Perhaps, you have sometimes noticed that it is convenient for you to go up some staircases, and you do not apply much force to go up, and going up other staircases becomes difficult and dangerous. It is directly connected with correlation between riser height (hereinafter r) and going (hereinafter g).
This correlation determines the pitch angle of stairs, and if it is essential to provide for convenience and safety, one shall adhere to the rules of staircases design.
- 0-9° entrance ramps
- 9-26° flat stairs
- 26-33° convenient and comfortable staircases for a dwelling house
- 33-41° less convenient staircases for a dwelling house
- 41-75° step ladders and compact stairs
- 75-90° emergency stairs and accommodation ladders
As far back as in 1771 the French architect Jacques-François Blondel in his book Cours d'architecture for the first time described the correlation between riser height and going. He described it as 2 x rise + going = step length. This correlation was based on his observations over the step length in horizontal plane and leg raise in vertical plane. The step length is considered to be an average step length of an adult person by regular walking along the horizontal plane, and it has a value from 60 to 64 cm. Convenient leg raise in vertical plane makes about 31 cm. Based of these figures, the rule of a step size is deduced. They still use this rule nowadays. The stairs with a pitch between 30 and 70 degrees are designed according to this rule. If you apply it to very flat stairs or vice versa to very steep ones, they will have either too narrow or too deep treads. At that you shall remember that staircases with a going less than 26 cm and more than 32 cm are inconvenient and dangerous for walking. Therefore this rule cannot be considered universal. Besides the rule of a step size there exist two more rules: the rule of convenience and the rule of safety. The rule of convenience is defined as g - r = 12, and it is applied for design of stairs with a pitch angle of about 30 degrees. The values of 16/28 , 17/29 can serve as an example. The rule of safety is defined as g + r = 46, and it can be applied for staircases with different pitch angles. When we design the staircase according to this rule we receive the pitch value that is between the value received under the basic rule (based on the step length) and the value received under the rule of convenience. The values of 15/3 1, 16/30, 17/29, 18/28 can serve as an example. Experience shows that staircases with a riser height less than 15 cm and more than 18 cm are inconvenient for going up. There exist other correlations between rise height and going, but they refer to utility rooms and will not be described here.
As you have already noticed the correlation of 17/29 complies with all three rules and is the most comfortable for going up.
The correlation between riser height and going shall be the same throughout the length of the flight of stairs. Indifferent countries some building regulations allow to broaden these norms a little, but we will adhere to the values received precisely according to the rule of safety. The drawings of staircases proposed in the section Stair Plans are also made on the basis of these values.
As you can see from the figure below, the shorter the going is, the less space is occupied by the staircase on the plan, but along with this the riser height increases. Or vice versa, the longer the going is, the more space is occupied by the staircase on the plan, but along with this the riser height decreases.
Fig. Going Influence on the stairs dimensions
Now let's discuss in detail basic rules, terms and dimensions one shall know prior to staircase building.
Stairs Flight Parameters
Middle line of the flight is an imaginary line passing in the center of the flight of stairs, on which the goings are marked in the process of design. The beginning of the line is marked with a small circle, and the end of the line is marked with an arrow, showing the flight direction.
Fig. Middle line of the flight
Walk line is a zone of the flight with guaranteed minimal and maximal width of the going required for comfortable walking. The wider it is, the more comfortable it would be to walk. For straight flights it can be the entire useful width. For curved flights the inner edge of the walk line shall not be closer than 305 mm to inner edge of the flight. At that the minimal size of the going at this distance shall be not less than 255 mm. Spiral stairs have the smallest walk line. Its area lies between the pitch line and the line drawn at the distance of 1/3 from the outer side of stairs.
Fig. Walk line
Horizontal plane serving as a support for walking is called a tread.
We have studied the width of the going above, and the methods of design of staircases with wedge-shaped treads will be described in the section How to calculate stairs. Here we want to describe general parameters of treads which are common to all staircases. It should be noted that there exist the full depth of the tread and the going. The difference between these two parameters is the following: the depth of the tread is the full depth of the tread itself as a constructive element of a staircase, and the going is a visible depth of a tread on the plan, i.e. the distance between the butts of treads. The depth of the tread is always more than the going.
Previously glued wood serves as a material for manufacture of tread. The front surface of the tread may be veneered with thin strips of whole timber. It is not recommended to use whole timber planks, because they will be prone to deformations. Minimal tread thickness shall make 42 mm for closed string stairs with risers, and 50 mm for closed string stairs without risers and for open string stairs.
Fig. Stairs tread
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