Corner Bifold Doors and Glass-to-Glass Corners Explained

1 day ago

4 min read

Dark aluminium bifold doors folded back at the corner of a kitchen-dining extension, opening onto a paved patio

Corner bifold doors are two sets of folding doors that meet at the corner of a room with no fixed post between them, so when both sets are folded back the corner simply disappears and the room opens on two sides at once. The trick is structural: the roof or floor above has to be carried by a steel goalpost or a cantilevered frame, because the corner where a wall would normally take the load is now thin air.

How does a corner bifold door work without a post?

Two things happen at the corner. First, the structure above is redesigned so nothing rests on the corner itself. Typically a steel frame is formed around the two openings, with a column set back from the corner inside each wall, and a beam spanning across the top of both openings and meeting at the corner. The corner is then a joint between two beams, carried by the columns either side, and the doors sit in the openings beneath.

Second, the two door sets are made so their meeting stiles form the corner. On a bifold, one set folds and stacks to the left, the other to the right, and when closed the two end panes meet at the corner with a slim aluminium post that is part of the doors, not the building. It locks in place when the doors are shut and folds away with the leaves when they open. The post is the price of the bifold: when the doors are closed, there is a frame at the corner.

What is a glass-to-glass corner?

A glass-to-glass corner removes even that. On a fixed or sliding glazing system the two panes meet at the corner with a structural silicone joint and no frame at all, so the view runs unbroken around the corner. Our ultra-slim frame sliding doors can be specified with glass-to-glass corners, with panes bonded to ultra-slim aluminium frames so that the doors are 99 per cent glass, and with motors on larger panels so a corner pane of several square metres still glides open. When both corner panes slide away, the corner opens just as a bifold corner does.

Frameless sliding glass walls meeting at a glass-to-glass corner of a living space onto a lit pool terrace at dusk

This is the difference in one sentence: a corner bifold gives you an open corner with a post when closed; a glass-to-glass sliding corner gives you an open corner with nothing when closed.

Corner bifold or corner sliding doors?

Bifolds open the full width of both walls, so if the brief is a summer room that becomes a terrace, corner bifolds do it and sliders, which always keep a pane in the line, do not. Sliding doors give the better view the rest of the year and cope better with very large panes and exposed elevations. Most corners we are asked for are kitchens or living spaces where the view is enjoyed daily and the full opening used a handful of times a year, so our first suggestion is usually a sliding corner. Our guide to aluminium bifold doors covers the bifold specification.

What does the corner ask of the building?

A structural engineer designs the goalpost or cantilever, and the calculations go with the building regulations application. On an existing house the corner is propped while the steel goes in, and the foundations at the two column positions are checked and often enlarged, because loads spread along two walls now arrive at two points. The beams must allow for deflection so the doors never bind, and a flush threshold needs its drainage channel mitred round the corner.

Which rooms suit a corner opening?

A kitchen-diner in the rear corner of a house, with the garden on two sides, is the classic case. A living room that turns a corner towards a view, a garden room that sits diagonally in the plot, and a first-floor room opening onto a corner terrace all work, and on a glass box extension the corner is often the whole architectural idea. Orientation matters: a corner with south and west glazing will need solar control glass or external shade, because two glazed walls collect a great deal of afternoon sun.

What about security and weather at the corner?

On a bifold corner the post locks the two sets together with shoot bolts, and each set has multi-point locking; on a sliding corner the panes lock to the outer frames. Our bifolding and sliding doors are measured after the steel is in, which is the only way to make a corner seal.

Corner bifold door questions, answered

Do corner doors need planning permission?

The doors themselves do not. In England, forming a new corner opening is usually permitted development, but it always needs building regulations approval because of the structural work. A listed building needs listed building consent, and in a conservation area rights are more restricted, so check first.

Are corner bifold doors expensive?

The doors are priced like any bifold of the same width. The extra cost is the steel, the engineer's design and the more complex installation, which vary with the house. Our guide to bifold doors cost explains what drives the price of the doors.

Can a corner opening be motorised?

On an ultra-slim sliding corner, yes. Large or triple-glazed corner panes are motorised so they open at a touch, and the motor can be tied into electric locking.