Step Design

The document to follow for the external steps for a deck is D1/AS1. This document is very detailed laying out the requirement for external stairs. This webpage does not cover every aspect of the building code, but covers the major requirements. There are three main classifications for stairways - public, common and private. For an exterior deck the stairs would be common if this is the main entrance into a house, otherwise it would be private. For the ROBO Deck Designer two different exterior designs are used, please see the detailed images.

To download a copy of D1/AS1 please click here

Step profile

• 37° Maximum pitch
• 190mm Maximum Riser Height
• 280mm Minimum Tread

Some of the other requirements are:

• The top of the step needs to project between 15-20mm
• The risers must be uniform and no more than 5mm variation
• The leading edge of the treads must be a contrasting colour
• The maximum height between risers is 2.5m for common steps or 4m for private steps

Handrail support

There are quite strict regulations on the type of handrails used for steps. Some of these requirements are:

• 900-1000mm high
• The same slope as the stair pitch line
• The profile as shown in D1/AS1 figure 26a

Safety from falling

If a fall of more than 1m is required, safety from falling is a requirement. Please see the building code F4 - Safety from falling. A Ministry of Business, Innovation and Employment Building and Housing Group publication, Guidance on barrier design, provides some design guidance. Please note none of the gaps in the deck are to allow a 100mm diameter sphere to pass through.