Stair nosings: the projection rule, wear, and the scotia
Parts Glossary & Jargon Buster
Written by Scott Jones, The Stair Guys, independent staircase measuring and sourcing specialists·Last updated
The nosing is the front lip of each tread, the bit that projects out slightly over the riser below. It looks like a small detail, but it does three jobs, and it is the part of the staircase that gets the hardest use of all.
What it is for, and how far it can project
The overhang is not just for looks. It adds a little to the effective depth of the step, giving your foot more to land on, and it gives a clear edge to the step so you can see where each one ends. The projection is limited by the regulations, up to about 25mm in England, so a nosing that sticks out too far, which people can catch a toe on, is not allowed. On an open-riser stair the same edge has an extra job, keeping the treads overlapping, covered in open-riser staircases, and the full set-out is on the stair dimensions page.
Wear and grip: the part that has to be done
Because it is the leading edge, the nosing takes the most traffic and wears first, which is why a film finish wears through at the nosing before anywhere else, as covered in finishes. It is also where grip matters most. Whatever you do about slip, an anti-slip strip, a textured nosing, a contrasting edge to make each step visible, has to actually be applied at the nosing to do any good; it is a functional thing, not a finishing touch to skip. That matters most where anyone less steady or less sighted uses the stair.
The scotia
Underneath the nosing, in the internal angle where the front of the tread meets the top of the riser, you will often see a small curved moulding. That is a scotia (also called a cove or cover mould). Its job is to finish that joint neatly and hide any small gap, so it is a tidy, functional detail rather than a structural one.
Frequently asked
What is a stair nosing?+
The nosing is the front edge of a tread that projects out over the riser below. It adds a little to the depth your foot lands on, gives a clear edge to each step, and on an open-riser stair keeps the treads overlapping. It is also the part of the staircase that wears first, because it takes the most traffic.
How far can a stair nosing project?+
Up to about 25mm in England under Approved Document K. The overhang gives extra foot room and marks the step edge, but too large a projection is a trip hazard, so it is capped. The nosing detail is part of the overall stair set-out.
What is a scotia on a staircase?+
A scotia, also called a cove or cover mould, is the small curved moulding fitted underneath the nosing, in the angle where the front of the tread meets the top of the riser. It finishes that joint neatly and hides any small gap. It is a tidy, functional detail rather than a structural one.
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