Tighter rules on basement excavations introduced by the planning authority are clamping down on the "digdown" trend.
Developers at 44 Kenilworth Avenue, Wimbledon Park, are among the first to be hit by new rules, which only approve significant excavations if a drainage strategy is produced.
The controversial extension, which will make space for an ensuite bedroom, hall, storage and lightwells, was approved, subject to conditions, at a planning meeting on Thursday, March 27.
A petition against the development, which includes a basement excavation and rear dormer roof extension, was signed by 27 residents.
Neighbours raised concerns about the basement's impact on watercourses, causing an increased flood risk and negative impact on the stability of adjoining houses.
Concerns expressed in 18 objection letters to the committee also included noise and disruption caused by building works, impact on a tree outside the house, loss of privacy and light pollution.
However, the development is one of the first to be subject to Merton's first basement policy, set to be formally introduced at the next full Council meeting on June 4.
Applicants for significant basement extensions now have to pay experts to assess impacts on drainage, flooding, ground water conditions and structural stability before excavating.
The proposed basement in Kenilworth Avenue has been significantly reduced in size from the original application, now located under the front part of the house, instead of the whole house, with no games room.
Homeowners now also have to produce a working method statement detailing the management of loading and unloading materials, control of dust and protection of the street tree.
The move comes after Kensington & Chelsea council announced similar restrictions on basement extensions, following concerns about noise disruption and structural damage to homes as underground extensions rise in popularity.
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