Fluid Folding Door: Slim Bi-Fold Doors, Flush Threshold

Bi-fold doors carry more frame than sliding doors, so with aluminium bifold doors every leaf needs its own stile and face width is the number that decides whether a folding door reads as glazing or as a row of frames. At 110mm this system sits at the slim end of the category, and those slim sightlines improve the look of the door while aluminium’s high strength-to-weight ratio helps achieve narrower frames. Where an uninterrupted pane matters more than a fully opening wall, the Fluid X Sliding Door is worth considering.

The bottom track is fully weathered and flush, so floor levels run continuously between inside and out with no trip hazard and no rebated upstand. For external bifold doors, the panels can be configured to open inward or outward and stack on either side. A primary access leaf or traffic door also gives easy access without folding the full set back. That is unusual: most flush thresholds achieve the level finish by giving up weather performance. For internal transitions, such as between a house and a conservatory, a non-weathered low threshold recesses into the floor instead.

A 45mm thermal break and 48mm glazing capacity for high-performance double glazed units give a whole-door U-value of 0.8 W/m²K — one of the strongest figure across the Fluid Glass opening systems. That whole-door figure points to low u values and strong thermal performance, with modern aluminium bi-fold doors with thermally broken frames typically reaching around 0.9–1.6 W/m²K. Thermally broken frames and high-performance glazing also improve energy efficiency and can help reduce energy costs year-round. Acoustic insulation reaches 41dB. Weather performance is Class 4 air permeability, Class E750 water tightness and Class C3 wind resistance.

The system runs to 14 sashes on these bifold doors, so a full elevation can be folded back, and a 90° opening corner removes the post where two runs meet. For more typical residential aluminium bifolds, choose from two panels up to 7 panels, with how many panels depending on the opening and whether you want an even or odd arrangement; aluminium bi fold doors can create openings up to 16.4m wide. Leaves run to 3m high by 1.2m wide at weights up to 120kg. Where the priority is opening the entire wall rather than a clean line when closed, this is the system that does it.

Operation is carried by a double bearing system with a gimbal stabiliser, which keeps leaves running true so they operate smoothly as they fold and resists the racking that makes older bi folding doors stiff over time. Wheel rollers carry the leaf weight. This is the part of a folding door that fails first, and it is where the German engineering in this system is spent.

Our aluminium bi-fold door achieves Class C3 wind resistance, helping it remain stable and secure in windy conditions. Its security features include PAS 24 certification, multi point locking systems, anti-lift blocks, 3-star cylinder locks, and reinforced glass for enhanced protection. It's a reassuring performance rating for a door designed to open up your space without compromising its protection from the elements.

The flush threshold only works if the floor build-up and drainage are planned around it, which makes this an external bifold design-stage decision rather than a supply item. We design, engineer, fabricate and install in-house, and installation quality affects long-term performance. Customisation includes hardware options and glazing options. See the Fluid Folding Door at Berkeley Road, Courthope and OMA Restaurant, or operate one at our Watford showroom.

Architects — where the brief calls for the entire opening to be cleared, and the threshold has to finish level with the internal floor.

Homeowners — for a garden elevation you want to open completely in summer rather than partly at any time.

Developers — where a folding system has to repeat across plots with a consistent threshold detail.