Upward Extensions have the potential to provide a quicker and more cost-effective way of creating new affordable homes – and could be key to meeting current housing demands. Here, David Gatehouse at Langley Structures Ltd explains more about extending upwards and its feasibility.
In 2017, the Government set private housebuilders, housing associations and councils a target of building 300,000 new homes per year by 2025 to meet the demand for housing in the UK. As part of that pledge, it is important that the right type of new housing is delivered, including affordable homes and those for social rent in the areas where they are most needed. The on-going shortage of suitable housing means the number of people in temporary accommodation remains a serious issue for local authorities. Ministry of Housing, Communities and Local Government (MHCLG) statistics show that at the end of March 2020 there were 93,000 households living in temporary accommodation in England, an increase of 9.4% compared with the previous year. The figures also show that 65% of these are in London alone. The cost of temporary accommodation to local authorities is also substantial with councils across England spending £997 million on temporary accommodation in 2017-18.
One of the key challenges for meeting housing demand is the availability of land, especially with the need to protect valuable green areas in and around towns and cities. In 2017/18 549,342 m2 of green land was built on to ease the demand for housing, however this solution is not sustainable in the long term and therefore new approaches are a necessity. For example, London needs 66,000 new homes a year, yet more than one-fifth (22%) of the land within the capital is designated Green Belt.
One possible solution is extending upwards and utilising the airspace above existing buildings to create new dwellings. Estimates of the number of homes that could be created in this way in UK towns and cities vary. However, a study conducted by Knight Frank suggests that in London Zones 1 and 2 alone, as many as 40,000 new homes could be built on top of existing buildings. Although not all of these sites will be suitable, it does demonstrate the potential that exists at the rooftop level.
The concept of upward extension has repeatedly received support from the Government. Since July 2018 the National Planning Policy Framework (NPPF) has stated that planning decisions should support the use of the ‘airspace’ above buildings especially if “the development would be consistent with the prevailing height and form of neighbouring properties and the overall street scene”.
Furthermore, the Government’s recent revision of the Permitted Development rules makes it easier to utilise rooftops. The updated rules allow the construction of up to two additional storeys on purpose-built, detached blocks of flats, subject to certain conditions. This includes that the existing block must be three storeys or more and the extended building must not be more than 30 metres high.
This approach to the creation of new homes is particularly suited to social housing providers as they already own the building and extending upwards allows them to make the most of an existing asset. In addition to solving the challenges of land acquisition, extending upwards can also offer a more cost-effective approach to housing delivery compared to new-build or in-fill development. With no need for ground- or infrastructure enabling-works, new homes can be created at a much lower cost per unit. These cost benefits may be particularly important for local authorities and housing associations for whom optimising the use of limited capital is essential.
Another key advantage of upward extension is the speed of delivery, especially when the selected solution makes use of modern methods of construction (MMC). For example, there are systems available that consist of a lightweight, robust steel frame, which can be built into modular cassettes off-site. These can then be delivered to site as required, lifted to the roof and positioned. The insulation and external cladding can then be installed, and the new flats connected to the building’s services.
This approach also means minimal disruption for residents as typically they can remain in their homes throughout the build. Engaging with tenants to explain the intended work and formulate a plan that will benefit them is of course essential and demonstrating that disruption will be minimised can be key in alleviating their concerns. This also has a benefit for housing providers as it eliminates the need to find suitable alternative accommodation for the residents during the build.
A further benefit of extending existing purpose-built residential buildings is that local amenities and transport links are already present. It is also important that the design and construction of the extension provides high quality homes that are safe and comfortable for residents.
Finally, these developments also provide the opportunity to integrate renewable energy technology and other features to help reduce household energy consumption and improve the sustainability of the building. For example, photovoltaic panels and ground source heat pumps can be added to lower energy costs as well as sun tubes that can introduce more natural light. Green, biodiverse and blue roofs are also an option to increase biodiversity and improve rainwater management. When the upward extension is carried out as part of a wider refurbishment, energy efficiency upgrades can be applied to the whole building to deliver benefits for all residents.
The scale of projected demand for new homes in the coming years means the green-field first strategy that has dominated housing delivery in previous decades is no longer viable. Local councils and social housing providers are ideally placed to lead on the implementation of new approaches to delivering the high-quality homes that our towns and cities need. Extending upwards and utilising innovative offsite and modular solutions offer a cost-effective way of creating these homes and the wide-spread adoption will help address the issues we face.