In setting out to do our research, we were particularly aware of typical planning, design and technical constraints that impact on the potential for sites to be suited to extension, including:
• the structural capacity of the building to support additional loading;
• the feasibility of extending existing lift cores or adding a new external lift cores;
• the presence of restrictive telecommunications equipment and other services at rooftop level;
• the local character, and
• planning considerations such as Conservation Areas, local and London-wide sensitive views ;
• good access levels to public transport; and,
• the need for car parking provision. Using satellite imagery, we identified 475 rooftop sites across Camden suitable for development.
These sites excluded any building stock that was subject to planned or future regeneration. These sites amounted to 198,660 sqm of developable rooftop space. Taking an average of 60sqm per home, and utilising 75 per cent of the suitable floorspace, we calculated that rooftops in Camden have potential to deliver 2,485 new homes. This amounts to 28 per cent of the London Plan 2015 housing target for Camden. We identified a number of building typologies that might be suitable for rooftop developments, subject to these constraints; design solutions for these are illustrated as part of this article. From our findings in Camden we extrapolated the typical development density of 1.14 home per hectare to the whole of London, which delivers 14,330,080 sqm of rooftop space. Using an average of 60 sqm per home, this amounts to 179,126 new homes or 42 per cent of the London Plan 2015 target for housing.
The study acknowledges that this extrapolated figure is approximate, but as the case study borough was fairly constrained, we believe it could be a fair reflection of the potential for rooftop development across London. The research has also been presented to the GLA, who received it positively and who indicated they would welcome further London-wide research to inform evidence to underpin new policies and guidance related to rooftop development. Rooftop development offers a wide range of benefits which can include: increasing opportunities for small and medium sized developers and construction companies, providing a potential new funding stream to assist affordable housing delivery if done at scale, and using offsite manufacture to speed up the delivery process, amongst a range of benefits for existing residents and leaseholders living in suitable buildings. There is significant potential within London’s built fabric for intensification. Small sites have traditionally not been the focus in terms of their contribution to new housing supply, particularly as often these sites can be the most difficult to guide through the planning process.
We need adequate policy support for this type of development in London, with recognition that with careful design measures, this could be an altogether sustainable way to grow London, keeping existing communities in place and resulting in local and wider economic benefits.