It’s difficult to generalise about suburbs. The classic British image of cul-de-sacs lined with parked cars doesn’t cover it – Notting Hill in central London was built as a suburb, and many Parisian suburbs are high rise and have the feel of the inner city.

So, as Richard Rogers reminded us last Wednesday night at Forum For The Future’s Ahead of the Agenda seminar ‘Can suburbs make a comeback?’, it’s easier to talk about density. Suburbs tend to be less densely populated – between 2 and 28 people per hectare according to Southampton University.

Given that over 80% of Brits live in suburbs – with similar proportions in Europe and North America – they are strangely absent from talk of sustainable future cities. We’re more used to visions of super-urban, high-density, mixed-use, bike-able or walkable metropolises, with the odd monorail thrown in. It’s not easy to see how that vision can be superimposed on a settlement pattern that makes a virtue of private (not public) space and since the 1930s has largely been predicated on ownership of a car.

But one way or another, something has got to change. For a start, a bit of in-filling wouldn’t go amiss. Increase the population density of suburbs by just four people per hectare and you could accommodate all of the expected population growth in the UK for the next 40 years without having to touch a single green field*. That’s just one or two more houses in every suburban hectare.

And we could use suburbs to make towns and cities more resilient in coping with future stresses. Droughts, flooding, power failure, food shortages, pandemic…any number of future challenges could stretch a city’s infrastructure to breaking point. Suburbs could act as ‘redundancy’ in the city’s system, providing the spare capacity that might make a city stronger at times of crisis. In practical terms this could mean siting more allotments and market gardens in suburbs, as well as micro-reservoirs, water meadows or marsh for drainage, micro-renewable power stations, and more public shared space for people to meet in. Suburbs could be the great untapped resource of a sustainable urban future.

_{*That’s a back-of–the-envelope calculation by the way. Some estimate a 2050 UK population of 70 million, up from 60 million today (http://news.bbc.co.uk/1/hi/uk/7055285.stm). Around 50 million (84%) Brits live in suburbs. Assuming an average population density of 20 people per hectare, that means 2,520,000 hectares of suburbia. We would be able to house all extra 10 million people by increasing the average density to 24/ha. If the average density of suburbs is lower than 20/ha that means that suburbia must be more extensive than 2,520,000 ha and there is even more space in suburbs to put the extra people.}