An introduction to Understanding the tread, riser, nosing and pitch line.
When working with stairs the only information we have to start with is the total rise or finished floor level (
We explain amongst other information,
why the nosing is not a functional part of the drawing.
The area the nosing occupies.
How to measure the total rise.
The individual rise and going.
How to quickly calculate the minimum going to work with a maximum pitch.
The top tread of a flight is the landing.
Numbering the goings. The common mistakes.
The total rise between floors.
The total rise is a fixed distance calculated by taking the distance between two finished floor levels or ffl as referred to on drawings. This will in effect be the distance between the top of the two floor levels, that the staircase is to span between. Including any floorboards, tiles or other fixed floor finish. This will not include such things as underlay and carpets that may be removed or replaced at any time.
The rise between treads.
The individual rise is the distance from the floor level to the top of the first tread or the top of one tread to the top of the next tread. This will be calculated by diving the total rise by the maximum legal rise to give you the minimum amount of rises required. When the result of the total rise divided by the maximum rise ends in a fraction then the next full number up will have to be used. Once you have this you can calculate your minimum going.
A comfortable rise is at most about 180mm or 7″ when possible it is nice to keep slightly under this.
The traditional riser.
The rise between treads is a vertical dimension between the surfaces of two treads, On traditional or historic stairs the riser is set at 90º to the tread surface and runs from the back of the lower tread and is rebated into the underside of the upper tread. On some modern stairs, the riser is set at an angle less than 90º, this will not change the working dimension between tread surfaces.
The pitched riser.
A modern uptake on the riser is to have it leaning forward at an angle that connects the top of the riser into the front of the nosing. This will not change the position from which the rise is marked. The functional dimension is still taken from the tread surface line at the back of the tread.
The total going.
The going or run is a variable distance, the minimum going shall be calculated to conform with any building codes and regulations that may be set by the authorities in the area to which the stairs are to be fitted.
In the U.K. for domestic properties this is currently 42º, this can be calculated in a few ways.
- Should you have the luxury of modern day CAD software, you can draw this out very easily. Draw a line from point (A) Vertically and equal to the total Rise, up to point (B). Draw a line through point (B) at the maximum pitch angle (Cº) carry this on until it is horizontally level with point (A) and call this point (D). The points A. B. D. create a right angle triangle. The distance (A) to (D) will be distance (E). Distance (E) will be the minimum Going. Any angle greater than (Cº) or minimum Going less than (E) will not be acceptable. Angles and distances greater than these will be acceptable up to a point, dependant on use.
- Use traditional trigonometry. Divide the total rise by The tangent of the pitch angle.
Pitch angle = 42º
Tan of 42º = .9004
Therefore minimum going = rise divided by .9004
Now you have the minimum number of rises (the rise between treads) and the minimum length of going, you can either add treads to reduce the height of each rise, increase the going of each tread to soften the pitch angle or a combination of both. This is all dependant on the space you have to work with.
A comfortable going for private dwellings is around 38º. this will allow you to climb comfortably without walking for miles.
The minimum going = the maximum pitch.
Position of the first going and riser.
The first going will start where the pitch line lands on the ffl that the flight sits on. From this point move into the stair area one going. This will be the face of the first riser and the start of the second going. Once the individual rise has been determined we can draw a line parallel to the lower ffl at a distance equal to one rise to get the first riser position and the start of the second going.
Working in restricted areas.
When working in tight spaces you may be able to soften the angle a bit by setting the first riser at the calculated minimum going position, This helps when a quarter or half space landings are included in the stairs. In diagram 1. you can see the pitch line meeting the ffl (A) at the calculated minimum going, with the riser line (B) set at its correct position for that pitch. we can see here that the pitch angle (C) is greater than the legal pitch angle of 42º.
In diagram 2. We move the riser to the minimum going position (A) and run our pitch line through the top of the rise position (D). This now brings the pitch line back to our legal pitch (E). The bottom going is still there but now moved further into the landing area. With the landing area being greater than the minimum going this is perfectly acceptable.
The number position.
When numbering stairs the going and riser numbers should sit over the appropriate going or in front of the appropriate rise. This will allow for the correct going or rise to be identified from any drawing projection. In this diagram, you can see the correct position for the numbers, for this reason, the first number should be in front of the staircase when looking down on plan. The first tread is the second going. As you read further through this article it will become apparent as to why these numbers sit where they do.
The incorrect number position.
There are so many occasions that the stairs are number with the first tread being numbered as tread 1. yes this may be seen as correct for numbering the treads but this will confuse the drawings. The reason being; when you go to draw the pitch for that tread you will have a conflict of numbers.
When you start to get the pitch for over that tread you will be using tread number 1 with riser number 2. So which number would you then use for the pitch angle?
Marking the first going.
To help explain why the numbering position is important at the manufacturing stage, we have added a diagram showing the pitch board being placed onto the stringer material to mark the goings and risers. From this, you can see that although the first going may be marked onto the stringer, this is more than likely to be cut as finished floor level.
Numbering goings and rises throughout the building.
When numbering the goings and rises for the stairs, it is good practice to number the stairs from going 1 through to the top of the building regardless to how many landing levels there may be. This will avoid any confusion when discussing a certain tread. Also, the stairs are one continuous staircase, the landings are just an unusual size tread. This needs to be taken into account when drawing the stairs and hopefully, help avoid the stairs not meeting the landings correctly.
Number of goings = number of risers – 1
So this isn’t really true, the truth is that the first going is in fact in the landing area at the bottom of the flight, therefore the first going is actually the floor on which the staircase sits or leads into. For this reason generally the first going of each run of stairs is not built with the stairs; as it is part of the structural building, it does still have to be accounted for as a tread during the design stage. During the manufacture of the staircase, the top going is one rise lower than the top landing level. The wall string will usually incorporate the landing nosing from the landing going; this is due to it running over the landing to the skirting or plinth block.
The single going.
The individual going is calculated by dividing the total going by the number of rises. ensure that the minimum going has been calculated by using the total rise and legal pitch angle. The individual going runs from riser line to riser line, anything outside this are is considered decorative and not function for drawing purposes.
The tread and landing nosings.
The tread nosing when drawing stairs or manufacturing is considered a
The top nosing.
The landing nosings.
The landing nosing at the top of a flight is set over the top riser to trim the landing area. This nosing will run around the complete landing facia and terminate in front of the bottom riser for the next flight up or at a wall.
Top nosing and landing nosing with newel post.
When a newel post is used the top nosing is ideally slightly narrower than the newel post this will allow the nosing to be housed into the post at the front face of the post and keep the back of the nosing level with the rear face, thus giving the nosing same overlap onto the landing area as the newel post , this will allow for comfortable positioning of the spindles and make a clean cut at the newel post without having to house the nosing or floorboards around the post. The landing fascia (B) will be in line with the top riser (A). The landing nosings parts (C) and (D) will also align.
Top nosing, geometric.
When the top tread is part of a geometric staircase the riser line will be set in front of the landing trimmer face, this will allow the handrail to flow naturally around the corner from pitch to horizontal or on a continuous flight pitch to pitch.
For the handrail to flow naturally without siting into the landings, the first and last risers (A) will be 1/2 a going (C) outside of the landing fascias (B). This is at both top and bottom of the flight.
Traditional nosing projection.
The traditional nosing has the same projection (X) in front of the riser as the thickness (Y) of the tread. Therefore a tread finishing at 28mm or 1 1/8″ will have a nosing projection of 28mm or 1 1/8″. When working on cut string stairs, the projection beyond the rear riser (Z) is the same as the front riser overhang (X).
The two traditional thicknesses of treads used in heritage staircases throughout the U.K. are 1 1/8″ 28mm or 1 3/8″ 35mm.
The pitch line.
During the drawing and manufacture stages of the staircase the pitch line is drawn through the point between where the tread sits over the riser line to the same point on the next tread, taking the riser line to be a verticle line from the back of the tread.
For handrail fitting.
Due to the different arrangments of tread, riser types and nosing projections in modern strairs, it has become necessary to add another pitch line when measuring the vertical height of the handrail over the treads, this is different to the point used in manufacture. the new pitch line is taken the foremost point of the nosing and the tread surface. This allows for a standard height to be set from that point. With the traditional method of getting the pitch line, the handrail height from the front of the tread would vary, dependant on nosing projection.
Top nosing, bottom going and riser faces working together.
Once you know how the basics work you can start putting them together, one of the basic guidelines for continuous flights is the setting out of the top riser face on one run of stairs and how it aligns with the connecting run. A rule of thumb for any flight that returns straight back on itself is to keep the riser faces from the top riser in line with the first riser from the next run (A). This will help keep the spindles in the correct position over the landing tread. At point (C) you can see where the two handrails would naturally cross over or come to level on the landing. This means the landing fascia would be set into the landing area at line (B) approximately 1/2 a going behind the riser face.
But that’s another chapter. We have covered this briefly in the design stage.