Lift Sizing Calculator - Part M Passenger Lift Car & Shaft Dimensions

Approved Document M Vol 2 (para 3.34) requires a minimum lift car internal size of 1100mm wide × 1400mm deep for wheelchair access in new buildings (BS EN 81-70:2021+A1:2022 Type 2). The car door must be at least 900mm clear opening width. BS 8300-2:2018 references the same accessible-car minimum. For busy or public buildings Part M para 3.29 recommends a larger 2000mm wide × 1400mm deep car (BS EN 81-70 Type 5, 1275kg, 1100mm door) so a wheelchair user can turn through 180°. Where stretcher access is needed a deeper Type 3 car of 1100mm × 2100mm is used.

Shaft dimensions are calculated from the car size plus clearances for the guide rails, counterweight, door mechanism, and safety equipment. Typically, the shaft is 400-500mm wider than the car (200-250mm clearance each side) and 500-550mm deeper (200mm for the door mechanism plus 300-350mm for the counterweight). The exact dimensions vary by manufacturer, so these are indicative for early design stages.

Approved Document B and BS 9999 require a firefighting lift where a building has a floor more than 18m above (or more than 10m below) fire service vehicle access level. Firefighting lifts must comply with BS EN 81-72:2020 and BS EN 81-20:2020, with a secondary (independent) power supply and firefighter controls on a separate circuit. The minimum firefighting-lift car under BS EN 81-72:2020 is 630kg / 8-person at 1100mm × 1400mm with an 800mm clear door. The larger 1000kg / 1100mm × 2100mm car is only required where the firefighting lift also serves as an evacuation lift for a stretcher or bed.

BS EN 81-20:2020 does not specify a single pit depth — it sets the bottom refuge space (the safe clearance for a person under the car at full overtravel), from which the pit depth is derived together with the buffer stroke and rated speed. Typical worked figures are around 1200mm for lifts up to 1.0 m/s, 1400mm around 1.6 m/s, and 1600mm or more for higher speeds, but these vary by manufacturer, so treat them as indicative. Reduced-pit solutions using special buffers and safety gear are available but must be approved by the notified body.

The number of lifts depends on building population, floors served, and acceptable waiting times. BCO Guide to Specification recommends average waiting times under 25 seconds for commercial offices. A traffic analysis (using tools like CIBSE Guide D) is recommended. As a rule of thumb, one 13-person lift serves approximately 200 people in a 6-storey building with acceptable wait times.