Here, Paul Higgins of TuffX explores the key reasons for self-builders to specify bi-fold doors, from slimline sightlines to revolutionary heated solutions.

Bi-fold external doors offer the ideal balance of practicality, aesthetics, and functionality, whether used to create unobstructed garden views in a new build, or add a contemporary touch to a period property renovation. Expert design and specification of the bi-folds are crucial to ensure the view beyond the windows is maximised. Depending on the width of the opening, opting for wider individual doors will automatically reduce the number of mullions, for better sightlines. Slimline frames allow the panel/glazing to be maximised with fewer panels per opening to flood the internal space with even more natural light. 

Generally, the minimum recommended width for a bi-fold design would be 140 mm (4.7 ft), allowing for two panels – a configuration that would benefit from a slimline sightline solution. Then, upwards, there’s no limit to the number of doors; there would be increased requirements for how many tracks must be joined together during installation.

While not strictly ‘bi-fold’, as they’re usually a slide-and-fold system, fully frameless options further minimise interruption of the vertical sightlines to create a ‘wall of glass’ effect visually.

Revolutionary heated glass for bi-folds

Taking bi-folds to the next multifunctional level, it’s now possible to specify heated glass into bi-folding doors, enabling both natural daylight and thermal comfort to be enhanced simultaneously. A sealed unit can be combined with an intelligent, invisible conductive coating that is electrically heated to convert electric power into radiant heat. The units are thermostatically controlled, creating ambient temperatures ideal for aluminium bi-folding door systems.

The glass surface temperatures reach 35-40°C and are controlled via a wall-mounted thermostat, allowing the unit to become the primary heat source, freeing up wall space where radiators would be, and enhancing interior layout opportunities. The average hourly cost of around 9p per bi-fold door means that for example, a three-door bi-fold configuration running for five hours per day will cost around £1.35 (based on an electricity cost of 25p/kWh). The installation costs are lower than electric underfloor heating or traditional radiators, making it a more budget-friendly option.

Heated glass also dramatically reduces condensation, preserving uninterrupted views and potentially contributing to a healthier indoor environment. Plus, no ongoing maintenance is required, providing a ‘hassle-free’ heating solution compared to systems that need regular servicing.

Cutting (out) corners

For some projects, a cornerless bi-fold configuration will truly open up a property’s interior to the outside by installing two sets of doors at either 90° or 135° to each other to create a seamless transition. Aside from the specification of the doors themselves, whether they are slimline, frameless or incorporate heated glass, another key consideration with a corner-less design is the structural implications.

When removing a corner of an existing building or incorporating a corner-less design into a new build or extension, there are a couple of ways to achieve the structural requirements to ensure the weight of the building’s upper floors and roof is supported. A structural engineer may advise installing either a corner post potentially together with RSJs on either side of the opening or a cantilever roof. 

Both options will provide reassurance that the building is structurally sound and ensure there isn’t too much weight on the door frame once in place, as this could prevent the doors from sliding and functioning correctly. Once the opening is structurally sound, the bi-fold door design itself and, notably, the costs are no different from specifying doors for any other opening.

Achieving the ideal balance

Whichever product and design specification works best for the project, it’s important to take a broader view of how the bi-folds work with surrounding spaces. When choosing whether to incorporate a traffic door for easy access to the garden or which direction the doors should slide and gather into, consider how this will look and function outside. For example, when open, will the doors be stacked in the middle of a patio creating layout issues, or if they fold inside, will it prevent furniture from being placed by the window? 

Walking through and planning these aspects at the design stage is critical to ensuring the finished installation provides the perfect balance of aesthetics, functionality, flexibility and, with heated glass, thermal comfort.

Paul Higgins is commercial director at TuffX