• Client: Private
• Architect: Tsuruta Architects
• Photography: Ståle Eriksen
• Completion: 2019
• Value: Confidential
• Size: 19 m²
• Expertise: Structures

Wooden Roof is part of a Grade II listed end of terrace property situated in the heart of Islington. The client wanted to replace and extend an existing lean-to conservatory at the rear of the property with a new space that took advantage of the strong afternoon light that entered the north facing garden.

The new conservatory is clad in planks of charred wood and sunk within the garden, measuring approximately 5.5m x 3.5m. The apex of the roof is kept below the existing garden wall to prevent it from imposing itself on the neighbouring properties.

Typically, conservatories are formed with steeply pitched roofs to let as much light as possible into the room. However, due to height restrictions this form was not possible on this site. Instead, we worked closely with Tsuruta Architects to develop a shallow timber diagrid roof, derived from the lines of the site boundary, that supports glazed roof panels allowing light to flood into the room. The timber roof beams are fabricated with a saw-toothed ridge that creates facets in the glazing, allowing rainwater to run off to the perimeter drainage channels whilst minimising the overall height of the structure. The deep beam profiles act as brise soleil, reducing the heat gain within the building, and cast palpable shadows into the space. In order to reduce the depth of the roof and maximise headroom within the height restriction, the timber was left exposed acting as both the structure and a decorative finish.

We took full advantage of the natural structural capacity and low thermal conductivity of wood. The entire conservatory, from the roof, to the window and door, was made from the same species of acetylated wood components, which is known for its durability and dimensional stability. To achieve the high level of dimensional accuracy required for the joinery all the timber elements were prefabricated and cut using a 5-axis CNC cutting machine.

This enabled the planned roof falls to be installed correctly and easily on site which also minimised off-cuts and wastage. Digital models of the structure, which were used by the fabricators, ensured that a neat fit at complicated junctions could be achieved and ensured that when on-site the components fit together easily.

For this project, the decision was made to use Accoya® which is an acetylated softwood. Externally the wooden faces are fully exposed and charred, using the traditional Japanese method of Yakisgui, to protect against moisture, insects and rot. The treatment allows the wood an extended durability life in exposed uses of up to 50 years.

Re-using the existing concrete slab, using timber as the main structural material and eliminating the need for extensive finishes meant we were able to minimise the embodied carbon of the structure keeping it to a total of 156 kgC02e/m2, allowing the whole building to come in below the RIBA 2030 targets.