Curved Staircase UK: Dual Matched Pair for Felixstowe Residence

The Challenge

Producing a single curved staircase is already a precision exercise. Producing two curved staircases that must read as a matched pair doubles the geometric complexity and introduces a category of error that does not exist in single-stair projects: asymmetry between the runs. If Stair A and Stair B differ in radius by even 10 mm, or if the rise-and-going geometry drifts by half a degree of pitch, the mismatch becomes visible the moment both stairs are viewed simultaneously — which, in this Felixstowe residence, is from every major vantage point in the ground-floor living area.

The UK Building Regulations impose dimensional constraints that must be identical across both stairs to avoid creating a trip hazard or failing inspection. Approved Document K requires consistent rise and going within each flight, but when two stairs serve the same level change in the same visual field, good practice demands that both stairs share identical geometry — same rise (maximum 220 mm for domestic), same going (minimum 220 mm), same pitch angle, and same number of treads. Any deviation between stairs A and B would create an inconsistency that experienced Building Control Officers would likely question.

The mirrored configuration added a further constraint: Stair A curves to the left and Stair B curves to the right (or vice versa), meaning they share the same radius but are fabricated as mirror images. This sounds simple, but in practice it means the glass panel templates, spigot positions, and handrail segments for Stair B cannot simply be duplicated from Stair A — they must be mirrored, which requires a separate set of fabrication jigs and separate CNC programs for each run. Any shortcut (such as using the same jigs and flipping components) risks introducing subtle errors at the glass panel breaks and handrail splice points.

Project Gallery

The hero image shows one of the two curved runs from the ground-floor perspective. The visual test for a dual-staircase project is simple: can you look at one stair and then the other without sensing that something is different? If the radii, glass panel breaks, handrail heights, and finish tones are correctly matched, the eye accepts both stairs as parts of the same design. If any of those elements are off, the pair feels like two separate projects installed in the same room. Our curved staircase systems use a shared parametric model for paired installations — both stairs are generated from the same master geometry file, with a mirror operation applied to the second run, ensuring that every dimensional relationship is mathematically identical.

The detail images below show the glass panel alignment, handrail curvature, and stringer finish on both runs. Compare the panel break positions between Stair A and Stair B in the gallery — they occur at corresponding tread positions on each run, creating a visual rhythm that reinforces the paired relationship.

Our Solution

Shared Parametric Geometry

Both staircases were designed from a single parametric model in our 3D engineering software. Stair A was designed first as the master geometry, then a mirror operation generated Stair B. This approach ensures mathematical identity between the two runs — the radii, rise/going ratios, tread positions, and panel break locations are not “approximately equal” but numerically identical (mirrored about the center axis). The parametric model then generated separate fabrication outputs for each stair:

• Stringer rolling programs: CNC bending instructions for each stringer section, with Stair B segments rolled in the opposite direction to Stair A.
• Glass panel templates: Individual DXF cutting files for each panel, accounting for the trapezoidal shape that results from the curved geometry. Stair B panels are mirror-image versions of the corresponding Stair A panels — same dimensions, opposite hand.
• Handrail segments: Pre-curved stainless steel tube sections, rolled to match the stringer radius. Again, Stair B segments are mirrored — the curve direction reverses, but the radius and sweep angles are identical.

Material and Finish Consistency

• Steel stringers (S275JR): Both stair structures were fabricated from the same steel batch to ensure consistent material properties and weld color. They were powder-coated simultaneously in the same batch run (RAL 9005, 80 μm DFT) to eliminate the colour variation that can occur between separate coating batches.
• 10mm tempered glass: All panels for both stairs were cut from the same glass production lot (same batch of float glass, same tempering run) to ensure identical optical clarity and edge color. Glass from different lots can exhibit visible differences in the green tint when viewed edge-on — a detail that becomes obvious when two stairs face each other across a room.
• 304 stainless handrail: Both handrails were brushed in the same session using the same 320-grit belt, running in the same direction relative to the handrail curvature. This produces identical brush-line orientation on both runs — a detail that would be nearly impossible to achieve if the handrails were finished at different times.

Guard Compliance

Both stairs comply with Approved Document K: 900 mm guard height on the stair runs, stepping to 1,100 mm at the landings. Glass infill prevents passage of a 100 mm sphere. The guard system resists the BS 6180 domestic barrier load of 0.36 kN/m horizontal at the top rail. Both stairs have identical handrail profiles (42.4 mm CHS) providing continuous graspable surfaces along the full run.

Delivery & Installation

A dual-staircase shipment is effectively two full staircase packages in one container. The critical logistics challenge was preventing component mixing — if a Stair B stringer section were mistakenly installed in the Stair A position, the mirrored curve would be immediately obvious and require complete disassembly to correct.

Colour-Coded Packaging System

• Stair A components: All crates, labels, and component tags in BLUE. Blue stickers on each stringer section, glass panel, handrail segment, and hardware set.
• Stair B components: All crates, labels, and component tags in RED. Red stickers on each corresponding component.
• Shared hardware: Anchor bolts, gaskets, and other non-handed components were packed in WHITE-labeled cartons to indicate they could be used on either stair.

Within each colour-coded set, components were further numbered in installation sequence (A-01, A-02… B-01, B-02…) so the site team could install each stair in order without consulting drawings for every piece. The drawing package included a side-by-side erection diagram showing both stairs with their colour codes, plus a critical warning callout: “Do not interchange BLUE and RED components — mirror geometry will not fit.”

Installation followed a parallel sequence: both stairs were erected simultaneously by a 4-person crew (2 per stair), with each pair following the same step-by-step build-up. This parallel approach ensures that both stairs reach the same construction stage at the same time, allowing visual comparison at each phase to catch any discrepancy before the next layer of components is added. For multi-stair residential projects, our stair and railing coordination reference includes dual-stair installation protocols and the colour-coded component management system that prevents cross-installation errors.

The Result

The completed installation delivers what a dual-staircase project must achieve above all else: symmetry that feels natural. Standing in the center of the ground-floor living area, both stairs sweep upward in mirrored curves with identical glass panel rhythms, matching handrail profiles, and indistinguishable finish tones. The eye accepts them as a paired architectural feature — which is only possible because every dimension, material batch, and finish operation was controlled for consistency throughout the fabrication and installation process.

Both stairs comply with Approved Document K: identical rise and going geometry (verifiable by Building Control as consistent between runs), 900/1,100 mm guard heights at stair and landing levels respectively, and BS 6180-compliant barrier load resistance. The glass panels maintain consistent spacing and edge alignment on both runs, and the stainless handrails provide identical graspable profiles throughout.

The Felixstowe project demonstrates a capability that most staircase suppliers avoid: producing matched pairs with factory-controlled consistency. Single-stair projects can absorb minor variations because there is no adjacent reference point. Paired stairs expose every inconsistency immediately — which makes the fabrication controls, batch management, and colour-coded logistics system not optional refinements but essential engineering requirements for this category of project.

Related Guides & Resources

• 10 Costly Staircase & Railing Mistakes to Avoid (2026)
• How to Choose the Right Staircase: 2026 Decision Guide
• Powder Coat vs Brushed Stainless Glass Railing 2026
• Contact Double Building Materials