The two figures are six millimetres apart and the flight passes one and fails the other. Six millimetres is below the resolution of a tape read at arm's length, which is why the reading has to be taken with a square edge and recorded with the edition.
Nosing projection: 32 mm against 38 mm on the same flight
written 2026-09-08kept by The Nosing Line (a named line, not a person)
What was measured
A straight flight of thirteen risers in a plant room, built in the mid-1990s, with a cast nosing profile on each tread and a painted steel stringer. Three treads were measured at the walk line with a steel rule and a straight edge on the pitch line, and the readings were 31 mm, 31 mm and 32 mm.
| Reading | Tread 2 | Mid flight | Tread nā2 |
|---|---|---|---|
| projection | 31 mm | 31 mm | 32 mm |
| over the tread below | yes | yes | yes |
| wear lip | none | slight | none |
Why the comparison is not straightforward
The British approved document puts the tread overlap at no more than 25 mm, so this flight is six to seven millimetres over the maximum under that document. The American accessibility standards do not print an overhang figure and instead govern the leading edge and the tread surface, so the same flight raises a different question there. The workplace rule does not print an overhang figure either. The 32 against 38 comparison is between a range that permits up to 38 mm and one that caps at 25 mm, which is a wider gap than the headline numbers suggest.
What was decided
The flight was recorded as a dated deviation rather than a defect. The stair was built under an earlier edition, it is in a plant room with infrequent traffic, and no wear lip was found on two of the three treads. The record names the edition, the three readings and the decision, and it is filed against the flight rather than against the clause.
The mid-flight tread carried a slight wear lip. That is the reading that will change: the lip will be dressed at the next refurbishment and the projection will drop by a millimetre or two. A record that does not describe the lip will look wrong when it is re-read after that work.
What this record does not say
It does not say the stair is unsafe. It does not say the projection should be altered. It says what three treads measured, which document each figure belongs to, and who decided what happens next.
Documents checked
- 1Safety on Stairs (NBS Building Science Series 108)supports the historical stair-safety work the earlier edition of this flight was written under
- 2CROSS Safety Report: Failure of cantilevered stone staircase (The Structural Engineer, IStructE)supports the structural-failure reporting practice that a dated record follows
- 3Stair Gait in Older Adults Worsens With Smaller Step Treads and When Transitioning Between Level and Stair Walking (Frontiers in Sports and Active Living)supports the evidence that tread size changes how a stair is walked
Each line points at one specific document, with its own title as the link text. No line is a home page and no line is a search result.
File this and go Close this bulletin once you have the three readings and the edition. The rest is a decision, and the decision is recorded separately.