by three-track slim sliding glass doors which can be hidden in the wall.

An Architects View

minimal windows sliding doors are the preferred sliding door choice for architects all over the UK who use these high specification glass doors on projects time and again. Holland Green architects have used the minimal windows system on many of their projects. Laira Piccinato offered the below advice for choosing the configuration of the sliding doors on your project:

• Consider how the circulation of the space works in relation to the doors, i.e. how you want to access your outside space.
• What are the proportions of the facade? Are there features on the facade that you want to complement via the sightlines of the frame of the doors? It is these little details, continuous lines and symmetry will ensure that the design of the facade looks well thought through and aesthetically pleasing.
• You also need to consider the deflection of the beam above. Very minimal systems have small tolerances for deflection so you need to make sure that the structural opening is formed in conjunction with these in mind.

So would she recommend a two or three-pane sliding door on a project?

"It depends on the dimensions of the aperture to be glazed and also the alignment along the wall (i.e. whether filling it, or only part of it). If they are central, then would not go for 2 as wouldn't want a visual break down the middle of the room. I would prefer a clear view through a central pane of a 3 pane arrangement."

In Conclusion

A two-pane sliding door is suitable for:

• Openings up to 17m² overall (or 24m² in the minimal windows^® 4+ system)
• Openings under 3m wide
• Doorways where you want to limit the number of tracks
• Apertures where you want to maximise the glass pane sizes (use as big a pane of glass as possible).

A three-pane sliding door is suitable for:

• Openings up to 25.5m² overall (or 36m² in the minimal windows^® 4+ system)
• Openings where you want to maximise a centralised view
• In doorways where you want to maximise useable opening space (have as big a useable door opening as possible)

There is both a two-pane minimal window^® and a three-pane on show at the IQ Glass showroom in Amersham. This space is the largest architectural glazing showroom in the UK and the sole minimal windows^® show location in the UK. Make sure you contact IQ Glass to book your appointment to visit and view.

For any questions regarding the minimal windows^® or minimal windows^® 4+ systems please let us know and we will be happy to offer advice and guidance for specification.