Metal Balustrade Calculator — Posts, Handrail & Infill Bars

BS 6180 and Approved Document K require that a 100mm diameter sphere cannot pass through any opening in a balustrade where children under 5 may be present (residential, schools, public buildings). This means the clear gap between vertical bars must be less than 100mm. BS 6180 requires this to hold allowing for deflection of the bars under load, so in practice the clear gap is set comfortably under 100mm — this calculator targets around 88-90mm clear to keep a margin. The same 100mm limit applies to the gap between the bottom rail and the floor.

Building Regulations Approved Document K requires: for dwellings, 900mm minimum for stairs, landings and edges of internal floors. For external balconies and roof edges in dwellings, the minimum is 1100mm. For public/commercial buildings, 1100mm applies throughout. Heights are set by AD K and BS 6180:2011; the horizontal design loads (which rise for crowded areas) come from BS EN 1991-1-1 and its UK National Annex. Always check with Building Control.

Standard post centres are 1.2m to 1.5m for mild steel balustrades. Closer spacing (1.0-1.2m) is used for heavy-duty or public areas. The barrier must resist a horizontal line load applied at handrail height, per BS EN 1991-1-1 (Eurocode 1) and its UK National Annex, as set out in BS 6180:2011: 0.36 kN/m for single-family dwellings; 0.74 kN/m for other residential and non-overcrowded office or institutional areas; 1.5 kN/m for assembly and retail; and 3.0 kN/m for areas susceptible to overcrowding (theatres, bars, malls). Closer post spacing means smaller post sections and lighter base plates.

Posts can be: (1) Base plate bolted to the concrete with expanding or chemical anchors (typically four anchors per plate, e.g. M12) — most common, (2) Side-fixed with a flange plate bolted to the edge of the slab, (3) Core-drilled and grouted into the floor slab — strongest but hardest to adjust. Anchor size, number and the required edge distance are not fixed values: they must be designed to BS EN 1992-4 (design of fastenings for use in concrete) using the load and the chosen anchor's European Technical Assessment (ETA), because edge distance governs concrete breakout. Treat any specific figures as indicative and confirm against the anchor manufacturer's ETA.

For internal use, powder coating (polyester) in any RAL colour is the standard finish. For external use, hot-dip galvanising (to BS EN ISO 1461, typically 85μm) is essential, optionally with a powder coat on top (duplex system). Stainless steel (Grade 316 for external, 304 for internal) is maintenance-free but more expensive.