Slim Sightline Bifold Doors: How Narrow Can a Bifold Go?

Every bifold door has frames where the panels meet, and the width of those frames decides how much of the view you actually see. Slim sightline bifolds are designed to make those frames as narrow as possible, so a closed set reads almost as one continuous wall of glass.

This guide explains what a sightline is, why brand figures are easy to compare unfairly, and how narrow the slim bifolds we fit actually go.

What Is a Sightline?

A sightline is the width of frame you see between two panes of glass. On a bifold, the important ones are where two panels hinge together and where the two lead panels meet when the door is closed. Because a bifold folds, it has more of these meeting points than a sliding door of the same width, which is why sightlines matter more on bifolds than on almost any other door.

Why Brand Figures Are Hard to Compare

Manufacturers do not all measure the same thing. Some quote the width of a single sash (the frame around each glass panel), some the meeting point between two sashes, and some the full glass-to-glass distance. Origin's model names are a good example: the 36, 49 and 72 in OB-36+, OB-49 and OB-72 are the sash widths, while the glass-to-glass sightlines at the hinge are 84 mm, 110 mm and 154 mm.

The fair way to compare is always glass to glass: how much frame sits between two panes when you look at the closed door.

How Narrow Do Slim Bifolds Go?

These are the published sightlines for the slim bifolds we supply and install. Each manufacturer measures at a different point, shown in each row, so treat the comparison as a guide:

| System | Published sightline | Where it is measured | |---|---|---| | Origin OB-36+ | 84 mm | Between panes at the hinge | | Schuco AS FD 75 | 90 mm | Meeting point between panels | | Cortizo Bi-fold Plus Door | 110 mm | Reduced central junction | | Origin OB-49 | 110 mm (134 mm at the lock stile) | Between panes at the hinge | | Origin OB-72 | 154 mm (164 mm at the lock stile) | Between panes at the hinge |

The Origin OB-36+ is Origin's slimmest bifold and among the slimmest we fit, with just 84 mm of frame between panes at the hinge.

What You Give Up for a Slimmer Frame

Very little, on the best systems. The OB-36+ still takes panels up to 1,200 mm wide and 2,846 mm tall, up to 14 panels and 15,000 mm across with track connectors. With triple glazing it reaches a whole-door U-value (the measure of heat loss, where lower is better) of 0.78 W/m²K, and it is tested to PAS 24:2022, the current edition of the UK security standard.

What changes between systems is mostly appearance and specification detail: frame depth, the threshold options, bead style and the finishes available. Where an opening is very exposed, or where you want woodgrain finishes, a broader frame such as the Origin OB-72 can be the better choice.

The Steel Look: Soho Style

Slim frames suit the steel-look style many clients ask for in kitchen extensions. Origin's OB-36+ is available in its Soho style, which adds a traditional lock block and integral glazing divides so a slim aluminium bifold reads like a steel-framed door. Gallery and Georgian are Origin's alternative styles for the same door.

Bifold or Sliding for Slim Frames?

If the slimmest possible frame is the only priority, a sliding door usually wins, because it has fewer meeting points. The Origin OS-29+ sliding door has a 29 mm interlock, the frame where its sliding panels meet. A bifold wins when you want the whole opening clear, with the panels stacked neatly to one side. Our guide to bifold vs sliding vs French doors covers the choice in full.

Frequently Asked Questions

Which Origin bifold has the slimmest frames?

The Origin OB-36+, with an 84 mm glass-to-glass sightline at the hinge and a 36 mm sash. It is Origin's slimmest bifold and among the slimmest we supply and install.

Is a 36 mm bifold really 36 mm between the glass?

No. On the Origin OB-36+ the 36 mm figure is the sash width. The glass-to-glass sightline at the hinge is 84 mm, which is still very slim for a bifold.

Are slim bifold doors less secure?

Not on the systems we fit. The Origin OB-36+ is tested to PAS 24:2022, the current edition of the UK security standard, with a multi-point lock and a 3-Star Diamond cylinder as standard.

How energy efficient is a slim bifold?

The Origin OB-36+ reaches a whole-door U-value of 0.78 W/m²K with triple glazing, and 1.4 W/m²K with a standard double-glazed unit, which meets Part L, the energy-efficiency part of the Building Regulations, for replacement doors.

How big can a slim bifold be?

On the Origin OB-36+, each panel can be up to 1,200 mm wide and 2,846 mm tall, and a set can run to 14 panels and up to 15,000 mm wide with track connectors.

Next Steps

See the full specification and comparison table on our Origin bifold doors page, or compare brands in our Cortizo vs Origin bifold doors guide. When you are ready, request a free quote or call 0800 861 1450.