Tempo:
Once the location and width of a stairway and any required landings have been determined, the next step is to figure out the rise and the run. To establish the rise, measure the exact distance between the finished floors of the two storeys under consideration and divide by 184 mm (71⁄4 in.), a comfortable riser height.
A sloped or bevelled edge on leading edges (nosings) makes treads more visible. The size and shape of the slope or bevel is limited by the building code to safeguard against tripping or slipping (see Figure 139).
This calculation gives the number of risers needed over the total rise. Round up the number that results from this calculation to the next whole number. The run is determined by dividing the required number of treads into the total run of the stairs.
Treads and risers are supported on stringers that must be solidly supported, firmly fixed and properly positioned. The stringers may be either cut (see Figures 142 and 143) or ploughed to fit the outline of the treads and risers.
For example, if the total rise is 2 718 mm (107 in.) and if each riser is 184 mm (71⁄4 in.), then 14.8 risers are needed (that is, 2,718/184 = 14.8). Rounding up, 15 risers will be required with each one having a rise of 181 mm (7.13 in.) (that is, 2,718/15 = 181.2). Alternatively 14 risers at 192 mm (7.64 in.) rise would be appropriate when space is limited.
Stringers
Wood stringers must not be less than 25 mm (1 in.) thick when they are supported along their length or 38 mm (11⁄2 in.) when supported only at the top and bottom. The overall depth must be at least 235 mm (91⁄4 in.), and when the stringer is cut out to fit the treads and risers, the portion remaining (the “effective depth”) must not be less than 90 mm (31⁄2 in.) deep.
141 Stairway design
finish floor level
1.95 m (6 ft.- 5 in.) minimum headroom total rise
line of leading edge (nosing)
rise run 90 mm (31⁄2 in.) minimum effective depth stringer finish floor level total run
A sloped or bevelled edge on leading edges (nosings) makes treads more visible. The size and shape of the slope or bevel is limited by the building code to safeguard against tripping or slipping (see Figure 139).
This calculation gives the number of risers needed over the total rise. Round up the number that results from this calculation to the next whole number. The run is determined by dividing the required number of treads into the total run of the stairs.
Treads and risers are supported on stringers that must be solidly supported, firmly fixed and properly positioned. The stringers may be either cut (see Figures 142 and 143) or ploughed to fit the outline of the treads and risers.
For example, if the total rise is 2 718 mm (107 in.) and if each riser is 184 mm (71⁄4 in.), then 14.8 risers are needed (that is, 2,718/184 = 14.8). Rounding up, 15 risers will be required with each one having a rise of 181 mm (7.13 in.) (that is, 2,718/15 = 181.2). Alternatively 14 risers at 192 mm (7.64 in.) rise would be appropriate when space is limited.
Stringers
Wood stringers must not be less than 25 mm (1 in.) thick when they are supported along their length or 38 mm (11⁄2 in.) when supported only at the top and bottom. The overall depth must be at least 235 mm (91⁄4 in.), and when the stringer is cut out to fit the treads and risers, the portion remaining (the “effective depth”) must not be less than 90 mm (31⁄2 in.) deep.
141 Stairway design
finish floor level
1.95 m (6 ft.- 5 in.) minimum headroom total rise
line of leading edge (nosing)
rise run 90 mm (31⁄2 in.) minimum effective depth stringer finish floor level total run
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