Manual of Purpose-Made Woodworking Joinery

108 Designing and making stairs to current building regulations

length. They are recommended by BSI (the British

Standards Institute) to have a sectional size of not

less than 38mm × 38mm and a minimum length of

75mm. For stairs up to 900mm wide, at least two

blocks per step should be glued and rub- jointed to

the internal angle between each tread and riser – at

the separate stage of step- construction (described

later).

Timber quality

If the quality of the timber is to meet the British

Standard, BS 585 refers to BS 1186: Part 1: class 3,

which list requirements of grading. This will mean

careful selection of the staircase timber, as class 3 does

not refer to commercial grading descriptions.

Making step templates

Figures 6.34(a)(b)(c)(d)(e): Although a traditional- type

steel roofing square with adjustable stair- gauge fittings

• Figure 6.34(a) – was effectively used to set out the
  steps on stair strings (especially by site- carpenters
  setting out formwork strings for in- situ concrete
  stairs), not all joiners had these tools and – prior to
  modern plastic- laminate stair- template jigs, now widely
  used with heavy- duty portable powered routers –
  wooden- , then plywood- , then hardboard- templates
  were made for setting out the exact step positions on
  the stair- string boards. As the updated template is still
  used, the knowledge- related progression of these is
  shown below, from 6.34(b) to (d).

Glue blocks

As shown in Figures 6.33(a) to (d), triangular blocks

(referred to as ‘glue blocks’) are an important part of

the structure of all wooden or composite- boarded

steps and they are produced by ripping through a

length of 50 × 50mm par timber diagonally (with

the aid of a saw- bench jig), prior to crosscutting to

Figure 6.33 (a) In theory, because the tread is only

butt- jointed to the plywood riser, if it shrinks across the

grain, there is a likelihood of a gap appearing against

the riser face. Note that illustration (a) shows the hypot-

enuse of the step- triangle at (H), the length of which is

used to multiply the number of steps to determine the initial

length of the strings. There would of course be additional

allowances for either newel- post tenons, or – in the case

of wall strings – projections to intersect with the upper and

lower skirting boards. Also note that the hypotenuse at (H)

becomes an important ‘margin line’ when setting out the

steps (to be covered in following paragraphs); and (b)

this method of jointing allows each board to shrink slightly

(in the direction of the arrows) without splitting or showing

unsightly gaps. Such gaps might not concern the majority

of people who carpet their stairs, but there are others who

prefer wooden stairs – in softwood or hardwood – to be

fully exposed.

Figure 6.33 (c) This method of jointing is similar to (b),

regarding shrinkage- design, but the nosing appearance is

made more ornate by the insertion of a so- called ‘scotia

mould’ (traditional terminology for a ‘cavetto mould’); and

(d) this method of jointing allows the riser to shrink, but not

the tread board.

(H)

(a) (b)

(c) (d)

Figure 6.34 (a) A steel roofing square (now called a metric

rafter square, sized 610 × 450mm) in position – with a

set of separate stair- gauge fittings (still available) attached

to the ‘tongue’ and the ‘blade’ seated on the face of a stair

string being marked out. Note the dotted line represent-

ing the margin needed to accommodate the tread- nosing

projections; and (b) a triangular pitch- board with a separate

margin- template. As seen in Figures (c) and (d), the margin

template eventually became a part of the pitch- board.

Margin

template

Pitch

board

(a) (b)