The London Assembly has been told that onerous planning processes are preventing the capital from adding up to 320,000 new homes by expanding buildings upwards. Despite national policy changes encouraging upward extensions, including permitting mansards on suitable properties, uptake remains low, with only a few hundred applications per year for half a million eligible properties.
Planning barriers hinder housing potential
Nicholas Boys-Smith, Founder and Chairman of Create Streets, told the London Assembly Planning and Regeneration Committee that the lengthy planning process is putting residents off. "Under the current planning and regulatory regime, I think the potential practically, not spatially, not physically, of upward extension remains uncomfortably modest," he said. "We're getting 500 applications per year in London recently, it's far too low." He highlighted the financial risk: "The amount of work involved, the risk of not getting planning permission, you know, the fact you need to pay planning consultants, architects, you need to spend probably tens of thousands of pounds before you know you've got those extra bedrooms or that extra flat on top of a bigger building."
Immense spatial opportunity
Boys-Smith noted that "low-end estimates" for homes created through upward extensions are about 140,000, with an upper end of 320,000. "Critically, and I really want to stress this point, the number of bedrooms is from 300,000 to 680,000," he added. "The bedrooms really matter, even though I know it's not in national housing targets, because bedrooms reduce homelessness." He emphasised that spatial opportunity exists but requires planning policy change.
Permitted development rights not working
Boys-Smith explained that permitted development rights (PDRs) have not worked as intended. PDRs allow adding up to two storeys to detached houses or one storey to bungalows or terraced houses without full planning permission. However, a lack of "planning understanding" from local authority officials has kept uptake low. "There was a very, very visible and sharp distinction between uptake for PD that did and didn't require prior approval," he noted.
Local Development Orders as a solution
He recommended mass rollout of Local Development Orders (LDOs) and locally developed design codes, which apply to defined areas. A Create Streets report found densification in South Tottenham, Chelsea, and Tower Hamlets was achieved through clear design codes and local orders. "The real game here is not big changes on big blocks of buildings," he said. "The real, real opportunity here, if we as a polity and as a country wish to take it, is to allow streets organically to grow again in a way that is acceptable to the local population." He added that exponential increases in homes occur when councils "turbo-charge" through Supplementary Planning Documents (SPDs) or LDOs.
Experts call for clearer guidance
Dr Charles Gillot, Senior Sustainability Engineer at WSP UK & Ireland, said changes to the National Policy Planning Framework (NPPF) had "not been a fantastic success," with most upward extensions delivered on a larger scale rather than by individual homeowners. Experts also suggested the next London Plan, due for consultation soon, should include clearer city-wide guidance on upward extensions.
