Manual of Purpose-Made Woodworking Joinery

96 Designing and making stairs to current building regulations

Alternative approach

AD K1 states that the requirement for steepness of

stairs can also be met by following the relevant recom-

mendations in BS 5395 Stairs, ladders and walkways:

Part 1: 1977 Code of practice for the design of straight stairs.

Level steps and open risers

Figure 6.12: Steps should have level treads and may

have open risers, but treads should then overlap each

other by at least 16mm. For steps in buildings provid-

ing the means of access for disabled people, reference

should be made to Approved Document M (AD M):

Access and facilities for disabled people.

All stairs that have open risers and are likely to be

used by children under 5 years of age should be con-

structed so that a notional sphere of 100mm diameter

could not pass through the open risers.

Headroom

Figures 6.13 and 6.14: Clear headroom of NLT 2m

measured vertically from the pitch line to the soffit

of the stair above, or to the corner- edge of the bulk-

head of the landing, etc, must be achieved. For loft

Pitch line

Figures 6.7 and 6.11: This is a notional (imaginary) line
used for reference to the various rules, which connects
the nosings of all the treads in a flight and also serves
as a line of reference (in a midway, central position)
for measuring the regulatory stair- formula known as
‘2R+G’ (see Figure 6.22) on tapered tread steps.

Helical stair

A stair that describes a helix around a central void
(with an open stairwell). Such a stair is traditionally
known as a geometrical stair.

Spiral Stair

A stair that describes a helix around a central support-
ing column (without an open stairwell).

General requirements for stairs

Steepness of stairs

In a flight, the steps should all have the same rise and
the same going to the dimensions given here further
on for each category of stair in relation to the 2R+G
formula.

Central

pitch

line

NLT 220 mm

going

2R+G

NMT 42º

pitch

50mm

minimum

tread

width

Figure 6.11 Pitch line related radially on tapered steps;
and the minimum ‘tread- width’ of 50mm – somewhat
relaxed from a previous K1 reference to the minimum
‘going’ being NLT 50mm. Note the abbreviations NLT =
not less than, and NMT = not more than.

NLT 16 mm

Non-entry area for notional sphere of 100 mm diameter

Figure 6.12 Open- riser stair restrictions.

Headroom

NLT 2 m

Headroom

NLT 2 m

Figure 6.13 Minimum Headroom required from notional

pitch line of NLT (not less than) 2m.