Stairs are the dominant cost, not the floors
In a narrow four-level building, stair treads, risers, handrails and landings can take as long as the occupied rooms. They are also the most visible surface, since everyone in the building uses them several times a day. Pricing by floor area consistently underestimates these buildings, which is why an area-based quote for a terrace usually turns into a variation within a quarter.
Equipment movement compounds it. Carrying a vacuum and a bucket up and down four levels is slow, and the practical response is either equipment stationed on more than one level or a sequence designed to minimise trips. Both need deciding in advance. Leaving it to the individual on shift means the time is lost every visit rather than once.
