On a small island in the Thames, five silver-grey pyramids emerge from the surrounding trees and undergrowth, forming a linear structural rhythm that resonates with the Gothic silhouette of Eton College Chapel in the distance. At close quarters, standing in the outdoor anteroom underneath the first pyramid, the building starts to be understood as a unique construction – the walls are simply large interlocking blocks of solid cork, in which structure, insulation, external surface and internal finish are all one and the same thing.

Designed by Matthew Barnett Howland with Dido Milne (CSK Architects) and Oliver Wilton (UCL), the award-winning Cork House is an innovative and thought-provoking response to pressing questions about the materials that we build with – what are the origins of these materials, how are they fixed together to create a building, and where do these materials go when buildings die? Designed with immense attention to detail, the project is a structure of great ingenuity and beautifully reflects and respects the natural surroundings in form and construction.

The project is the latest development in an ongoing research project by Howland in collaboration with the Bartlett School of Architecture, the University of Bath, Amorim UK and Ty-Mawr. The team had been working on a sustainable construction system that depends almost entirely on cork – a renewable, resistant and insulating material that is sustainably harvested from the bark of the cork oak tree – since 2014. According to the designers, their work started with some questions about how we build today and wondering if it would be possible to develop an alternative with less complexity. In particular, they were interested in an approach that took into account environmental sustainability principles at each stage of a building’s lifecycle.

Rather than the typical complex, layered building envelope incorporating an array of building materials, products and specialist sub-systems, the Cork House is an attempt to make solid walls and roof from a single bio-renewable material. The system relies on expanded cork blocks, which are made from cork granules heated to form a solid building material. These blocks are then cut with interlocking joints to form a ‘lego-like’ modular kit of parts that can be used to self-build solid walls. Supported by engineered timber, this system negates the need for mortar or glue, and simultaneously provides structure, insulation, external surface and internal finish making it an easily recyclable and reusable structure.

It is looking upwards into the corbelled cork roof above that the total integration of material, form and construction is most legible. The resultant architectural language of pure compression is new and yet familiar – a progressive reimagining of the simple construction principles of ancient stone structures, such as Celtic beehive houses or even Mayan temples. The monolithic use of cork in place of stone adds warmth to the formal simplicity and geometric clarity. Designed, tested and developed in partnership with the Bartlett School of Architecture UCL, the team have delivered a project that is truly the first of its kind.

Internally, the exposed solid cork blocks create an evocative sensory environment – walls are gentle to the touch and even smell good, the acoustic is soft and calm, and shadows are praised as much as the quality of light. The primary use of cork is complemented by the consistent use of timber for almost everything else: black-stained Accoya for structural beams, lintels, windows and doors; bespoke furniture in cross-laminated spruce; handmade stools from English pippy oak; and floorboards in cross-sawn solid oak that are fixed with brass screws to allow for ease of disassembly.

Against the atmospheric setting created by the combination of expanded cork and timber, solid brass fittings and work surfaces create moments of richness, and copper sprinkler pipes gleam in the shade of the roof corbels. Internally, biophilic elements such as the exposed cork and oak flooring captures the light and creates a wonderfully tranquil sensory experience. In summer the skylights open to bring a sense of lightness to the space and in winter the snug interiors emanate a sense of warmth and protection.

Design research and innovation

With a focus on what is solid, simple and sustainable, the project is an inventive response to the complexities and conventions of modern house construction. Rather than the typical complex, layered building envelope incorporating an array of building materials, products and specialist sub-systems, the Cork House is an attempt to make solid walls and roof from a single bio-renewable material. Conceived as a kit-of-parts, blocks of expanded cork and engineered timber components are prefabricated off-site and assembled by hand on-site without mortar or glue – like a giant organic LEGO® system.

The house uses an evolved version of a self-build construction system developed by MPH Architects, The Bartlett School of Architecture UCL, University of Bath, Amorim UK and Ty-Mawr, with subcontractors including Arup and BRE. The research was part-funded by Innovate UK and EPSRC under the 2015 Building Whole Life Performance funding competition. The R&D process included in-depth laboratory tests for structural performance, rain penetration and fire, with two prototype structures used to establish the real-life performance of the construction system.

Whole life sustainability

The Cork House embodies a strong whole life approach to sustainability, from resource through to end-of-life and it is this ‘whole-life approach’ to sustainability that sets it apart. Expanded cork is a pure bio-material made with waste from cork forestry. The bark of the cork oak is harvested by hand every nine years without harming the tree or disturbing the forest. This gentle agro-industry sustains the Mediterranean cork oak landscapes, providing a rich biodiverse habitat that is widely recognized.

As sustainability becomes integral to all construction, this project pushes us further to look beyond the requirements and aspire to really integrate ourselves with nature. The compelling ecological origin of expanded cork is mirrored at the opposite end of the building’s lifecycle. The construction system is dry-jointed and designed for disassembly, so that all 1,268 blocks of cork can be reclaimed at end-of-building-life for re-use, recycling, or returning to the biosphere. Designed for disassembly, with no mortar or glue in the joints between blocks, all cork blocks can be reclaimed at the building’s end-of-life and even the steel screw foundations are removeable.

Alongside this simple and sustainable lifecycle narrative, the Cork House exhibits outstanding performance in relation to carbon emissions. A Whole Life Carbon Asssessment by Sturgis Carbon Profiling (to BS EN 15978) indicated that Cork House has exceptionally low whole life carbon at 618KgCO2e/m2, the lowest for any building assessed by the consultant. The WLCA by SCP also indicated that Cork House is carbon-negative at completion at -18KgCO2e/m2, with exceptionally low whole life embodied carbon at 286KgCO2e/m2 (i.e. below the RIBA 2030 Climate Challenge Target).