Proactive vs. reactive urbanism: decoding the regulatory DNA of ultra-tall buildings in Chicago and Dubai

This paper examines the spatial, structural, and regulatory evolution of ultra-tall buildings through an urban morphology and institutional lens, expanding the urban planning discourse beyond static volumetric parameters and iconic form toward dynamic, functional governance frameworks. While traditional urban planning relies on prescriptive zoning ordinances - defined here as Micro-Controllers (MC)- to manage incremental, localized growth, the extreme verticality of the ultra-tall introduces a “hyper-element” that transcends these static limits by merging horizontal plots and internalizing public infrastructure networks. Consequently, municipal authorities deploy large-scale, discretionary, and negotiated legislative and financial instruments, termed here Macro-Controllers (MA), to manage this intensification. Utilizing a comparative perspective analysis of Chicago’s market-driven development and Dubai’s state-backed expansion, this paper maps how these instruments function as “epigenetic triggers” that modify the expression of a city’s baseline regulatory code, ‘Regulatory DNA’. The analysis reveals a fundamental duality in vertical intensification: Chicago mainly operates on a Reactive model that deploys macro-level filters such as Planned Developments (PD), Tax Increment Financing (TIF), floor area ratio (FAR), and Air Rights transfer, to negotiate density into a path-dependent historic grain, whereas Dubai utilizes a Proactive model where the vertical hyper-element acts as a speculative nodal catalyst to manufacture real-estate value ex-nihilo. Ultimately, this paper establishes an evaluative framework for ultra-tall development, offering scholars a conceptual model for decoding extreme verticality, while equipping planners and policymakers with actionable insights to regulate hyper-elements as high-performance, functionally integrated urban organs. Regulatory DNA: The spatial, structural, and regulatory code of a city, comprising both physical typologies (streets, plots, blocks) and the legal constraints that govern their reproduction. Hyper-Element: An urban intervention of such extreme scale and programmatic density that it transcends standard property boundaries, internalizes public infrastructure, and fundamentally alters the local urban morphology. Micro-Controllers (MC): Prescriptive, static, “by-right” zoning regulations (e.g., standard setbacks, height caps, lot coverage ratios, height-to-street proportions) designed as a bulk and density controller to maintain predictable, incremental growth across a typical urban grain. Macro-Controllers (MA): Large-scale, discretionary legislative and financial mechanisms (e.g., Planned Developments, Integrated Master Plans, TIF) deployed to negotiate, accelerate, or filter the spatial mutation caused by a hyper-element.