Overbuild

Overbuild is a relatively recent term that has come to mean achieving better land use by building over existing public assets to create new residential accommodation without the need to find greenfield sites. Thus, new apartments could be created above a library, university building or other building type.

More recently, an off-shoot of general overbuild is ‘rail overbuild’ – decking over railway lines and/or railway land to create new residential accommodation. Given the shortfall in UK housing, especially in London, the technique received significant national and international attention during 2018, primarily due to a study entitled ‘Out of Thin Air’ by global engineering consultancy WSP.

According to the report, rail overbuild represents a significant way to address London’s housing shortage and create 250,000 new homes without needing new land. Once land associated with railway infrastructure (station, rail tracks, yards) has been identified as developable, the ensuing build process is similar to any other.

WSP’s approach to overbuild and the basis for the 250,000 potential new homes it identified, was developed by Bill Price. It may build over a station, rail tracks and/or adjacent land and involves 12-storey developments that could comprise wholly residential or a mix of residential and commercial. The engineering required to build such developments in the railway environment is not significantly different to standard construction and engineering techniques.

[edit] Rail overbuild may offer the following benefits:

• A more efficient use of land – no new land is needed.
• May afford a relatively easy, cost-effective way to build new housing.
• A means to inner city regeneration.
• Makes use of existing construction technology.
• Can conceal rail tracks and goods yards.
• May allow more people to live in the city, particularly essential workers who often have to live far from the centre.
• Such developments may have very favourable public transport accessibility so residents may forego car ownership (so fewer cars on the streets, less parking required, lower congestion and emissions).
• Contributes to the ‘healthier streets’ initiative of the Mayor of London.
• Can provide pleasant environments, supporting new homes and jobs.
• Achieves densification that some UK local authorities will rely on for promoting growth and jobs.
• May be attractive to rail asset owners as a means of increasing non-rail fare revenue by attracting residential, commercial, retail and leisure uses.
• Local authority may receive higher community taxes, business rates, land value capture etc.

According to WSP, rail overbuild is not just about creating new homes, but also about creating new, safe, vibrant communities that provide greater transport mobility, reduce car ownership and contribute to the reduction of greenhouse gas emissions.

Following the publication of the original report, WSP published a follow-up entitled: 'Out of Thin Air - One Year On' which revealed a 14% increase in land availability. This increased the firm’s potential homes estimate to 282,681 new homes.

Download Out of Thin Air PDF

Download Out of Thin Air - One Year On PDF

[edit] Related articles on Designing Buildings

• Additionality.
• Air rights buildings.
• Airspace.
• Built to suit.
• Case study.
• Client requirements.
• Community infrastructure levy.
• Cost-benefit analysis in construction.
• Desk study.
• Developer.
• Existing use value.
• Future proofing.
• Hope value.
• Investment.
• Investment property.
• Legal agreements.
• National Planning Policy Framework.
• Residual valuation.
• Site selection and acquisition.
• Site appraisal.
• Site surveys.
• Speculative construction.
• Technical due diligence.
• Vendor survey.
• Yield.