Birmingham is getting bigger, and is going to continue to get bigger still. This is good news. It is getting bigger because it is a successful and popular city where people want to live. Apart from a period in the late 20th century when the population went down, due to damaging deindustrialisation and the loss of tens of thousands of manufacturing jobs, Birmingham has been growing bigger ever since it started.

The emerging Birmingham Development Plan (BDP), the City Council’s blueprint for the future growth and development of the city, reckons that the growing population will require an additional 80,000 dwellings by 2031. It calculates that 45,000 of these can be built within the existing urban area on previously-developed land (brownfield) and by “densifying” existing settlements.

But 6,000 dwellings are proposed to be built on agricultural land in the Green Belt, on the eastern edge of Sutton Coldfield. The BDP grandly calls it the Langley Sustainable Urban Extension (SUE) – can’t we just agree that every new development now has to be sustainable by law, and not have to keep repeating the term?

The orthodoxy of sustainability specifies that building houses on brownfield land should take priority over building on agricultural land.

This can make more efficient use of existing infrastructure like roads and bus services, and of existing services like schools, shops and health centres. There is a vocal lobby protesting that the Langley SUE is in fact unsustainable development, and calling for the proposal to be scrapped. A public inquiry later this year will decide.

By historical standards, this proposed urban extension of 655 acres (273 hectares) is minor. Compared to the 1911 expansion of the city boundary, for example, which took in 24,000 acres of undeveloped land in Quinton, Harborne and Edgbaston to build on, the Langley proposal is insignificant. I expect it to be approved, although with the unpredictable Eric Pickles still in charge of Local Government after the recent Cabinet clear-out, one can never be certain.

Part of the Langley scheme’s claim to sustainability is in its proposed residential density. Twentieth century urban expansions were typically wasteful of land by being built at low density. At low densities, places are far apart, discouraging walking and cycling, and public transport becomes inefficient, encouraging people to drive. Langley’s proposed average density is 40 dwellings per hectare – not a high density by any means, but respectable. We could call it compact.

If it is to be built, what kind of a place could it be? It presents an opportunity to make a very special place, a model of new development. For all Birmingham’s enormous growth in the 125 years since it became a city, the quality of what it has built has been mediocre. Newly-built suburbs like Kingstanding and Quinton were missed opportunities. Need I mention Castle Vale or Chelmsley Wood?

As a teenager in the 1960s, I used to cycle the country lanes around Langley. Since then, much of the land around those lanes has been built over by an unplanned and illegible sprawl of culs-de-sac spreading out from Walmley, just the kind of dreadful and placeless development of which we have unthinkingly built too much.

This development now creates a particular difficulty on the boundary of the Langley site: roads which were classified in the car-dominated planning culture of the time as distributor roads. The inflexible formulae of the time specified that houses could not face these roads, so they are lined with high brick boundary walls. These hostile edges will present a problem for those planning how to build on the opposite side of the road.

There are only two residential districts built in Birmingham in the last 125 years which we can describe as special and distinctive places – Bournville and Moor Pool in Harborne. Both of them are very popular places to live, but both are over 100 years old. Langley is an opportunity to make a 21st century version of this kind of place.

As well as 6,000 dwellings, it will have two primary schools, a secondary school, health centres, parks, shops and other facilities. It needs to be imagined not as a big housing estate, like so many earlier developments, but as a distinctive small town in its own right.

Langley will be built to a masterplan, which will establish a structure and principles of development that will coordinate the contributions of the number of developers who are likely to be building parts of the whole. Tenders have been received from experienced masterplanning consultants, and a shortlist was made last week.

Other towns and cities are experiencing the same kind of housing pressure, and urban extensions of this scale are currently receiving a lot of attention. One of the best so far is Upton, on the western edge of Northampton, and another is Newhall, currently being added to Harlow in Essex. Both were masterplanned by excellent urban designers (EDAW and Studio REAL respectively), and they are not suburban sprawl. They are attractive and unique urban places, like small market towns, on the edge of the countryside.

Building over countryside is contentious, but it is probably necessary, as well as building within the city, if we are to house the growing population. But if we are to build on the cornfields, aspirations and standards need to be high, to produce a place which will be wonderful to live in, and bring visitors to Birmingham from all over the world to see it, just as Bournville does.

These visitors currently go to see the best new European housing developments, places like the Western Harbour in Malmo, Hammarby Sjostad in Stockholm, and Vauban in Freiburg. These are in the league that Birmingham should aspire to join.

We need an excellent masterplanner appointed, developers with imagination who employ the best architects, and planning officers with the knowledge and clout to ensure that the highest standards are set and delivered. No small task, but we shouldn’t accept anything less.

* Joe Holyoak is a city-based architect and urban designer