When a project calls for a large glazed opening, aluminium bi-fold doors and sliding doors are usually the two systems being considered.
Both can create large areas of glass, improve natural light and connect internal and external spaces. But they achieve it in very different ways.
For installers, builders and developers, the decision should go beyond appearance. Opening size, panel dimensions, sightlines, structural requirements, access, operation and budget all need to be considered.
Here’s where each system works best.
Bi-Fold Doors: Maximum Opening
The biggest advantage of a bi-fold door is simple: it can open up almost the entire aperture.
Individual leaves fold and stack together at one or both ends of the opening. When fully opened, there is very little separating the internal and external spaces.
This makes bi-folds particularly effective for:
- Extensions opening onto patios or gardens
- Kitchen and dining spaces
- Entertaining areas
- Projects where maximum clear access is important
- Openings where the customer wants the doors completely out of the way
Arkay’s aluminium bi-fold options can accommodate substantial openings. IconiK, for example, can be configured with up to seven leaves, with individual panels up to 1,200mm wide and 3,000mm high, subject to configuration and project requirements.
The Trade-Off: More Aluminium When Closed
The folding mechanism requires multiple individual door leaves.
That means more vertical aluminium across the opening when the doors are closed compared with a slimline sliding system. Even Arkay’s slimmest bi-fold sightline is around 87mm, compared with 20mm on the slimmest sliding systems.
On a project where the doors will remain closed for much of the year, that distinction matters. The customer gets an exceptional opening when the bi-fold is open, but more visible frame when it is closed.
Traffic-door access also needs to be considered. With an even number of bi-fold panels, a dedicated traffic door cannot be incorporated, which can make everyday access in and out of the property less convenient.
Think of bi-folds as prioritising the opening.
Where Bi-Folds Still Have the Advantage
Slim sliding doors may dominate when the brief is “as much glass as possible”, but bi-folds remain difficult to beat when physical access through the opening is the priority.
Imagine a kitchen extension opening onto a terrace.
With a slider, part of the glazed elevation remains in position when the door is open.
With a bi-fold, the leaves can stack away to create a much wider opening.
For customers who regularly entertain, want a strong indoor-outdoor connection or simply want the ability to open an elevation up during summer, that can be more valuable than achieving the smallest possible sightline.
Sliding Doors: Maximum Glass
Sliding doors approach the same aperture differently.
Instead of several smaller leaves folding together, large glazed panels slide horizontally across one another. This allows the system to use fewer, significantly larger panes of glass.
The result is less interruption to the view.
Arkay’s sliding range demonstrates how far this can be taken. EdgeGlide+ uses a 35mm interlock and accommodates panels up to 2,200mm wide by 2,600mm to 3m heigh, while InfiniGlide 3 offers a 20mm interlock for a more minimal appearance.
This makes sliding doors particularly suited to:
- Contemporary extensions
- Large rear elevations
- Architect-led properties
- Projects overlooking gardens or views
- Customers prioritising glass and natural light
The Trade-Off: The Opening Is Different
A conventional sliding system doesn’t normally provide the same completely clear opening as a bi-fold.
Panels slide behind one another rather than folding away.
That doesn’t make the system less practical. It simply creates a different result.
Think of sliding doors as prioritising the view.
Where Sliding Doors Really Come Into Their Own
Modern aluminium systems have pushed sliding doors far beyond the traditional patio door.
Larger panel sizes create impressive floor-to-ceiling glazing, while increasingly slim interlocks reduce the amount of visible aluminium.
There are also opportunities to conceal more of the frame within the building structure. GLIDE21 uses a hidden sash and a concealable outer frame, allowing the system to achieve a much more integrated, minimal appearance.
For a high-end project, this can fundamentally change the architecture of an elevation.
Instead of the door appearing as a separate product fitted into an opening, the glazing can become part of the architectural design itself.
Don’t Specify on Sightlines Alone
Sightline figures are useful, but they shouldn’t dictate the specification by themselves.
Installers also need to consider:
Panel size and weight. Larger panes create impressive elevations, but glass weight and handling need to be considered.
Structural requirements. Depending on the property’s location, large openings can introduce deflection and wind-loading considerations that need to be addressed at specification stage.
Threshold requirements. Flush and low-threshold details can dramatically improve the finished result, but drainage, weather performance and surrounding construction must be properly considered.
Configuration. A three-panel slider, six-leaf bi-fold and two-panel slider will all behave very differently even if they occupy a similar aperture.
Security and thermal performance. These need to be assessed against the project’s requirements rather than assuming one door type automatically performs better than another.
The best door is therefore not simply the system with the smallest number on the brochure.
It is the system that works with the building.
Bi-Fold or Sliding Door?
There isn’t a universal winner.
Choose bi-fold doors when the priority is:
Maximum opening → flexible access → strong indoor/outdoor connection.
Choose sliding doors when the priority is:
Maximum glass → minimal sightlines → uninterrupted views.
And on larger projects, there is no reason the two can’t work together. A main living space might use large slimline sliding doors to maximise the view, while another elevation uses bi-folds where completely opening the space is more important.
The possibilities come from specifying each opening around how it will actually be used.
Get the Specification Right Before Ordering
For trade customers, the important decision isn’t simply bi-fold or slider?
It’s which system, configuration and specification will deliver the required result without creating unnecessary complications on site.
Arkay Windows manufactures a range of aluminium bi-fold and sliding door systems for trade installers, builders and developers, including UniFold HI, ICONIK, EdgeGlide+, InfiniGlide 3 and GLIDE21. Arkay also provides technical support to help customers select products appropriate to different project requirements.
Have an opening you’re trying to specify? Speak to Arkay about the dimensions, project requirements and desired finish, and we can help identify the right aluminium door system before you quote the job.