Exterior stair design essentials
Outdoor stairs must deal with weather, moisture, frost and heavy use. This guide focuses on safe geometry, materials and drainage that actually work over time.
Recommended exterior rise and run
- Rise: 120–170 mm
- Run: 280–350 mm
- Angle: 25°–33°
Shallower proportions improve safety in wet and icy conditions.
Drainage and water control
- Provide a 1–2% fall on each tread toward the open side.
- Use open risers only if allowed by local codes.
- Install drains at landings where water can accumulate.
Materials
Concrete
Durable and stable. Add anti-slip nosing or texture.
Natural stone
Visually strong but can become slippery. Choose flamed or bush-hammered finishes.
Timber
Requires periodic treatment. Use hardwood or durable species.
Metal (steel/aluminium)
Good for modern exterior flights. Use perforated treads to prevent water pooling.
Slip resistance
- Slip-resistant nosings
- Textured or flamed surfaces
- Drainage grooves
- Non-slip coatings (reapplied periodically)
Winter conditions
- Install snow-melting mats or heated treads in high-traffic areas.
- Avoid materials that absorb water and freeze.
- Ensure handrails on both sides for icy climates.