The application proposed single-storey front, side and rear extensions to 4 Sultan Street, Beckenham BR3 4QS. The site is located on the west side of Sultan Street at a corner with Churchfields Road. The host dwelling is an end-of-terrace unit with a paved front drive and rear garden. The end-of-terrace position made the proposed front extension particularly significant, as it would affect the outlook and daylighting of the adjacent property at the end of the terrace row.
The most technically precise element of our objection concerned the BRE guidance on tunnel effect. BRE Site Layout Planning for Daylight and Sunlight (paragraph 2.2.18) specifically addresses circumstances where an extension already exists on one side of a window and a new extension is proposed on the other. In this case, the adjacent property had a repurposed room used as a home office since the COVID-19 pandemic. Since the room had been habitually used as a working space, it qualified for consideration under habitable room standards.
A garage already existed on the opposite side of the window in question. The proposed front extension to No. 4 would create a tunnel effect — two obstructing elements on either side of the adjacent window, severely restricting the cone of sky visible from that window and causing a material loss of morning light to the home office. This was a textbook application of the BRE tunnel effect guidance, and the failure of the applicant's design to acknowledge it was a significant weakness in the submission.
Policy 6 of the Bromley Local Plan requires extensions to respect or complement the scale, form and materials of the host dwelling and to maintain gaps between buildings where these contribute to the character of the area. The front extension proposed was excessive and out of character with the existing terrace, disrupting the consistent rhythm created by the garages and front elevations of the properties in Sultan Street. Policy 37 requires all development, including extensions, to achieve a high standard of design — a requirement the proposed front extension failed to meet.
The rear extension, while not the primary concern, compounded the issues raised by the front proposal. The north-facing aspect of the rear garden of the adjacent property meant that any rear extension to No. 4 would have a disproportionate impact on available light to that garden and the rear living spaces — adding to an already harmful cumulative effect when considered alongside the front extension proposals.
The London Borough of Bromley refused the application. The tunnel effect argument — grounded in specific BRE guidance — was central to the refusal, alongside the harm to the character of the terrace and the streetscene impact of the front extension. The technical precision of the objection, referencing the exact paragraph of BRE guidance, provided the council with a clear and defensible basis for refusal.
The BRE tunnel effect guidance is a powerful tool in objections to extensions that flank windows already affected by an existing obstruction. Many extension applications do not acknowledge this guidance, creating a vulnerability that a well-prepared objection can exploit. This case also shows that rooms used regularly as home offices since the pandemic can qualify for habitable room daylighting standards — a point increasingly relevant as remote working has become normalised.
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