Street layout and density

17 Sep 2020

NOTE: The first version of the street layout and density calculator is available at this webpage. This notebook contains the source code.

Street layout and density calculator

Residential density appears to be a straightforward concept: some measure of housing (number of dwellings, building footprint, total floor area etc.) expressed as a ratio relative to land area. Increasing the size/volume of buildings as a mechanism for increasing density is well understood. Adding storeys or replacing small buildings with new ones with a bigger footprint are typical responses in the drive towards densification.

However, cities have a responsibility to manage the total area of land available to them. In simple terms this means the public spaces (including the highway) as well as the private land and the buildings built upon it. What is perhaps less well understood, particularly in cities that monitor density against plot or site area, is the role that the street network has to play in determining the relationship between urban form and overall density.

When ‘optimising land use’ (often a euphamism for increasing density) there is an interrelationship between the desired urban form, the street network and the resultant density. The relative permanence of the layout of the street network may explain the lack of focus on its role however, large scale urban regeneration projects and urban extensions are opportunities to revisit it.

This interactive web page is a first attempt at illustrating the relationship between the street network, urban form and density in two common types of urban form, the perimeter block and terrace/row housing. It demonstrates how two superficially similar building arrangements (abutting buildings aligned along the street) have fundamentally different relationships with the street network.

Some key points to note:

Increasing overall/gross density at a city scale is a simple matter of increasing the quantity of residential building relative to total land area. However it is worth remembering that at the city scale, the layout of the street network itself will impact both overall density and total capacity and that this may go unnoticed particularly if density is only monitored against the site or plot.

References