A Study On The Building Setback Control In Downtown Area Under The Need Of Street Vitality

Street setback,a mandatory buffer between the public domain and building frontage,has been practiced widely across contemporary Chinese cities.Originally conceived for aesthetic hygiene,safety,and road-widening purposes and borrowed from American zoning practices decades ago,setback rules are embedded in the Chinese National Regulatory Planning System and superimposed on most streets regardless of the actual programs and urban context.The rigidity of the setback rules is accused of having caused many ills of the Chinese streetscape,i.e.missing street facade,lack of human scale,and loss of vitality.The setback area,often fenced off for safety and maintenance convenience,or occupied by car parking,becomes a leftover space where legitimate building activities are barred,while “creative” yet quasi-legal ones were common place yet not always desirable.Systematic studies on street vitality and setback are rare.Urban planning literature typically focus on the setback distance itself;few questioned the purposes and legitimacy of the setback rules in contemporary context.Rarely are there discussions of a more flexible setback rules allowing more varieties for specific context.Question rise as to what extend are setback rules still appropriate existing conditions in Chinese Cities and how to improve the rule system to achieve street vitality?Firstly,the thesis explore the origin of setback rules,the relationship between urban demand and rules,and its development in China,and find out that: 1)the existing setback rules came from the Industrial Revolution for urban congestion resolution and show strong problemtargeted oritentation and low-density residential characteristic,it's not appropriate to be used in everywhere,expecially in downtown;2)the existing rule system is car-oriented,which is contradiction with the goal to achieve street vitalty,and the problems caused by rule setting are even detrimental to street vitality.Secondly,positive elements of vibrant setback area and rules are summarized from vitality-oriented rules in urban,street and project level,which under three main advanced concpect—public-private integration,three-dimension and form detailed control.And the analysis shows that 1)wide street setback(over 20m)is negatively correlated with vitality;2)accessible setback areas,those without fences,are positively linked to vitality;3)street furniture and public arts are conducive to vitality,car parking or grass turf does the opposite.Finally,the thesis concludes with a speculative proposal for setback rule system optimization which focus on attribute sysem,including setback distance,setback line definition,programs,construction and street wall design.Then policy scenarios are discussed under which the setback area is 1)left with the private owners to build according a guideline;2)taken over by the public sector and redevelop;3)retrofitted under a public-private-partnership scheme.And the last are the depth of the content and the requirement to depth of different levels of rules.