Buildings could be constructed far taller than most cities permit. The binding limits are regulatory and economic, and they appear as thresholds where cost jumps rather than as gradual increases.
Zoning converts height into floor area
Many systems control development by limiting total floor area relative to plot size rather than by stating a height, leaving the developer to distribute that area.
A tall slim tower and a low broad block can therefore be equally permissible, and the choice between them turns on site shape, daylight and construction cost.
Where a specific height cap exists, it usually protects a view, an approach path or the setting of a landmark, and such caps are defined geographically rather than uniformly.
Daylight rules constrain massing
Regulations in many cities require that neighbouring windows retain a defined amount of daylight, and that public spaces are not overshadowed beyond stated limits.
Compliance is demonstrated by modelling the proposal against the surrounding built form, and failure requires the mass to be reshaped rather than merely reduced.
Setback requirements arise from the same logic, which is why older towers step inward as they rise while newer ones on cleared sites do not need to.
Fire strategy sets hard thresholds
Above defined heights, buildings must provide additional protected stairs, firefighting lifts, sprinkler systems and refuge floors, and requirements escalate at further thresholds.
Each escalation consumes floor area that cannot be sold or let, so the usable proportion of the building falls as height rises.
The economics therefore favour stopping just below a threshold rather than exceeding it slightly, which is why buildings cluster at particular heights within a city.
Structure and services grow faster than area
Wind load rises steeply with height, and resisting it requires progressively more structure, which occupies space and adds foundation cost.
Lifts consume floor plate on every level they serve, so a tall building devotes an increasing share of its area to moving people vertically rather than housing them.
Above a point, each additional floor adds less lettable area than it costs to build, and that point is reached far below any engineering limit.
Local politics decides many cases
Height is highly visible, so proposals attract objection on grounds of character, precedent and views, and decisions are made by bodies answerable to residents.
Cities that want taller buildings tend to designate specific zones for them, which concentrates the argument geographically instead of repeating it site by site.
Rules differ enormously between jurisdictions and change with political cycles, so a form that is routine in one city may be effectively impossible in another.