Bi-Fold Doors

Commercial bi-fold door systems — sometimes called bifold or folding-sliding doors — are increasingly specified for retail, hospitality, and leisure premises where the ability to open up an entire frontage or elevation creates a fundamentally different trading proposition. A café that can open its complete street-facing wall on a warm day, or a showroom that can create a seamless transition between indoor display and an external forecourt, gains a competitive advantage that a conventional hinged or sliding arrangement simply cannot replicate.

Sigma Shop Fronts designs and installs commercial aluminium bi-fold systems to suit openings from 2 m to over 12 m in width. Our systems are sourced from fabricators whose products are independently tested and certified to the performance standards that commercial applications demand.

How Commercial Bi-Fold Systems Work

A bi-fold door system consists of a series of individual door panels — typically between two and eight per run — connected by hinges and suspended from a top-hung track or supported by a bottom-running track. When opening, the panels fold against each other accordion-fashion and stack compactly to one or both sides of the opening, creating the maximum possible clear aperture.

Top-hung systems are preferred for commercial use: because the track carries the panel weight, the floor threshold can be a low-profile weather seal rather than a structural bottom track, minimising the trip hazard and improving DDA compliance. Bottom-running systems are used where the header structure cannot carry the suspended load, but they require a more substantial threshold detail.

The stacking configuration — whether panels fold to the left, to the right, or split to both sides — is determined by the operational requirements and the available stacking space. Traffic-door options (a separate hinged panel within the bi-fold run that operates independently) allow pedestrian access without opening the full system.

Weather Performance and Testing

Commercial bi-fold doors are exposed to the full range of UK weather conditions, including driving rain, wind loads, and thermal cycling. The relevant performance standard is BS 6375, which covers air permeability, watertightness, and wind resistance for opening building elements. For commercial premises facing exposed street elevations, we specify systems tested to the mid-range or upper categories of BS 6375 — typically Class 3 or 4 for watertightness and Category B or C for wind resistance — rather than the lower-category systems marketed primarily at the residential sector.

Thermal performance is addressed through thermally broken frame profiles. Unlike most residential bi-fold systems, which use a standard aluminium section, our commercial-grade systems incorporate a continuous polyamide thermal break throughout the frame and sill, delivering a complete door assembly U-value compliant with Building Regulations Part L for non-domestic buildings.

Structural Requirements

Opening up a large section of an existing building elevation for a bi-fold installation almost always involves structural work. The removal of masonry or the widening of an existing opening requires a structural engineer's design for the replacement lintel or beam — typically a steel universal beam or a reinforced concrete boot lintel — sized to carry the loads above, including wind uplift and the weight of the new door system.

We coordinate this structural work as part of our project management service, and where Building Regulations approval is required for the structural alteration, we manage the application through an Approved Inspector or local authority building control.

Glazing and Security

Bi-fold door panels are typically glazed with double-glazed units incorporating toughened outer and inner panes. For enhanced security, laminated inner panes to BS EN ISO 12543 (laminated glass) can be specified; these resist the smash-and-grab attack that a toughened monolithic pane is vulnerable to after initial fracture.

Locking is provided at multiple points along each panel. The outermost panel — the one that closes against the threshold and jamb when the system is shut — carries the primary locking hardware, typically a multi-point espagnolette or shoot-bolt system engaging the frame at the head, sill, and strike side. The folded stack of inner panels is secured against the outer panel by secondary locks.

For overnight security in high-footfall or high-risk locations, bi-fold systems can be combined with a roller shutter in the same structural opening, with the shutter housing concealed within the header detail above the bi-fold frame.