Size Shaft

A shaft is drawn early, at a size somebody remembered, and it is the hardest thing in the building to make bigger later. It is also sized by the wrong arithmetic: the sum of the services, when what it actually has to hold is the services plus the space to get them in and the space to reach them.

Inputs the command needs

1. The services, itemised: what each is, its outside dimension including insulation, and who supplied the figure.
2. Clearances: between services, to the enclosure, and any that come from code or from a manufacturer, each with its source.
3. Access: what has to be reached, how often, and from which side. Valves, dampers, cleanouts, meters, junction boxes.
4. The enclosure: rating required and construction proposed.
5. The shaft as drawn, if there is one.
6. Continuity: does the shaft run the full height, and does anything enter or leave at each floor?

Workflow

Step 1 — Read the schedule back and flag what is missing

List every service with its dimension and source. Anything without a dimension is not supplied and stays that way. Never substitute a typical size.

Flag services that are commonly forgotten in a shaft schedule and ask whether they are in the list: condensate, refrigerant, gas, fire protection standpipe and its valves, sprinkler mains, communications and low voltage, pneumatic tube, grease waste, vent stacks, and anything the specialist trades bring later.

Step 2 — Add up the section, not the sum

The shaft's dimension is a two-dimensional packing problem, not a total.

across      <service> + <clearance> + <service> + <clearance> + ... + <enclosure>
deep        <deepest service> + <clearance> + <enclosure>

Show the arithmetic in both directions with the source beside each term. State that the packing arrangement is an assumption unless you were given one, and that a different arrangement gives a different shaft.

Step 3 — Add installation space

The services do not appear in place. Ask, and report:

• In what order are they installed, and can each one get past the ones already there?
• Does anything arrive in a length that has to be manoeuvred inside the shaft?
• Is there a service that has to be installed from a floor other than where it runs?
• Is the shaft built around the services, or are they threaded into a completed shaft? These give different dimensions.

An assembly that fits in section and cannot be installed is the most common shaft failure.

Step 4 — Add maintenance access

For each item that has to be reached:

Item	Reached from	Access needed	Frequency

• Is access from inside the shaft, from an adjacent room, or through an access panel? Each has a different dimensional consequence.
• Is there a shaft that requires a person to enter it? That is a confined space and it carries requirements this command does not know; flag it.
• Does the access panel land in a corridor, a unit, a tenant space? Access through a leased space is an operational problem, not a detail.

Step 5 — Compare and report

	Required	Drawn	Difference
Across
Deep

Then:

• Every not supplied dimension, counted.
• Every assumption made about arrangement or installation.
• Where the shaft has to change size over its height, and what that does to the floors above and below.
• What is out of scope and named: rating and penetrations, smoke control, structural openings, and the plant rooms at each end.

Step 6 — Save, if asked

Ask whether to write the take-off to a file and where.

Rules

• Never supply a dimension or a clearance. Every term carries its source.
• Show the arithmetic in both directions, with the packing arrangement stated as an assumption.
• Add installation space and access space as separate additions, never as a percentage.
• Ask about the commonly forgotten services, every run.
• Flag any shaft requiring entry as a confined space question.
• Never size a service.

Anti-patterns

• Summing the service dimensions and calling that the shaft.
• Adding a percentage for clearance instead of the actual clearances.
• Recalling a typical duct or pipe size.
• Ignoring how the services get installed.
• Putting the access panel in a leased space without saying so.
• Sizing the shaft for the typical floor and not checking where it changes.
• Sizing the enclosure's rating here.