Wong (2017) elaborates the legal origins of HK building codes on setting back the top stories of buildings (light angle or tapered buildings) from the UK:
“The English Public Health Act of 1875 regulated building heights to allow the sun light to reach the streets by aiming for a maximum diagonal of 45 degrees between the building line (at ground level) on one side of a new street and the skyline formed by the edge of the roof on the other side. The angle is not explicitly mentioned but implied in a set of bylaws stating:
If the height of such building be 15 feet, he shall cause such distance (width of open space) to be 15 feet at the least.
If the height of such building be 25 feet, he shall cause such distance to be 20 feet at the lease.
If the height of such building be 35 feet, or exceed 35 feet, he shall cause such distance to be 25 feet at the least.
In these cases, the implied angle varied from 45 degrees to 54.5 degrees.
The light-angle terminology in degrees was employed in the English Housing Act of 1890 and the London Building Act of 1894. They mention the use of a 63.5-degree angle for backyards, and the calculation to be decided from the center line of the open space between two rows of buildings.” (p. 196)
Hong Kong started enforcing light-angle since the Buildings Ordinance of 1903, after a series of epidemic outbreaks in the city. “It specified the same 63.5-degree rule for regulating building heights.” (p. 196)
Even though it specified light-angle, but normally it regulated building height, rather than a set-back of the top stories of buildings. For example, “land leased from the Crown after 1903 “the respective height of the building could not exceed 1.25 or 1.0 times the width of the street… Buildings constructed under these limitations reached an average height of 3.6 stories with a low standard deviation of 0.8 stories” (p. 197)
“In 1955, the situation was altered radically with a new ordinance permitting considerably higher structures. The height of the main wall facing the street was not to exceed 76 degrees from the horizontal, greater heights permitted for corner and ‘island’ lots. The average height of buildings constructed in the period 1960-1962 rose to 9.39 stories.” (p. 197-198)
Finally, it is the first Building (Planning) Regulation introducing plot ratio control in 1962 that triggered set back of the top stories of buildings. As we have discussed in ecyY blog before, because of the objections of landlord, the government finally granted a grace period to implement the new regulations of plot ratio control until Jan 1, 1966. “Landlords used all means to submit building plans ahead of the deadline. The plans submitted during this period also introduced the practice of set-back profusely – which was the best proof of the rush to build. Under the ruling of a 76-degree angle from the horizontal, a landlord was able to increase floor space if he or she chose to set back the top stories in steps while observing that angle for the hypotenuse.
For the set-back, the cost of construction is exceptionally high because of the irregular structural framing and the decreasing area for each of the set-back floors. But it was worth doing for the landlord because this was a now-or-never decision.” (p. 199)
In other words, Wong (2017) opined that it is the last chance of volume control of development intensity that triggered the set-back of the top stories of buildings, because if the landlords did not build, the benefits would be forfeited.
Yet, interestingly, due to the economic recession and the housing bust from mid-1965 to late 1969 deterred from building more tapered buildings. Ironically, he suspects the rush of construction might have triggered the bank runs and the economic recession, and perhaps even contributed to the riots as the living conditions of the people evicted from their homes worsened.” (p.199)
Wong, Richard (2017) Fixing Inequality in Hong Kong, A Friedman Lecture Fund Monograph, Hong Kong: Hong Kong University Press.
Wong, Richard (2015) Building Codes and Postwar Reconstruction in Hong Kong, http://wangyujian.hku.hk/?p=6100&lang=en