The full opening, without compromise. Folding doors in steel and aluminium.

A sliding door moves one or more panels parallel to the wall — the opening is clear but the panels remain visible, either stacked against the wall or recessed into a pocket. A folding door stacks its panels concertina-style to one or both sides, clearing the full width of the opening. If the design intent is a complete connection between interior and exterior — with no panel in the way — folding is the solution. If the opening allows for partial clearance or the panels can recess, sliding may be equally effective. We advise on which is right for each specific opening.

Steel is preferred for interior applications and where the slimmest possible profile is a design priority. For exterior folding doors on the Costa del Sol — where thermal performance, weather resistance and longevity in a coastal climate matter — aluminium with a thermal break is typically the correct specification. The MHB SL30-ISO® system uses thermally broken steel for exterior applications, which gives the slim profile of steel with the performance requirements of an exterior system. The material is determined by where the door sits and what the project requires — not by preference alone.

MHB is a Dutch manufacturer of precision steel door and window systems, established in 1667. Their folding door range uses the patented SL30-ISO® thermally broken steel profile — engineered specifically for exterior applications where thermal performance and weather resistance are non-negotiable. The system is water-tight to Class 4A and has been tested to Class 9A (600Pa), with thermal transmittance of up to Uw 0.73 W/m²K. Royal Design Marbella is the MHB partner on the Costa del Sol — we manage the full process from specification and supply through to site coordination and handover.

The MHB system is available in 3 or 5 sash configurations. For bespoke interior systems we develop the panel count around the specific opening — 2, 3, 4 or more panels depending on the span and the stacking direction required. More panels across a wider opening means more hinge load, a more demanding track specification and a more complex installation. All of this is resolved at the design stage, before fabrication begins. The practical limit in each case is the structural conditions of the opening and the weight of the glass specification.

This is the most common application for folding doors on the Costa del Sol — connecting a living or dining space entirely to a terrace, pool area or garden. The climate makes this a practical as well as a design decision: when the doors are fully open, the indoor-outdoor threshold disappears. For this application, the system needs to be specified for exterior use: certified thermal performance, appropriate weather sealing and hardware rated for coastal exposure. We have installed MHB exterior folding systems across projects in Marbella, Benahavís, Estepona and Sotogrande.

For interior folding systems, clear toughened glass is standard. Laminated, satin, tinted or acoustic-grade glass are available where the project requires them. For exterior MHB systems, thermally insulated double-glazed units with a thermal break are standard. Glass weight directly affects the hinge and track specification — a heavier glass unit requires a more robust system throughout. The glass specification is confirmed at the technical design stage and is treated as part of the engineering, not a finish choice made at the end.

For bespoke interior steel systems, matte black, dark anthracite and brushed steel are standard, with bespoke RAL matching available for projects where the frame needs to align with a specific material palette. For MHB exterior systems, the full MHB finish range is available — including standard and premium powder coat colours and precious metal finishes such as bronze. Finish is confirmed at the specification stage and applied consistently across frame, track and hardware throughout the system.

For bespoke interior systems and Royal Glassea glazing solutions, our own team manages the installation directly. For MHB exterior systems, installation is carried out by MHB — Royal Design Marbella coordinates and manages the full process on site, from access planning and contractor coordination through to commissioning and handover. In both cases, structural conditions, floor finishes and ceiling details are assessed before fabrication begins. We do not consider a project complete until the system operates exactly as it was designed to.

Working with architects and interior designers is where we spend most of our time. We work from their drawings, respond to technical questions with the detail they need, and flag any issues during the specification stage rather than on site. We do not need to be in every conversation — but we keep the right people informed at every stage. If a folding door system is specified in the project, we develop the technical detail in coordination with the design team and manage our scope without adding complexity to the programme.

The more specific you can be, the faster and more useful our response will be. Ideally: architectural drawings or a dimensioned sketch of the opening, the project location, whether the application is interior or exterior, and a brief description of what you are trying to achieve. If you have a finish preference or a glass specification in mind, include it. If you do not have drawings yet, a description of the opening dimensions, the project type and the design intent is enough to start a useful conversation. Send us what you have — we will take it from there.