I’ve been away for a week, with limited online access, and while away happened into Bristol’s Architecture Centre, which was hosting a small but rich exhibition on ‘Suburban Futures’, and almost completely unadvertised, at least from the street. 86% of the population of England live in suburbs, so making them sustainable is a valuable project. Increasing density is necessary – but benefits start to follow from this, in terms of the quality of community life.

Pulling together some threads from the exhibition, the important metrics are dwellings per hectare [10,000 sq. metres, or 2.47 acres], or dph, and people per dwelling [ppd]. The 1900s terrace manages 90 dph; the Georgian terrace 50 dph; the 1980s estate 35 dph; and the 1930s semi 25 dph. 25 dph is also the English suburban average at the moment, if I read the exhibition data correctly, and also the average for new build suburbia.

Some specific research done by the University of the West of England on “suburban embedding” as (part of the multi-university SOLUTIONS programme) looked at a low density (16 dph) suburb from 1947, when there were 3 people per house, to 2.25 people per house now (or around 37 people per hectare). At these densities, the community becomes so spread out that car dependency is all but inevitable.

And there are some useful calculations by Barton, Grant, and Guise (from their Shaping Neighbourhoods study) on how many people it takes to support different community assets:

  • 4,000 people for a primary school
  • 1,000 people for a local shop
  • 6,000 people for a pub (seems high to me)
  • 5,000 people for a post office
  • 4,000 people for a community centre (seems low, but I suppose it depends on how you define a community centre).

In other words, the UWE’s study site, mentioned above, would be sprawling across 30 hectares, or 75 acres – or 45 football pitches, if it makes it easier to imagine – before it supported a single local shop.

One relevant study here is by the architects’ practice MacCormac, Jamieson, Pritchard (MJP). In ‘Sustainable Suburbia‘, they looked at five different types of suburban plan, all of which were designed around a settlement of 5,000 dwellings (around 11,000 people). At 50 dph, they could still design for three-bedroomed houses, with gardens and off-street parking. Above this, different types of smaller housing, such as maisonettes, came into the mix. From the community perspective, there started to be significant gains above 50 dph; because less space is now taken up by housing, land is made available for shared benefits such as shops and employment.

At this point it’s worth mentioning URBED’s Tomorrow’s Suburbs toolkit, written for the Mayor of London, which lists seven objectives which need to be achieved in a sustainable suburb:

  1. Reinforcing the role of local centres;
  2. Making new development sustainable;
  3. Improving the existing housing stock
  4. Promoting alternatives to travel by car
  5. Improving environmental sustainability
  6. Protecting and promoting suburban employment
  7. Improving design and the public realm.

So as density heads above 50+dph, it’s easier to tick off the objectives. There are also gains in terms of social mix; more mixed housing leads to more diverse demographics.

Part of the UWE SOLUTIONS project mentioned above is about envisioing how to transform the 16dph suburb by 2031. Part of this involves ‘infilling’ – effectively creating terraces. An area which currently has 66 dwellings could, they reckon, take another 44. But despite this, there’s also scope to create new shared, and safe, public spaces, partly by reclaiming for other uses space currently given over to roads for car access. Thus is the process described by the architect Leon Krier as “the urbanisation of suburbia, the redevelopment of sprawl”.

It’s also worth mentioning building costs. There are government guidelines about constructing at a building cost of £60,000 per unit. Proctor and Matthews prefabricated design is a modular house at this price. It’s being built at 52 dph in Harlow, according to the exhibition, and is described as a way of achieving higher densities at low rise while delivering houses suitable for families. They explain the rationale here (opens in pdf). It’s also worth looking at a Building Design article on why prefabricated construction isn’t more widespread.

The exhibition, sadly, has only a week to run (to June 8th) – it deserves further exposure, and would fit nicely in RIBA’s mezzanine space.

Update: The Campaign for Rural England has just released a report called The Proximity Principle – subtitled “Why we are living too far apart”, which addresses similar issues of density. To quote from its website:

“Our report finds that proximity encourages community interaction, makes public transport, local services and environmental initiatives more viable, and drives creativity – a key component of a successful economy.”

The Proximity Principle is also downloadable in pdf from here. See also my post on a Forum for the Future event on suburban sustainability as well.

Other related posts: DOTT 07 – sustainable design for communities and Making the Transition locally.