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Rooftop extensions are well and good – but design quality is paramount

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London’s rooftops have a vast potential to deliver more housing, but the proposed new permitted development rights could prove disastrous, write Riëtte Oosthuizen and Simon Owen of HTA Design

In tandem with the Autumn Budget, the government launched a consultation on planning reforms to increase housing delivery and address the poor state of high streets. The intention is to ‘make the most effective use of existing buildings both for business and residential use’. The benefits are evident: it will lessen pressure to build on the green belt and back gardens and, hopefully, offer a lifeline to failing town centres. 

New permitted development rights are proposed to allow existing premises in ‘typical high street uses’ to change to a wider range of uses, such as leisure and community uses, offices or homes. 

Subject to prior approval, new permitted development rights are proposed to allow additional storeys above certain buildings in commercial and residential use. The emphasis is on delivering new self-contained homes, not simply additional habitable rooms. The government is inviting views on how this development right might be used in practice and how local design codes could help to encourage the take-up of the proposed rights, while improving design quality. 

There can be no excuse to create a system where an extension to a building will provide substandard homes

Encouraging a greater variety of uses within high streets is certainly a positive move, although prohibitive rents charged by certain landlords might prohibit some premises for community or leisure uses if this ‘permitted development right’ is not also supported by site allocations or local plan policies. It is slightly disappointing that there is an ‘or’ included in the range of temporary use class changes that would be allowed. Many of London’s lively high street uses have premises where there is a variety of uses within one space.

HTA Design has long advocated the vast potential of London’s rooftops to deliver additional housing: in a study undertaken for Apex Airspace in 2016, the capacity of residential rooftop development across London was calculated to be about 180,000 new homes. The principle of rooftop development is widely regarded as a logical step in boosting housing supply. 

There is a question around whether permitted development rights to achieve additional housing supply will lead to good-quality homes. As such, it is positive that a focus on design quality is contained within the consultation. It is expected that the Raynsford Review of Planning will largely condemn the poor quality of some homes created as a result of the permitted development rights of offices to residential: national space standards are not adhered to, outdoor space is not provided and there is no requirement to provide affordable housing, for which there is desperate need. 

There is a definite need for careful consideration of design implications relating to permitted development rights for upwards extension. Implications for roof and streetscape could be disastrous if there is a free-for-all. It is also important that there should be some consideration of existing residents’ amenity and, possibly, compensation for disruption. 

The consultation document acknowledges there are issues that will need to be considered: siting, appearance of the upward extension, its impact on the amenity and character of the area and impact on neighbouring premises. These elements suggest that a new permitted development right will still be complex.

As planning consultants and architects, we find that small-scale schemes in suburban areas attract more objections than many larger schemes. This means that upward extensions in existing residential areas where there aren’t already taller buildings adjacent will probably be quite unpopular. The prior approval process would need to ensure that an extra floor or more on an existing building would be subject to detailed assessments. 

Impacts normally assessed by planning applications would still need to be considered in the prior approval process – issues such as overlooking, overshadowing and daylight or sunlight impacts. 

Whether a proposed upwards extension fits in architecturally with an existing building and the local context would need to be judged as part of the prior approval process – property owners wouldn’t normally want to blight their building with a devaluing ugly extension. Design codes could assist but would require local authorities to be prepared and commit resources. There can be no excuse to create a system where an extension to a building will provide substandard homes – from the inside or the outside. 

This column was written by Riëtte Oosthuizen and Simon Owen of HTA Design and supplied by the Association of Consultant Architects (ACA), the national professional body representing architects in private practice in the UK. Membership for eligible practices is free. For further details go to www.acarchitects.co.uk

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