The existence of a substantial and compact residential and business community within easy walking distance of an urban or neighbourhood centre is the principal platform for sustainable development. This catchment (at least 5000 people for a typical, sustainable neighbourhood) can support a bus route and a variety of shops and services, and can attract other commercial investment. It requires an average neighbourhood density of at least 65 dwellings per hectare with higher density towards the centre of the neighbourhood (or town centre, transport corridor etc.). This allows for lower densities towards the margins of the neighbourhood.

Of course, many sites suitable for development are located within existing neighbourhoods that incorporate a range of densities – and these may not combine to an average density of 65 dwellings per hectare. Indeed, this is the case for the majority of urban places in Essex.

In contrast, new large urban extensions can be easily designed to achieve this density – but applying it universally across a development would not produce the ideal variety of housing stock or an attractively diverse environment. In such situations, where there is the scope to construct new urban fabric based upon the many sustainable urban design principles contained within this guide, density should become a by-product of the process rather than its driving force.

This guidance requires a range of minimum development densities that are applicable to the different sustainable development types. The most compact development is required in the most sustainable locations, with a progressively reducing minimum density beyond these locations. There is no upper density limit within these specific areas. However, the Context Appraisal will help designers and Local Authorities to determine the appropriate density above the minimum base density prescribed in the guidance. These decisions need to be informed, in part, by the accessibility and quantity of existing local amenities (such as shops, green spaces and schools) that are so vital for higher densities to function. Some of these amenities can be established or improved over time either via the process of new development or through the management of market forces. Nevertheless, within larger developments (of 50 hectares or more) it is essential that these amenities are in place at the beginning of the development of the new community.

Where large urban infill or sustainable urban extensions are proposed, it is important to ensure that a range of development types and densities is accommodated, as this will enable a variety of living and working environments to evolve. The spatial model of the urban centre and neighbourhood should be employed to ensure a varied urban pattern across the site. Development densities will be at their highest towards the centre of these new units of sustainability but reduce towards their boundaries, enabling space for detached houses with gardens at the fringe but still within convenient walking distance of shops, services and public transport. The target population for these developments will be 5000 people per unit of sustainability.

Describing density by habitable rooms, plot ratios or people per hectare can provide a textured picture of a development and is particularly suitable for mixed-use scenarios. However, the terms are not widely used by central government or district councils and therefore the definition of density within this document has been expressed as dwellings per hectare.

Densities are measured in relation to the net site area which includes:

• Private and communal open space
• Internal streets
• Multi-functional public space intended principally for the benefit and enjoyment of occupiers of the development
• Non-residential uses within a mixed-use building that also contains residential accommodation

Net density excludes public open space, the streets along the boundary of the site that serve a wider area and any non-residential uses that are not located above or below residential accommodation.

It is understood that there can arise a conflict between two of the requirements outlined in this guide: the need for developers to achieve minimum densities for development and the need for them to accommodate mixed-use development. Achieving minimum density thresholds using the density measure for residential development (dwellings per hectare) alone would be incompatible with encouraging a substantial provision of mixed-use development. The calculations should therefore take account of the space taken up by non-residential uses within mixed-use buildings.

To this end, developers may factor in an allowance of one dwelling per 75 sq m of non-residential use. Note however that the only non-residential space that should be factored into the density calculation is that contained within a mixed-use building that includes residential use. A typical calculation is shown below. 

Sample calculation
No. of apartments: 210 No. of houses: 25 Non-residential space with residential use above: Community use (150 ÷ 75 sq m ) = 2 Commercial use (3750 ÷ 75 sq m) = 50 Total 287 Net site area = 2.5 ha Development density = 115 dwellings per hectare