Making parts of London more dense

How do we build more homes in London? The Mayor’s latest exercise assessing needs suggests we need up to 690,000 over the next ten years, but a parallel exercise looking for land only came up with sites for 420,000 homes.

The usual debate is whether or not we build in London’s greenbelt to make up the difference. But there are at least three good reasons not to go down this route to solve our problems: there are an awful lot of protected habitats that we really cannot build on; building sustainable developments around transport hubs and avoiding those habitats could only deliver (in Andrew Lainton’s estimation) 72,000 homes; and if we ignore these,  it could lead to more low density, car-dependent urban sprawl, which the greenbelt was established to prevent.

The alternative, or perhaps complementary, approach is to make London more dense, particularly around transport hubs in sprawling, low density outer London. This has actually been pushed for over a decade by Ken Livingstone and Boris Johnson with the London Plan, the main planning document for the capital.

There is a lot more to be said about that debate, but it isn’t my purpose with this blog. Instead, I have indulged in one of my hobbies and done a rough-and-ready analysis of the current density across London, by local electoral ward.

My methodology was as follows. I started with the ward boundaries, and the ONS household estimates from 2011. I then chopped out all the areas covered by the land uses which I reasoned we cannot build on.

• greenbelt
• metropolitan open land (strongly protected in planning policy)
• parks, commons, allotments, nature reserves and other important green spaces
• railway lines with a 5m buffer either side

The data for these came from the London Datastore and extracts from OpenStreetMap.

I considered cutting out areas covered by roads, but then found it would take so long for my software package QGIS to process the data that I’d lose interest! So, given that roads cover pretty much every area, I decided it wouldn’t make a significant difference and left them out.

I also didn’t cut out industrial or commercial areas, for three reasons: first, often commercial buildings have flats above; second, the coverage in OpenStreetMap is too inconsistent; and third, while many should be retained for this use, there are also lots of areas that could be redeveloped for homes, or as mixed-use sites.

So given these caveats, I calculated the number dwellings per hectare of land that could potentially be built on. Here’s the result:

The green area is all the land that can’t be built on. The rest is coloured from deep red for very high density to light pinky grey for the lowest. I haven’t put a legend on because, well, it’s a very rough approximation. You can see obvious problems with the data, e.g. where Heathrow airport sits, and the Thames Gateway with lots of strategically important industrial land as well as lots of sites for new housing.

So what could densification achieve? Well, let’s say we increase the least dense half of London and brought it all up to the median density. That would increase the number of homes by 815,000!

I haven’t gone any further with these because it is such a rough calculation. If I can get my hands on better data to account for the flaws mentioned, I’ll give it another whirl. But it would be quite interesting to take an area I know really well and look for development sites, and see whether they could be brought up to that median.

Update see part two where I look at density and public transport accessibility.