Approved Document K and Stair Nosings: Geometry, Not Contrast

Approved Document K is the most frequently misquoted document in stair nosing specification. It is cited constantly as the source of contrast and visibility requirements. It is not.

Part K covers geometry. Contrast comes from Approved Document M, with BS 8300-2:2018 supplying the number.

What Part K actually covers

Approved Document K is titled Protection from Falling, Collision and Impact. In relation to stairs it deals with the physical dimensions and arrangement of the flight:

  • Going — the depth of the tread from front to back
  • Rise — the height of each step
  • Consistency — rise and going should be uniform through a flight, because an inconsistent step is where people fall
  • Nosing projection — how far the leading edge may overhang the tread below
  • Handrails, guarding and headroom

The number that matters for nosings

For stair nosing specification, the Part K figure to work to is a maximum projection of 25mm over the tread below.

The reason is straightforward: an overhanging nose catches the toe of a shoe on ascent. The bigger the overhang, the more likely the catch, and the more likely a fall. This is also why Part K addresses open-riser stairs specifically — treads on an open-riser flight are expected to overlap so a foot cannot pass through the gap.

In practice this constrains profile choice on shallow treads. A deep nosing on a stair with a tight going eats into the walking surface and can push the projection past what is acceptable. Measure the going before choosing a width.

Where the confusion comes from

Three things drive the misattribution.

Part K and Part M are often read together, because a stair being designed properly is being checked against both at once. Suppliers then quote them as a single requirement.

Part K does concern itself with stairs being safe to use, and edge visibility is obviously part of safety, so the leap feels natural even though the document does not make it.

And the error is self-reinforcing. Once enough supplier pages say "Part K contrast requirements", specifiers repeat it, and it appears in tender documents. We have found it in our own older copy, which is why this page exists.

Why the distinction is worth getting right

If you specify against Part K believing it covers contrast, you have no dimensional target — because Part K does not give one for contrast. The 55mm band and the 30-LRV difference come from Part M and BS 8300 respectively, and if you have not looked at those you have not specified contrast at all.

Conversely, a specification that nails contrast beautifully but ignores Part K can still fail: a 70mm nosing on a shallow domestic going may project too far and reduce the usable tread.

How Part K, Part M and BS 8300 fit together

  • Part K — the shape of the stair. Going, rise, 25mm maximum projection.
  • Part M — who can use it. The 55mm × 55mm contrasting band, for buildings other than dwellings.
  • BS 8300-2:2018 — how much contrast counts. At least 30 LRV points, as a recommendation rather than law.
  • Regulation 12 of the Workplace Regulations 1992 — the surface must not be slippery. This one is law and applies continuously.

Frequently asked questions

Does Part K require contrasting stair nosings?
No. Part K covers stair geometry. Contrast comes from Approved Document M, with the 30-LRV figure from BS 8300-2:2018.

What is the maximum nosing projection under Part K?
25mm over the tread below is the figure to work to. A greater overhang increases the risk of catching a toe on ascent.

Does Part K apply to existing stairs?
The Building Regulations are triggered by building work, so an untouched existing stair is outside them. Regulation 12 of the Workplace Regulations and the Equality Act duty still apply to how it performs in use.

Does Part K apply to domestic stairs?
Yes, for new build and material alterations — the geometry provisions cover dwellings. It is Part M's contrast band that is limited to buildings other than dwellings.

See the full compliance guide for how these fit together, or browse stair nosings by profile and width.