One lift above 12 metres is a single point of failure

Ask a lift company how many lifts a residential building needs and you will get a traffic answer. Ask what happens when one of them is out for three weeks and you will usually get a pause. Those are different questions, and only one of them is about traffic.

Redundancy is a word without a definition

New South Wales design guidance for vertical transportation asks a registered design practitioner to address redundancy during maintenance or repair outage. It does not define it. The National Construction Code does not define it either. There is no clause you can point at that says what redundancy means for a lift.

That gap has a practical effect. A design practitioner is asked to declare that a design accords with guidance material that contains a term nobody has defined, and the honest answer to what redundancy requires has, for some time, been that it needs to be settled at design stage.

The question that actually decides it

Strip away the drafting and it comes down to one thing. How many storeys is it reasonable to expect a resident with a medical condition, a pregnant woman, or a person with a disability to walk when the lift is out for repairs?

Once you put it that way, the answer is not really contested. It is not eight. It is not five. For a lot of people it is not two.

What the Code does give you

The NCC does set a hard marker that most people already know: where passenger lifts serve any storey above an effective height of 12 metres, at least one of the lifts serving each of those floors must accommodate a stretcher. Effective height of 12 metres is roughly four storeys above the entry level.

That threshold is doing more work than it appears to. It is the point at which the Code accepts that people can no longer reasonably be carried out by other means. It is a sensible place to draw the redundancy line as well: above 12 metres effective height, provide a second vertical transport option.

Apartment design guidance points the same direction, both in the caps it puts on how many apartments a single lift may serve above a certain height, and in the more recent language asking designers to consider access to an alternative lift when one is out of service. Read together, those are not saying more lifts move people faster. They are saying a single lift is a single point of failure for a building full of people who live there.

Why one lift is worse than the numbers suggest

A traffic study assumes the lift is running. Availability assumptions in a study are about minutes, not weeks. The outages that hurt residential buildings are not the ten-minute reset. They are the controller failure with an eight-week lead time on a board, the rope replacement that needs the shaft for a fortnight, the flood in the pit, the modernisation that overruns.

In a single-lift building, none of those are lift problems. They are habitability problems. Residents who cannot use stairs are effectively confined to their floor or to somewhere else entirely, and the body corporate is the one fielding the calls, arranging alternative accommodation, and occasionally defending a discrimination complaint.

Two lifts is not a luxury in that scenario. It is the difference between an inconvenience and a building that stops working.

What we recommend

Where the effective height of a building exceeds 12 metres, provide a minimum of two vertical transport options. Where the site or the budget genuinely will not carry a second shaft, the fallback is corridors that connect residents to a lift in another part of the building, designed in and documented, not assumed.

If you are an owner in a single-lift building that is already built, the redundancy decision was made for you, but the consequences are still manageable. Know the lead time on your controller boards and drive machine. Know whether spares are held locally or shipped. Ask your contractor what the realistic worst-case outage is for your specific equipment, in writing, and plan around that number rather than around an average. Put an outage protocol in place before you need it: who is notified, what alternative arrangements exist, and what the body corporate will fund.

A note for designers

Traffic planning tools tell you whether a lift selection will make a building work under normal operation. They are not redundancy calculations and they were never meant to be. Answering a redundancy question with a traffic study is answering a different question well.

The Australian Elevator Association canvassed this in its Industry Position Paper IPP-04, Redundancy, having sought clarification from a number of government bodies without getting a definition. The position we take here is our own, and it lands in the same place: above 12 metres effective height, two options.

General information only, not advice on a particular building. If you are weighing a second lift against other capital works, we can put numbers around what an outage actually costs you.