What is a lift overrun?
What is a lift overrun?
A lift overrun is the portion of a building’s lift shaft that extends above the top landing of the lift. In other words, it’s the area where the lift car can continue to travel upward if it overshoots the top floor.
How is a lift overrun determined and what is the distance?
The lift overrun is determined by a formula that can be found in the relevant Standard which is BS EN81-20 Safety rules for the construction and installation of lifts. Lifts for the transport of persons and goods Passenger and goods passenger lifts. The actual distance depends on the speed of the lift but for most lifts it is no more than a few hundred mm.
What is the headroom in a lift shaft?
As indicated in the diagram, the headroom is the distance from the finished floor level of the top floor served by the lift, to the underside of the top of the lift shaft. If there are lifting eyes or lifting beams at the top of the lift shaft, then the headroom dimension is taken to the underside of these.
How much headroom is needed?
This depends on a few factors but the most significant one is the speed of the lift. For a typical lift speed of 1 m/s the lift headroom might be getting on for 4 m. Which is typical in buildings of half a dozen or so floors. As the building height increases, usually, so does the lift speed and the lift headroom. In the majority of instances for buildings up to 25 floors or so, the headroom will be in the order of 5m to 6 m.
Why is the headroom dimension much larger than the actual lift overrun?
For safety reasons. When the lift is in an extreme position at the top of the lift shaft i.e., it has overrun and over travelled past the top floor. In this case there must be what is termed a refuge space for an engineer who may be working on the lift when it overruns. The refuge space is necessary so there is no risk of them getting crushed between top of the lift car and the top of the lift shaft if in the extremely unlikely scenario, the lift overran whilst they were working on the car top.
How much refuges space is needed on lifts?
There are two possibilities for the refuges space, upright and crouching. This is best illustrated with reference to the diagram. For the upright posture the horizontal distance is 0.4 m x 0.5m and for the crouching posture it is 0.5 m x 0.7 m. The height is indicated on the diagrams. The numbers 1, 2 & 3 refer to the colours black, yellow and black for a sign to indicate the presence of the refuges space.
Why is the lift headroom critical in building design?
The lift headroom is a critical dimension in building design. If there are floors above the lifts then this can infringe spatially on those. If there are not then, the headroom can affect the roofline of the building which may well be a planning concern.
How can we help you with your lift design?
Whether your project involves a single lift or multiple lifts we can advise on spatial planning. We are well accustomed to following RIBA plan of work and do so on projects day in day out. We can assist throughout the whole process or, at individual stages. Typically, if we are not working throughout the project, we might provide the necessary design input at stage 3 leading to a vertical transport stage 3 report. Often, this stage will support the planning application.
We would love to talk to you about your project. And, we are more than happy to engage in a no obligation discussion to understand your needs, and how our input can best add value to your project.
