Bridging the divide: a question of choice

David Clarke of IDSystems looks at the options for specifiers when it comes to choosing glazed doors to bring the outside in

Bridging the divide between indoors and outdoors is one of the main reasons homeowners seek to employ ‘open plan’ design in their properties.

To address this demand, architects are turning their attention to different types of glazing to visually unlock the space and maximise natural light. In residential developments, the choice open to architects would most often come down to picking between bi-fold doors and sliding doors.

While each type has its pros and cons, specifiers must take into account various factors before deciding which one is right for their project.

Bi-fold doors

These doors work perfectly whether installed in a small urban courtyard to flood the property with light or in a clifftop rural location to reveal the surroundings, for example. Popular on the continent for decades, the UK bi-fold door market has only taken off in the last five to 10 years.

Available in a variety of materials including aluminium, timber and composite, the big advantage of the bi-fold door is its ability to completely open up a space, seamlessly connecting the outside and inside without any physical partition being present. With a maximum panel width of around 1100 mm, bi-fold doors are perfectly suited for smaller openings that can incorporate a single access door. As part of a system with an odd number of leafs, the doors provide a combination of practicality when closed and visual appeal once open.

Bi-folds with a flush track are best suited for sheltered locations where the track lies within the floor, enabling a level threshold inside and out. Alternatively, there are weathered tracks offering a small step down that creates an effective weather seal, best suited for more exposed locations.

One thing however would not escape those with an eye for detail – at least some part of the door frame will remain visible. For example with the Sunflex SF55 aluminium system, the sightlines are 115 mm in width – meaning on a 5 metre opening 46 cm of frame would be visible.

Sliding doors

These systems have come a long way since early aluminium sliding doors became commonplace in the late 1970s.
Unrecognisable from their predecessors, the modern systems run smoothly for ease of use while their narrow frames allow for the creation of visually attractive projects. Aluminium is the material used for the majority of sliding doors sold in the UK, but timber options, which can provide wider panels with glass sizes of up to 3,000 mm wide, are also available.

Moreover, timber systems require a minimal amount of vertical frame. Sliding doors’ main advantage is their narrower profile – with a higher proportion of glass to frame, these systems offer a year-round solution for maximising views or natural light.

The trade-off though is that unlike bifold doors, sliding doors do not create a complete opening, with one panel of glass usually visible at all times, unless the system is slid into a pocket. Typical configurations provide a half, two-thirds and three quarters opening, and are best suited for large openings.


While inherently different, bi-fold and sliding door systems share many attributes in terms of performance, price and customisable options. Bi-fold doors tend to be priced per panel and for German-engineered aluminium systems customers can expect to pay from around £1,200 per double-glazed panel.

Sliding doors are usually priced per linear metre and the starting cost of a high quality aluminium system is around £1,200 per metre. To enhance thermal performance, a system should meet Part L of Building Regulations and double-glazed bi-fold and sliding doors can provide U-values around 1.6 W/m²K – triple glazed versions are capable of around 1.3-1.4 W/m²K.

Highly thermally broken aluminium bi-fold doors can achieve values as low as 0.9 W/m²K. Both types of doors can be customised in any RAL colour and finish in aluminium and timber options, with a range of handles and hardware. Moreover, both can be used in conjunction with moveable corner posts to create completely open corners.

In conclusion

There is no right or wrong answer when choosing between bi-fold and sliding doors for an open plan living space. The key factors come down to location, the amount of time they are likely to be opened and the size of the opening.

As a general rule, sliding doors are more apt for bigger openings while bi-fold systems are typically better suited for smaller ones.

David Clarke is marketing coordinator for IDSystems