The Little Black Box

Sebastian Mongillo, London, 2018


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Sebastian Mongillo     Download Original

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Single-storey rear extension with an external cooking area to a semi-detached mid-eighties brick house.

The Little Black Box is the extension of a semi-detached mid-eighties brick house within the unadopted Heathway Road in Blackheath, South East London.

The project was conceived as a simple monolithic black box volume with bespoke BBQ and a decking area.

The project provides an extension to the living space under the permitted development scheme. The exterior decking consists of a complete outdoor kitchen facility complete with fire oven, bespoke stainless steel BBQ and storage area.

Parametric design approach, fast build, sustainability, cost effective and the use of non-traditional construction methods were the inspiration behind the design of the project. All the materials were carefully chosen from reputable and sustainable sources. The construction method was inspired by toy blocks in which BIM was used to design a system like a big jigsaw.

Self-insulated panels and timber pieces pre-cut during the manufacturing process allowed for a simple and fast assembly, resulting in an eight-week programme. The use of SIPs (Structurally Insulated Panels) were specifically chosen for high-energy efficiency, reduced wall thickness and structural integrity.

The Siberian larch black cladding and grey wood decking forms a strong dark exterior palette that contrasts with the lighter colours of the interior, which is flooded by natural light from the two skylights. The bi-fold doors and sliding windows provide a fully openable area, uniting the interior and exterior for warmer days. The BBQ brickwork connects with existing materiality of the house. It creates a subservient relationship while emphasising the contrast of the black box.


  • Begun: Sep 2018
  • Completed: Nov 2018
  • Floor area: 13m2
  • Sector: Residential
  • Total cost: £28,000
  • Funding: Private
  • Tender date: Jan 2018
  • Procurement: Self Build
  • Address: 23 Heathway, London, SE3 7AN, United Kingdom

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