The London Plan contains an important new policy on small site intensification (25 units or less) designed to help bridge the gap between housing need and the SHLAA assessed numbers.
It will help though not fill the gap, however the risk is that if not designed well it will be used as a presumption in favour free for all for poorly conceived schemes.
We have learned a lot internationally of best practice in zoning for intensification. the best defence for outer boroughs that fear this is to plan it and design it with design codes, as the London plan draft rather weakly hints at.
As a case study as to what this might look like ill take Greenford it that it is high;y accessible but has lower densities that some nearby areas such as Alperton, Southall and Ealing and has few ‘nicely designed’ suburban estates. It also has industrial areas which are prime candidates for intensification with mixed uses being narrow and next to canals and open spaces rather than large industrial areas such as Park Royal which has many areas best kept free of residential on noise and HGV amenity grounds.
The scope of this article however is on residential intensification. Ill look here at the area just south of Grenford tube station, all 30s Osbert Lancaster bypass variegated style housing.
The key for zoning is such areas is to classify by back lot line and plot depth. The back lot line is the line at the rear of the plot. There are many plots where houses back onto houses which limits the density because of privacy concerns. There are also as you see lots that back onto open spaces, rear lanes, railway lines and industry which have much more potential, as do corner lots.
The other main parameter is number of lots in a scheme. A key concept here is ‘graduated density zoning’ where the number of allowed units is increased as the number of lots is increased, as lesser set in requirements mean more units can be accommodated on site.
In this suggested approach you would classify lots according to these parameters and then do test fits of different development forms on these lots. You would then set down a design code, potentially allowing permission in principle for compliant schemes, zoning in good practice and zoning out undesirable forms (such as controversial end on schemes).
To take an example a single semi plot with a depth of less than 40m might only allow for redevelopment to three storys and maximum 3 units. Combine two lots and you could go up to 4 storys and 4 units. For deeper lots without a residential rear lot line this could be increased to six storys and up to 10 units, 20 units for 4 or more combined lots, 25 for 5 combined lots. Corner lots could gain an extra story and a 20% unit boost. FAR would be used to prevent the system being gamed with overlarge unit sizes, indeed with FAR you need to rely much less on complex dwelling mix rules.
Such schemes are controversial everywhere, but they need to be introduced if we are to be serious on intensification. the GLA should sponsor with Boroughs a number of pilots, without the cop out of stripping all street names out of the final report.