It is taking some time for those interested in tackling the shortage of housing to ‘get’ the potential of ‘custom-splitting’. This is simply a way of coordinating and increasing the scale of subdividing existing houses to harness the appetite for custom- or self-building to enable those who would want to downsize-in-place to do so. There has never been more space in residential use per head of population and cusping is a way of sharing it out. Until ways to redistribute the housing have been properly explored, the need for 300,000 new-built homes with many in green belts and other peripheral locations cannot be fully assessed or known.

‘Custom-splitting’

The National Custom and Self Build Association estimates that up to half of all households are interested in self-/custom-building. The Government would like to see the number of self-/custom-built homes being completed each year is unlikely to reach 20%. With the official target increased to of the 300,000 homes this would amount to an increase from about 12,000 to 60,000, a fivefold increase that will not happen without more Government assistance.

The potential of cusping was examined in 2016 by the Intergenerational Foundation, which estimated that there could be as many as 4.4 million dwellings readily available for sub-division. In 2016 the All-Party Parliamentary Group on Housing and Care for Older People received evidence that there could be 8 million households looking to downsize if attractive smaller dwellings were made available. This emphasises the need to increase the supply of housing suitable for the elderly. A silver bullet is one that could hit more than one target, while cusping is a green bullet that could hit up to 15.

The benefits of cusping

Most if not all of the following benefits could or should count as material planning considerations in both plan-making and decision-taking:

• Reducing unsustainable levels of under-occupation in urban, suburban and rural areas
• By making energy upgrades a condition of the grant of planning permissions or Local Development Orders (LDOs), cusping could help upgrade the existing housing stock, of which 60-70% is currently at the equivalent of EPC (energy performance certificate) rating D or below, to EPC B and above and help meet the required rate of about 750,000 such upgrades a year until 2040. This would also reduce the possibility of either household falling into fuel poverty.
• Cusping would enable older households to ‘downsize-in-place’ in what could evolve into ‘lifetime neighbourhoods’. This could also involve adaptations of all or part of properties to Lifetime Home mobility standards.
• Through the choice of partners and the design of the accommodation, the process of cusping could involve the respective households seeking to meet their current and foreseeable needs in terms of caring for children, the sick, disabled or elderly (obviously on the understanding that personal circumstances are subject to change).
• The choice of partners would involve matching financial needs and also the other resources and skills that could be shared and contribute to the efficient and cost-effective implementation of a subdivision.
• However proficient the parties involved, many projects are likely to create some work for smaller tradesmen and builders.
• The parties could negotiate and choose how any garden areas could be subdivided in the short and longer term (without building on them), allowing ageing households to maintain a larger garden than is normally available with smaller properties and those designed for the elderly. This aspect of downsizing-in-place can also help to overcome the under-estimated problem/excuse of clearing the loft, as stuff can just be moved to the part of the roofspace being retained.
• Both parties would be able to negotiate and choose between renting, buying or renting-to-buy all or part of the respective parts, possibly with some elements being shared (for example access arrangements, garden areas, garages, or sheds).
• The original owners could release equity without re-mortgaging – renting out the separated dwelling could provide an income, possibly through rent-to-buy. This might make custom-building (through splitting) accessible to the younger generations that are currently being excluded due to the high upfront costs.
• The density of people (and so the potential customer base for local services and facilities) would be increased without building on open land (some brownfield land has become very biodiverse), including gardens. Cusping would also take advantage of existing infrastructure such as roads and drains.
• The issues surrounding the non-implementation of planning permissions being experienced in the new-build sector would be avoided as custom-building of all types effectively conflates supply and demand.
• The works involved in sub-dividing properties represent a very efficient use of materials and labour that are both increasingly scarce and expensive, even inside the EU. It would be much cheaper to complete a conversion to self-contained dwellings than to start on a bare site, even though the works would not be zero rated but VAT was charged at 5%
• By matching those with space to spare that they are willing (and keen) to share with those on the self-custom-build registers, local planning authorities would have a reasonable chance of meeting their legal duty to provide serviced plots.
• Cusping at scale would provide a realistic ‘alternative’ to conventional means of supplying housing that should be fully explored before permitting new greenfield building (including Green Belt release). Subdivisions in existing residential areas would help to reduce the pressure to develop peripheral estates in the open countryside.
• Subdivisions providing self-contained accommodation would be consistent with the proposal to change the General Permitted Development Order to allow upward extensions without express permission, so long as a separate/additional dwelling would be created.

All these matter are non-trivial and regularly missed by other proposals to address the housing crisis. Cusping would also represent a more ‘sustainable’ form of development’ than all forms of residential new build.

Helping it happen

The central government grants available for custom-building should be made available for cusping. Local planning authorities persuaded of the benefits of cusping should be prepared to make grants available to cover the upfront costs associated with design and/or conversion – these could be recovered either on completion of the works or as a legal charge on the property that would be repaid on its later sale. Policies in local plans should set out the circumstances when cusping would be supported (or opposed). This could be greatly simplified through the making of LDOs (for example to specify energy standards and minimum room sizes).

Registers should be kept of property owners wanting to be introduced to those on the custom-building registers, who should also be asked to include their willingness to engage in the subdivision of an existing property rather than wait for up to three years in the hope of being lucky enough to receive an offer of a serviced plot at an acceptable location and price.

A web site is being developed to match home owners with potential cuspers.

Challenges

Once the planning system has paved the way, the main challenges might be for designers to find efficient ways to meet the access and space requirements of the original and prospective households, to specify energy efficiency and noise insulation measures, and to separate the services (i.e. plumbing, drainage and electrics). Divisions might be horizontal (i.e. into flats) or vertical (i.e. into semis). Small extensions might be required for additional hallways, stairs/lifts, bathrooms or kitchens (also to be covered in the LDO). There might also be challenges for lawyers and lenders to tailor legal documents and financial arrangements to the needs of the parties.

Objections

There might be objections from those afraid of increased demand for on- street parking. This concern should not be allowed to get in the way of a process that would meet so many interests of acknowledged importance; but it would be possible through the use of conditions (or the terms of an LDO) to address this potential impact, and even to use cusping to encourage the transition to a lower level of car ownership delivered through sharing ultra-low-emission vehicles (with autonomous vehicles coming into view).

Cusping is a huge opportunity for designers and surveyors in designing and specifying the means of sub-division and for the manufacturers of the thermal and acoustic panels that will be fundamental to the success of these projects.

Daniel Scharf MRTPI blogs at www.dantheplan.blogspot.com