1. GCSE Construction & The Built Environment
Domestic Stair Design

2. Function
The function of stairs is to provide easy walking access from one floor or level to another in safety.
Stairs must be strong enough to carry the weight of people using them and also the weight of any equipment or furniture being moved from one level to another.
Stairs must be fire resistant for a sufficient length of time to provide a safe means of escape for the occupants of the building. –

3. Stair Terminology
Some of the main terms associated with stair construction and design are:
Stairs: The number of steps and landings leading from one floor level to another.
Stairwell: The space occupied by the stairs.
Flight: Continuous set of steps from one floor to another floor or to a landing.
Landing: Platform between two flights to serve as a rest. Also used to change the direction of stairs.

4. Component Parts Tread:
The upper surface of a step (where the foot is placed).
Riser:
The vertical member connecting two treads.
Nosing:
The distance that treads project beyond the riser usually.
Step:
It consists of the tread and riser supported by the strings. The number of steps is governed by the floor height.
Going:
The horizontal distance between the face of one riser and the face of the next.
Rise:
The vertical distance between the top of a thread and the top of the thread above or below it. The rise of a flight is the overall height from the finished level of one floor or landing to the finished level of the adjoining floor or landing.

5. Component Parts
Nosing 16mm min.
Pitch line
Going 220mm min.
Rise 220mm max.
Pitch 420 max

6. Headroom
Minimum headroom 2000 mm

7. Landings
Landing at bottom of stairs at least 400mm clear of door swing.

9. Stair Design
Of the many aspects to be considered when a stair is designed,
the following should receive prime consideration:
The fitting of the proposed stair – whether there is enough room.
Construction and installation details must conform with current building regulations.
Suitable material for the stair members.
The finished appearance (aesthetics).

10. Stair Design
There should not be more than sixteen risers in any one flight. This is the maximum number of steps that the average person can climb safely without requiring a rest. A flight containing one or two risers should be situated at the bottom of the stairs.
The rise for the step is calculated by dividing the overall rise by the chosen number of risers.
The going for the step is selected to suit the available floor area while ensuring that, together with the rise, the Building Regulations are complied with.
The number of steps in any one flight will be one less than the number of risers. This is because the last riser connects with the landing.

11. Where R: Riser & G: Going
Stair Design Example
Going (G): 220 mm min. (250 mm optimum).
Rise (R): 220 mm max. (175 mm optimum).
Pitch: max (350 optimum).
To comply with the Building Regulations the following formula is used:
(2R+G)
Where R: Riser & G: Going
Should be between 550mm and 700mm.

12. (These dimensions are taken from working drawings)
Example
Height between floors: 2650mm
Distance Available: 3350mm
(These dimensions are taken from working drawings)
Solution Check
Take 14 risers: (2R + G) = 550 – 700mm
2650 / 14 = 189mm = 636mm
Gives 13 treads:
3350 / 13 = 258mm
Now check the Pitch – 42 degrees max.

13. Pitch: Mathematical Terminology
The sine (sin), cosine (cos) and tangent (tan) of angle theta are defined by the lengths of the sides of the triangle: (trigonometric ratios)
S.O.H.
Hypotenuse
C.A.H.
Opposite
T.O.A.
Theta
Adjacent

14. Pitch We use trigonometrical ratios to find C:
tan C = A B = = 0.73
B C
C = tan (0.73) = 36 degrees mm
(max pitch 42 degrees)
258mm

15. Student Activity
Using trigonometrical ratios calculate the pitch of stairs, where the going is 240mm and the rise 195mm
Explain how this stair complies with current Building Regulations NI 2012