Centreline is king.
An introduction to The handrail centre line rule.
This is the most important yet much missed rule for drawing geometric stairs, without following this rule the handrail and stairs may not work correctly. This is even missed on straight flights with cut strings and newel posts.
The edge of the staircase and the positioning of the risers around the turns is all controlled by the centre line of the handrail down through the balusters, glass or spindles. Some handrails may sit over the treads others will sit into the stairwell. The handrail will not move but the stringers will.
Many people have commented that only a handrailer would consider the handrail the most important part of the stairs, however for the handrail to flow properly you have to consider the handrail as the house and the stairs as the foundations that the house sits upon. It is no use putting down the foundations for a shed and expecting to have a mansion built on those foundations.
In order to have the handrail flow properly, you will need to confirm the handrail flow, this will mean drawing a 2D stretch out of the flight through the centre line of the handrail, the 2D stretch out will show you the flow of the handrail and stairs.
Once you have your stretch out you can transfer that to the plan view of the stairs you wish to draw, when you have the plan view drawn to the centre line of the handrail you can calculate the edge of the stairs and the positioning of the risers. The edge of the stairs may move in or out of the stairwell dependant on the medium used to support the handrail.
Setting the handrail centreline.
In geometric stairs, the handrail centreline will control the flow of the handrail, by changing the distance between parallel flights you can change whether the handrail stays at the same pitch as the pitch in the straight flights or if it comes to level mid-turn.
Transfering the handrail centreline to the staircase.
Distance between Stringer faces – handrail set on spindles.
In Diagram 1 you can see the handrail set on spindles, the centre line of the two handrail runs is X, the spindle centre line will sit directly in line with the handrail centre line.
In a typical spindle set up, the stair well side of the spindle will sit in line with the stair well stringer face, therefore the stringer face will be half a spindles width “Z” towards the stair well on each run or 2 x half a spindles width.
This means the stringer faces will be the distance between the handrail centre lines “X” less twice half a spindles width “Z”.
Distance between Stringer faces = X – 2 x Z
Distance between Stringer faces – handrail set on stringer mounted glass or Balusters.
In Diagram 2 you can see the handrail set on a stringer mounted support, the centre line of the two handrail runs “X” as in Dia 1. The support centre line will sit directly in line with the handrail centre line.
In a typical stringer mounted support for the handrail the support will clear the nosing with about 12mm or 1/2″ of clearance, you will also have 1/2 of the supports width to add to the stringer face offset “Z”. In this situation, the stringer faces will move away from the stair well.
This means the stringer faces will be the distance between handrail centre lines “X” plus twice the offset from support centre line to stringer face “Z”.
Distance between Stringer faces = X + 2 x Z
Distance between Stringer faces – handrail set on curved support.
In Diagram 3 you can see the handrail set on a stringer mounted support, the centre line of the two handrail runs “X” as in Dia 1. The support centre line varies from the handrail mount postion to the stringer mount position.
In this situation, you will need to calculate the support offset to determine the “Z” or stringer face position. This is calculated by taking the distance between the handrail centre line and the support centre line at stringer height “A” minus the distance from the support centre line to the face of the stringer mounting plate, distance “B”.
A – B = Z
Dependant on the support offset the stringer face may move in or out of the stair well.
When “A” is greater than “B” then the Distance between Stringer faces = X – 2 x Z
When “B” is greater than “A” then the Distance between Stringer faces = X + 2 x Z
The staircase is generally the largest item in the house, it is best when possible to design the stairs before committing yourself to the doors etc. on the landings: this will allow you to design the stairs and landings with the correct setting out.
A staircase with half space landing is not two straight flights of stairs with a landing between. It is one continuous flight. The landing is just a larger tread than the others.
Number the rises consecutively, from the lowest in the property to the top rise in the property. This will avoid misunderstanding throughout the project.
numbering rises in each individual flight may lead to error.
Centre line setting out:- Newel post.
The stretch out explained. (coming soon)