How to Plan Elevator Shaft, Cabin, Pit, and Overhead Dimensions

On most projects the lift well is designed before anyone has decided which lift will go into it. The core is drawn at concept stage, cast a few months later, and the elevator itself is bought at tender. Almost everything that goes wrong with a shaft lives in that gap.

By the time a manufacturer first sees the building, the well is concrete. Whatever it can accommodate is what the building gets, and it will keep getting it for the next thirty or forty years.

Shaft sizing is therefore not a procurement detail to be settled once a supplier is appointed. It is a planning decision, taken early and with incomplete information, that quietly fixes how a building will work for the rest of its life. The point of this guide is to help you take it deliberately.

Six things separate a well that was planned from one that merely happened:

• Why the well gets decided before the lift does
• What a wrong well costs, depending on when you find out
• What cabin size is really deciding
• Why pit and overhead are the two that bite
• Why naming the standard is part of the plan
• What has to be locked before the slab, and what can wait

Let's start with why the sequence works against you.

Why the Well Gets Decided Before the Lift

The order in which a building comes together is the root of the problem. The architect has to reserve a well early, because the core affects the floor plate, the lobby, and the structural grid. The structural engineer commits to pit level and slab levels soon after. The owner settles capacity, speed, and finishes later, often much later. The elevator manufacturer arrives last and inherits all of it.

None of that is anyone's mistake. The core cannot wait for a supplier to be appointed, because the rest of the building depends on it. Space has to be reserved before the decision that would justify it has been taken.

What follows from that is the important part. If the well must be sized before the lift is chosen, the planning question is not "what size is the lift" but "what range of lifts must this well still be able to accept". Those are different questions, and they produce different cores.

It is also why "we will confirm it with the vendor later" is not a plan. A manufacturer can confirm what fits a well that already exists; they cannot give space back. Confirming late converts a design decision into an acceptance of whatever the concrete happens to allow.

What a Wrong Well Costs Depends on When You Find Out

The same error carries four completely different prices, and the only variable is how late it surfaces.

• At concept stage — the well is still a line on a drawing, and correcting it costs a revision and nothing more.
• During detailed design — the fix ripples into structural coordination: a beam moved, a lobby redrawn, a service route diverted. Expensive in time rather than money.
• After the slab is cast — now it is civil work. Breaking out and recasting a pit means structural review, fresh waterproofing, and a programme delay that everyone on site feels.
• After tender — usually it is not fixed at all. The building accepts a smaller cabin, a slower lift, or a product nobody specified, and carries that decision for the life of the asset.

Notice what actually changes across that list. The error itself never gets any larger. What shrinks is the number of ways you are still allowed to deal with it. A well that is slightly tight is trivial while the drawing is soft, and permanent once it is concrete.

That asymmetry is the entire argument for taking shaft planning seriously at the earliest possible stage. It is not that early decisions are more accurate — they are made with less information, so they are usually less accurate. It is that early decisions are cheap to revise and late ones are not.

Cabin Size Is a Service Decision, Not a Measurement

A cabin is usually discussed as a dimension, which makes it sound like a technical detail for somebody else to resolve. It is better understood as a statement about what the building will be able to do.

• How many people travel per trip, which decides how long the queue is at the morning peak
• Whether a stretcher and attendants can be carried, which decides how the building copes with a medical emergency
• Whether a loaded trolley or pallet fits, which decides whether goods move by lift or by staircase
• Whether a wheelchair can enter, turn, and leave, which decides whether the building is genuinely accessible

Every one of those is a service level rather than a measurement, and every one of them is settled permanently by the size of a well that was reserved years earlier.

When the cabin is chosen to fit the core, instead of the core being sized to fit the cabin, the building's service level has effectively been set by a civil drawing. That is the wrong way round, and it is very common.

It also helps to know that capacity does not simply scale a rectangle. A larger car is not always a proportionally bigger version of a smaller one, because passengers are served better standing across the width of a car than queueing down its depth. As capacity rises, cabins tend to become wider rather than uniformly larger. The practical consequence is that deepening a core "to be safe" can buy nothing at all, if the next capacity up needs width instead. Reserving space generously is sound planning; reserving it in the wrong direction only looks like it.

Pit and Overhead Are the Two That Bite

Shaft width and depth get attention because they appear on every floor plan. Pit depth and overhead are the more dangerous pair, for three reasons that compound one another.

First, they live in the section rather than the plan, and sections are reviewed by fewer people. A well that is correct on every floor plate can still be wrong at the top and the bottom of the building.

Second, they are not driven by capacity. They are driven by rated speed, because a faster car needs more room to decelerate below the lowest landing and above the highest. Capacity sets the cabin, and therefore the plan. Speed sets the pit and the overhead, and therefore the section.

Third, they are the two figures buried in concrete. The pit is excavation and waterproofing below the lowest slab. The overhead is the top of the structure, and sometimes a machine room above it. These are the dimensions that cannot be recovered without demolition.

Put those together and a familiar failure appears. Teams fix capacity early, because it feels like the significant decision, and leave speed to be confirmed later, because it feels like a refinement. But speed governs the two dimensions that are hardest to change. The refinement ends up dictating the excavation.

The planning response is straightforward: detail the pit and the overhead for the fastest speed the building might plausibly want, not the speed on the first sketch. Extra depth agreed at excavation is comparatively cheap. The same depth after casting is a demolition job. Where a tall building might later want a faster lift, or where an owner is likely to upgrade at modernisation, that headroom is worth buying at the only moment it is affordable.

Travel height is a separate matter that is easily confused with these. The distance from the lowest to the highest landing does not change the shaft, the pit, or the overhead. It determines which products can serve the building at all, so treat it as a question about the lift rather than about the civil works.

"An Eight-Person Lift" Is Not a Specification

A drawing that calls for an eight-passenger lift looks unambiguous. It is not.

Standards assume a different mass per person and derive rated load in different ways. Under IS, the load follows directly from the person count. Under EN, it follows from a higher assumed mass and is also capped by a maximum permitted car area, so the car cannot be oversized relative to its rating. Under ASME the logic runs the other way around: the rating comes from the platform area, and a person count is inferred from it afterwards.

The same nominal lift is therefore a different car, with a different rated load, in a differently proportioned well, depending on which standard the project works to — and one of those standards does not really deal in person counts at all.

So a drawing that names a person count without naming a standard has left a decision open, and that decision will be closed by whoever prices the job. A supplier is not the right party to settle which code a building is certified against.

Name the standard on the drawing, and use the one the installation will actually be certified against rather than the one a reference detail happened to come from. Mixing them — a cabin from one, a pit from another — produces a well that satisfies neither the inspection nor the product eventually quoted.

Local lift rules then sit on top of all of this. They may set a minimum number of lifts, require a fireman's lift, or cap travel time from the lowest floor to the top. Those are additional obligations rather than substitutes for getting the well right.

What to Lock Before the Slab, and What Can Wait

Not every elevator decision has to be early. Confusing the two categories causes both kinds of failure: cores frozen on guesswork, and cores left open until the concrete decides on everyone's behalf.

These belong before the core is cast, because they change the structure:

• The type of lift — a passenger car, a bed lift, a goods lift, and a small service lift are different problems with different wells
• The standard the installation will be certified against
• The well footprint, sized for the largest capacity the building might reasonably need
• Pit depth and overhead, sized for the upper end of the plausible speed range
• Which side the doors open, and whether any landing needs a through-car arrangement

These can safely wait, because none of them change the well:

• Cabin interior, flooring, and wall finishes
• Fixtures, signalling, and display types
• Control features, access control, and remote monitoring
• Most comfort and cosmetic specifications

Capacity and speed cause the most trouble, because they look like procurement questions and behave like civil ones. Neither has to be fixed precisely at concept stage, but the plausible range does have to be agreed — and the well detailed for the top of it.

That is the discipline in a sentence: plan the envelope, not the product. You are not specifying a lift at concept stage. You are reserving space for a decision that has not been taken yet.

Reserve Space for the Decision You Have Not Made

A shaft is planned well when it stops being interesting. Nobody notices a core that comfortably accepted the lift the building turned out to need. A poorly planned one gets noticed every day — as a cabin too small for the queue, a car too slow for the tower, or a stretcher that will not fit.

The order that works is type, then standard, then the capacity range, then the speed range, with the well detailed for the generous end of both. The generous end costs almost nothing while the drawing is still soft.

For indicative figures at concept stage, tools/shaft-sizing-calculator will size a well from a capacity and speed, or check what still fits a core you have already measured, and tools/elevator-dimensions sets out the underlying reference tables with a PDF you can attach to a drawing set.

Shaft size is only part of the brief. Capacity, features, and occupancy belong to the specification, and blog/specification-of-passenger-elevator covers that ground for passenger lifts. How many lifts a building needs is a traffic question, and blog/advisors-for-lifts-in-new-projects works through who should answer it. Once the well is settled, blog/which-elevator-does-your-building-need helps shortlist a product that fits it.

If you would rather have the envelope checked against a real project than estimated from tables, send your drawings and building details to the Blue Star Elevators engineering team through enquiry — we will confirm the shaft, pit, and overhead your intended specification needs, while those figures are still cheap to change.