What are the dimensional requirements for external stairs per BS 5395?

BS 5395-1 and Building Regulations Part K require: riser 150-220mm (private), 150-190mm (utility/commercial). Going 220-300mm (private), 250-400mm (utility). The 2R + G formula should give 550-700mm. Maximum pitch is 42° for private stairs and 38° for utility stairs. Minimum clear width is 900mm for external escape stairs.

Why do external stairs need handrails on both sides?

Building Regulations Part K requires handrails on both sides for stairs wider than 1m in non-domestic buildings and for all external escape stairs. The handrail must be between 900-1000mm above the pitch line and between 900-1100mm above any landing. Both handrails must be continuous and grippable (typically 48.3mm CHS tube).

Should an external steel staircase be galvanised?

Yes, hot-dip galvanising to BS EN ISO 1461 is essential for external steel stairs in the UK. A typical 85μm zinc coating provides 25-40 years protection depending on the environment. For coastal or industrial locations, a duplex system (galvanising + powder coat) is recommended. Never rely on paint alone for external steelwork.

What tread material is best for external stairs?

Open mesh grating (Weldlok/Webforge) is the most common for industrial and commercial external stairs — it is self-draining, non-slip, and allows light through. Durbar checker plate with drainage holes is another option. Both must have a non-slip surface per BS 8300. Avoid smooth surfaces that become slippery when wet.

Do external fire escape stairs need fire rating?

External fire escape stairs within 1.8m of an unprotected opening in the building facade need 30-minute fire protection. However, if the stair is far enough from the building face (over 1.8m), or the adjacent wall has fire-resistant construction, no fire protection is needed. Galvanised steel without fire protection is the typical solution for detached external stairs.

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External Steel Staircase Calculator — BS 5395 Compliant Design

Calculate external steel staircase requirements per BS 5395: rise/going compliance, flight width, handrails both sides, galvanising area, and estimated weight.

Floor-to-Floor Height

Total height from ground to landing

Stair Width

900mm minimum for escape stairs

Riser Height

150-190mm for utility/commercial

Going Depth

250-400mm for utility/commercial

How We Calculate This

This calculator designs an external steel staircase per BS 5395-1, checking dimensional compliance and estimating material quantities including galvanising area.

Compliance checks

2R + G rule: Twice riser plus going = 550-700mm
Maximum pitch: 42° (private), 38° (utility/commercial)
Minimum width: 900mm clear between handrails
Handrails: Both sides, 900-1000mm above pitch line

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.