What is the 100mm sphere test for balustrades?

BS 6180 requires 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. Typically, bars at 95-98mm clear spacing are specified. This applies to the gap between the bottom rail and floor too.

What height should a metal balustrade be?

Building Regulations Approved Document K requires: 900mm minimum for stairs, landings below 600mm fall height. 1100mm minimum for landings, balconies, edges of floors, and any location with a drop over 600mm. For public buildings or areas where crowd loading is possible, BS 6399-1 may require even higher barriers. Always check with Building Control.

What post spacing should I use?

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 post must resist a horizontal line load of 0.36 kN/m (domestic) or 0.74-3.0 kN/m (public/commercial) per BS 6399-1. Closer spacing means smaller post sections and lighter base plates.

How should balustrade posts be fixed at the base?

Posts can be: (1) Base plate bolted with 4× M12 expanding anchors into concrete — 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. For side fixing, ensure sufficient edge distance (minimum 75mm) to prevent concrete breakout.

What finish should I specify for metal balustrades?

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.

TradeCalculator

Metal Balustrade Calculator — Posts, Handrail & Infill Bars

Calculate metal balustrade requirements including post centres, infill bar spacing to pass the 100mm sphere test per BS 6180, handrail section, and base plate fixing.

Total Balustrade Length

Total run of balustrade

Balustrade Height

1100mm for balconies, 900mm for stairs

Post Spacing

1.2-1.5m typical centres

Price Per Metre Run (optional)

Your quoted price per metre installed

How We Calculate This

This calculator determines the components needed for a metal balustrade installation, ensuring compliance with BS 6180 and Building Regulations Part K.

Key requirements

Height: 1100mm for balconies and floor edges, 900mm for stairs
100mm sphere test: No gap wider than 100mm clear (BS 6180)
Post centres: 1.2-1.5m standard, based on loading requirements
Handrail: 48.3mm CHS standard, grippable profile required

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.