Assessing and documenting handrail lines are one of the critical steps for architects and designers to correctly specify a set of stairs. However, issues arising from an incorrect or unachievable handrail line represent some of the most common problems that arise when stairs go to contract.
Let's review the key requirements of stairway handrails as specified by the AS-1428 Access and mobility code:
- Handrails must be installed on both sides of the stairs
- According to the code, handrails may not transition to vertical on any sections of the stair
- Handrail must run parallel to the stair nosing line
- When a handrail terminates at the bottom of flight, the handrail must extend at least 300mm from the point at which the nosing line intersects with the bottom floor level (see diagram).
- The handrail must extend a minimum of 300mm horizontally past the nosing of the top riser, but when the handrail is continuous, this does not apply to the inner handrail on intermediate landings.
- Handrail heights are measured from the nosing line or finish floor height to the top of the handrail.
Stair handrails often connect with handrails or balustrade around the void edge, and usually considered part of the same package. It is often the case in commercial buildings that the handrail height on level floors is not necessarily the same as the handrail height on the stairs, as measured on the raking nosing line. This may be for geometric reasons, but also from a human use perspective, the perceived height of a handrail on a rake is actually higher than drawn. This is because one is moving forward (up or down) the flight. Accordingly, the handrail is often specified lower on the raking sections than on the level sections.
This being the case, architects and designers should be aware that, by simple geometry, the crank or inflection point of the handrail is generally not directly above the inflection point of the walking line. Depending on the detail of the balustrade, neglecting this point could lead to problems down the track.
This issue is in fact just one example of the many cases in which detail lines on the stair cannot be assumed to change direction from raking to level at the same horizontal location. For instance, consider a stringer line for which the design logic dictates is running at common offset from the nosing line. The offset (measured perpendicular) yields different vertical offsets for the treads and the landings by simple Euclidean geometry, and means that the stringer will transition to horizontal at a further point than the nosing line. If space has not been allowed, then there may be problems detailing as these architectural lines arriving at the correct level. For example, a stringer, handrail, soffit, or other component may be expected to turn 90 degrees at a horizontal point before it has reached the correct level.
The take home messages
- Do not assume raking lines inflect at the same horizontal point.
- As you begin detailing, always allow for an 'outstep', that is a nominal offset at the top and the bottom of the nosing line. Be aware of what lines are determined by offsets with respect to the nosing line, and which ones have differential vertical measurements on the rake and the level.
- When allowing space for a staircase (ie in specifying a stairwell) always leave some extra space for raking lines to meet with horizontal lines.
Published on: 25-Mar-2011. Topic/s: