MEP / Plumbing / Fire Shaft Sizing
Vertical riser shafts are set by the core layout very early and are painful to enlarge later. These indicative sizes help you reserve enough core space for each service group before the detailed riser design.
| Shaft | Carries | Indicative clear size |
|---|---|---|
| Electrical riser | Bus-ducts / cable risers, LT & ELV (segregated) | ~1.0–2.0 m² per riser group |
| Plumbing/PHE shaft | Water supply, soil, waste & vent stacks | ~0.6–1.2 m wide, depth by stack count |
| Fire-service riser shaft | Wet-riser, sprinkler main, hydrant standpipe | Sized to risers + valve access |
| HVAC shaft | Supply, return, fresh-air & exhaust ducts | Largest where vertical ducts run |
Reserve separate, stacked, accessible shafts for electrical, plumbing, fire and HVAC in the core — keep electrical segregated from wet services, and allow door/access to valves and dampers on each floor.
Verify — Rule of thumb only. Shaft sizes follow the actual riser count and diameters, fire-compartmentation and access requirements. Confirm against the MEP riser schedule, the code edition and local requirements adopted for the project. These allowances are not statutory minimums.
How to size an MEP shaft from the actual services
An MEP shaft is a vertical space reserved for building services. Its usable size comes from the equipment and pipe arrangement, supports, insulation, access and fire separation. A floor-area allowance alone cannot show whether a valve can be reached or a pipe can be replaced.
Use the indicative table above to reserve space during concept design. Before fixing the core or slab openings, replace that allowance with a dimensioned plan and section for each shaft type.
- List each service. Record the number and outside dimensions of pipes, ducts, cable trays or bus ducts. Include insulation, flanges, fittings, supports and any agreed future provision. Mark unselected equipment and unconfirmed sizes.
- Draw the arrangement. Show the services against the finished internal shaft faces. Include beams, wall thickness, offsets and branch connections; a shaft that fits on a typical floor may fail at a transfer floor.
- Check access. Locate doors and panels against the valves, dampers, cleanouts and joints they serve. Show how a person reaches the component and how the largest replaceable item comes out.
- Coordinate separation and penetrations. Agree service segregation, compartmentation and the penetration details with the electrical, fire, architectural and structural teams. Record the applicable code edition and authority requirements.
- Issue one coordinated revision. Put the shaft identifier, clear dimensions, opening sizes, access side and unresolved items on the drawings. Check the same revision at each floor before construction.
Why the same shaft area can produce different results
A 1.0 m × 1.0 m shaft and a 0.5 m × 2.0 m shaft both have an area of 1 m². They do not provide the same arrangement or access. A fitting may fit across one width and obstruct another; the access door may face the wrong side. This is a geometry example, not a recommended shaft size.
On the coordinated drawing, distinguish the structural opening from the finished clear space. Wall finishes, fire protection, brackets and insulation all consume space. Checking only the pipe centre lines can hide that loss.
PHE shaft, fire-service riser and firefighting shaft
- PHE shaft: space for the agreed water-supply, soil, waste, vent and rainwater services. Start with the PHE scope definition and the riser schedule.
- Fire-service riser shaft: space for the fire-water risers and their associated access. The fire-system designer determines its arrangement.
- Firefighting shaft: do not use this term as a synonym for a pipe duct. The protected access arrangement for firefighters must be defined separately in the building's fire strategy and approved drawings.
Can electrical and wet services share a shaft?
Do not allocate them to a common power-cable duct just because there is spare space. Regulation 38(3)(iii) of the CEA Safety Regulations, 2023 prohibits other service pipes and cables in ducts provided for power cables and requires fire barriers at floor crossings. Regulation 38 covers multi-storeyed buildings above fifteen metres and specified other premises. Check the clause's scope and the project requirements before agreeing an arrangement.
Source: CEA Safety Regulations, 2023, Regulation 38, Gazette text hosted by the Directorate General of Mines Safety (PDF). This source supports the electrical segregation point; it does not prescribe the rule-of-thumb shaft dimensions above.
What to bring to a shaft coordination review
Provide the current architectural core plans, building sections, structural framing and opening constraints, service riser schedules, equipment dimensions and the fire strategy. Include the access and replacement requirements, the project stage and a list of missing information. The review can then identify which dimensions are supported and which still depend on a design decision.
For the wider package, see plumbing and public health engineering, fire-fighting riser and sprinkler installation, HT/LT electrical works, bus ducts and cable risers and MEP design coordination. Shaft dimensions remain project-specific; this guide is a planning method, not a construction release.
Want this coordinated against your structure?
Send us your schematic and we'll mark up a coordinated services section — so your ceiling height and shafts survive detailed design. The other clearance guides, checklists and specification libraries are on the architects' hub.