Camden councillors have been claiming that they expect the redevelopment of 156 West End Lane to deliver 50% affordable housing, but figures from their own 2014 report into primary school provision predict only 25%.

[UPDATE 5.30pm: Cllr Phil Jones has left a comment below explaining that this 25% number is outdated, and the sale to the developers was made on basis of 50% affordable housing]

There is heightened interest in this because the Liddell Road redevelopment proposals have no affordable housing component. Camden is arguing that Liddell Road and 156 West End Lane need to be considered together (which is difficult when one is at planning stage, and the other is nowhere near).

The data used for Camden’s recent work into determining future primary school provision shows assumptions about the housing mix at both 156 and the (much further off) O2 car park redevelopment. In neither case is 50% affordable housing on the cards.

The data given is based on number of units, while the quota for affordable housing in a development is based on floorspace. Nevertheless, it’s quite possible to do some back-of-the-envelope calculations to make a good guess at the floorspace figure. All the data can be found in Camden’s Primary School Places Planning Report 2014.

At 156 West End Lane, Camden is assuming a total of 93 units will be built of which 65 would be market and 28 would be affordable (there’s actually an error in their arithmetic in the table, so this could be 27). Assuming it’s 28 units, then that’s 30% of total units. But what about floorspace?

To get an idea of floorspace, we can use the size of flats at the West Hampstead Square development. They vary slightly but roughly speaking 1-beds are 52 square metres, 2-beds are 80 sqm, and 3-beds 94 sqm. There are no four or five bed properties listed at the moment at West Hampstead Square, but there’s a 4-bed flat on the market locally that’s 110 sqm. Modern five-beds are rare and older properties tend to be larger, so lets guess on the low side (which would help Camden’s formula work) and say 140 sqm.

This would give us market unit floorspace of 5,294 sqm

If we assume (again to give Camden the benefit of the doubt) that the error in the table is due to an affordable housing 4-bed flat not being recorded then affordable floor space would come to 1,814 sqm.

Total floorspace: 7,108 sqm of which 25.5% is affordable.

Clearly there are a lot of assumptions here – but unless there’s an enormous discrepancy in the size of affordable and market properties with the same number of bedrooms, it’s impossible to see a situation where we get close to 50% affordable housing.