According to a discussion paper and questionnaire (26-page / 1.5 MB PDF) published last week, the Council has become concerned about the potential consequences of a trend for subterranean development under residential gardens and existing basements in the borough, and intends to produce a supplementary planning document (SPD) next year setting out requirements for basement developments.
The Council said the number of planning applications involving basement developments had increased by nearly 50% between 2013 and 2014 and the sizes and depths of proposed excavations had also increased. It said the resulting 'super-basements' were energy intensive, requiring artificial lighting, ventilation and sometimes groundwater pumping. It said the impacts of excavations on local drainage patterns, ground movement and rooting space were complex but could include increased flood risk and threats to neighbouring trees and buildings.
The document sought views on proposals to introduce an SPD with guidance and requirements relating to: the amount of undeveloped or garden area that must not be built on; the general depth, drainage and volume of subterranean developments; impacts to existing trees and shrubs; sustainable design specifications for basements; and the mitigation of both site specific and wider cumulative impacts of development.
The Council also requested feedback on proposals to seek detailed supporting documentation and technical evidence in support of basement planning applications.
"We're seeing a growing trend towards big basement excavations as the value of homes in Islington – particularly large ones – continues to soar," said councillor James Murray, the Council's executive member for housing and development in a statement. "We need firmer rules to protect the borough's gardens and trees for the future, and to prevent long-term impacts on the character and structure of homes further down the line."
The consultation is open until 27 January.
The Council said it intends to develop a draft SPD for further consultation in spring 2015.