What are Neighbourhood Units?
When designing New Towns or other large scale masterplans, a popular approach is to subdivide the masterplan into small 'neighbourhood units', sometimes called 'communities' or 'urban villages'.
Each Neighbourhood can be described as a circular blob with a diameter and an average density.
The diameter can be measured in metres, but it can be more useful to use 'Mins' Walk Across', as this is a more meaningful measure of distance to residents.
How many dwellings are in one Neighbourhood Unit?
This depends on its density and size. If the Neighbourhood is circular, this graph shows how many dwellings can be achieved at different densities and different sizes.
For example, if a new development needs to be 10 mins' walk across, then the graph shows that an average density of 30dph across the development will yield about 1000 dwellings, while an average of 40 will yield about 2000.
(This is obviously not an exact science, as the shape of the Neighbourhood Units will vary according to local constraints, and is unlikely to be exactly circular.)
NB. In the graph, the Densities are Gross (or 'Neighbourhood' or 'City') Densities. Normally it is Net Residential Density which is discussed and negotiated. Net Densities exclude major roads, hospitals, schools, playing fields etc in their calculation. Although areas of housing may have a Net density of 30 dw/ha, the overall Gross density of the Neighbourhood may only be 10dph or so.
What sort of services can each Neighbourhood Unit support?
This depends on a complex range of factors, but the number of dwellings is often a useful measure of what can be supported.
Let's say that each Neighbourhood Unit needs a service, such as a local shop, which needs approximately 2,000 dwellings to support it.
Going back to the graph, a horizontal line can be drawn at this number.
The graph tells us that a range of options are available to achieve 2,000 dwellings.
It could be 10 mins' walk across, but then an average density of 40dw/ha would be needed. This is a high Gross density, and probably only appropriate in a town centre location. Alternatively it could be 15 mins' walk across, with an average density of 20dw/ha.
Of course most developments are far more complex than this, but the graph is useful for quickly estimating numbers.
Our city modelling technology - CityCAD - will make analysis of complex masterplans with many different densities much easier at the conceptual stage.
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