Many people ask this when aiming to minimise costs, but there are many factors to consider when deciding the depth of stair nosings.
Australian Standards require all stair nosings to have a depth of at least 50mm. When on a mission to reduce costs it can be tempting merely to comply with requirements, but there are reasons why narrow nosings can compromise functionality, safety and longevity - drawbacks that will ultimately cost more money.
The best approach is to select a depth that achieves the optimum balance between economy and performance.
Why is depth important when it comes to stair nosings?
When ascending stairs, the foot makes deeper and flatter contact on the tread, so the deeper the nosing the better. Safety Step recommends a minimum depth of 75mm. Explained below are some of the reasons why 50mm stair nosing depths are problematic:
1) Trip Hazards
Industrial stairs almost always have a pronounced radius at the leading edge. This often results in the nosing sitting flat on the tread, lifting at the rear and creating a trip hazard at the back of the nosing. A deeper stair nosing, of at least 75mm, will sit much more neatly, tightly and safely.
2) Difficulty with fitting narrow nosings
Narrow (50mm) stair nosings are difficult to fit to open grate steel treads. It's even more difficult when the tread has a welded-in, radiused front edge. The cost associated with increased installation time, far outweighs any drop in material costs.
3) Increased downward shearing action
Narrow nosings increase the downward / forward shearing action on stairs. The narrower the nosing, the greater the increase. This higher shearing action causes 50mm deep nosings to pull loose from timber treads and 'plug & screw' methods in concrete. Deeper nosings of at least 75mm are significantly more reliable as the fixings are located further back.
4) Narrow nosings aren't suitable for "high accident risk" areas
It's important to consider the level of "accident risk" associated with industrial stairs. The higher the risk = the deeper the stair nosing. If stairs suffer localised soiling from foot traffic, then a deeper nosing is recommended. The same advice applies to exterior stairs that are exposed to the elements. Exterior stairs should have higher spec nosings than interior nosings. As a minimum, use 75mm nosings and in very high risk areas, use 150mm deep nosings.