Airspace Development in London

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Written by Taylan Tahir

Why should we develop rooftops?

In 2018, the Mayor of London and the Strategic Housing Market Assessment has identified that as a minimum we need to construct an additional 66,000 homes a year to keep up with the demand for housing. There were 39,970 Energy Performance Certificates (EPCs) registered in London in the year to September 2018-2019. These are a requirement for all new homes and as such are a proxy for the number of new homes built. Despite a 2% increase from the previous year the data identifies there is a circa 26,000 shortfall in the delivery of homes we need in London.

The ongoing battle to meet future housing supply is one that we seem to be losing.

As the London property market dips and dives, SME developers need to work harder than ever and keep pushing new opportunities to unlock sites. We see great opportunity in exploiting the development potential of the underutilised airspace above existing buildings.

This approach is supported by both; the revised 2019 NPPF (National Planning Policy Framework), which pushes for Local Authority policy to “support opportunities to use the airspace above existing residential and commercial premises for new homes” and the Mayor of London. The Mayor’s Draft New London Plan also recognises that London boroughs should be identifying sites suitable for “delivering residential above existing commercial, social infrastructure and transport infrastructure uses” (Policy SD8 Town Centres).

While this is by no means a free pass at planning stage for airspace development, it is a deliberate strategy put forward by Government that cannot be ignored by Local Authorities.

ExistingRooftop extension

Stack House, 2019. Bromley, South London. By MATA Architects

Residential Rooftop Regeneration

While the basic requirements for residential airspace development are similar to any type of development (ownership, planning consent, CIL and funding, installation of services, rights of light, party walls etc) there are also some specific challenges that need to be considered which include:

  • Potential design/technical constraints – including weight and loading of any additional storeys interfacing with an existing building; access from the ground floor; fire and acoustic requirements.
  • Construction logistics – Building at height above an existing (potentially occupied) structure.
  • Increased services provision/capacity.
  • Legalities – occupier/tenant rights; freeholder air rights.

There are also opportunities borne out of these challenges:

Modern, off-site construction techniques allow modular lightweight structures to be pre-assembled, delivered to site and craned quickly into place. This process minimises disruption during construction, mitigates health and safety risks and ultimately condenses the overall construction programme (and cost through reduced main contractor prelims).

Note: Professional advice should be sought at beginning of RIBA Stage 2 Concept Design or as early as possible from an architect or specialist to ensure concept designs (and subsequent planning consents) are suitable for this type of modular construction.

Pushback from leaseholders and residents due to disruption is a likely hurdle with any airspace development but can be overcome with a considered message outlining the overall benefits.

After construction, leaseholders can expect financial gains through a reduction in ongoing maintenance costs of the existing roof (the replacement of which will come with a 20-year guarantee), as well as communal areas if these are renovated.

Adding additional storeys to an existing building can provide more holistic opportunities to upgrade the fabric of the host building. More insulation could be added to the envelope or a new cladding system can envelope the entire building to create a total transformation and reposition an underperforming building. This again will decrease running costs and increase the overall capital value of the existing properties.

Stack House

We explored this approach at Stack House. We were commissioned by a developer (in this case the freeholder) to add a two-storey rooftop extension to an existing two-storey residential building to create an additional 4 flats in Anerley, South London.

The building is of very little architectural merit, tucked down a private vehicular side access away from views of the road. Our design proposes a complete transformation of the existing building including the overcladding of the ground and first floors to unify the scheme and re-position the building.

Added Value:

We took this brief a step further with our ‘stacked’ concept. The stepping out at each floor level helps achieve the following:

  • By stepping out at each floor we added 15% to the buildings’ footprint at 2nd floor and 20% at 3rd floor.
  • We added insulation to the existing ground and first floors, thereby increasing the buildings’ energy efficiency beyond the minimum building reg requirements.

Is my building suitable for an airspace development?

In order to make this assessment it is essential to consult a structural engineer as early as possible in the process. The first steps would include a comprehensive analysis and specialist testing of the existing superstructure (lateral stability and strength), foundation capacity and existing ground conditions. This assessment will also take into consideration access requirements for construction/logistics, fire protection and acoustics, and the provision of new services. It is also worth thinking about the most suitable construction methods from the outset as this will naturally influence the evolving form/design.

Ultimately, the determined loading capacity of the existing building will govern the scale of development. Buildings are not often constructed with additional loading in mind and as such may require specialist lightweight construction methods, additional reinforcement in places and new loadings to be distributed across the existing structure. A robust engineering solution in conjunction with a developed design will be paramount to the success of this type of development.

Alternative Airspace

The principal of delivering new housing on existing residential rooftops also extends to commercial, light industrial premises and even public infrastructure.

More supermarkets over the last few years have been capitalising on the demand for the ‘air rights’ above their premises, selling these for large profits to pave the way for development (and a captive audience of new convenience customers).

Publicly owned assets such as healthcare, educational and community buildings also have the capacity for well-considered airspace development. If implemented directly by Local Authorities, the profits and value generated from sales could be diverted to pay for upgrades to the host building, improving the amenity of new and existing residents.

The Future of Airspace

Large landowners such as TFL continue to capitalise on the vast amounts of airspace above train and tube stations. The modest train station typology of the past has now become the monumental vertical city of the present, where people live, work, shop, socialise and… also get the train.

Hamburger Deckel project in Hamburg, Germany

Ambitious infrastructure projects such as the Hamburger Deckel in Hamburg, Germany take a big picture approach to airspace development. One of the largest highways in the country is covered with green space and new buildings tackling some of the larger social issues associated with the proximity of traffic and people as well as adding new value and amenity to existing communities.

As our communities grow and work and leisure become more integrated so will our future living environments. We could see retail spaces appearing above bridges spanning rivers; new houses for sale suspended over a reservoir or a block of flats spanning roads and motorways. Everyone will want to live above their favourite museum or art gallery.

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