About The Building
Wenlock Road, situated within the London borough of Hackney, has taken cross-laminated timber (CLT) to new heights. Holding the title of the tallest CLT residential building in Europe at the time of construction, the 10 storey development houses 50 one, two and three-bedroom apartments. All apartments were sold off-plan prior to completion, together with 1,190 m2 of commercial units.
The Brief
Timber technology was the preferred core structural component for the build, due to Hackney’s commitment to creating more sustainable buildings. A complex hybrid CLT and steel structure was vital in creating the most efficient and sustainable structural solution for the buildings unique ‘twisted’ design - the first of its kind. The innovative ‘cross’ floor plates, which rotate on alternative floors, created complex geometry that did not lend itself to being built purely in timber, therefore a steel frame and concrete core were paired with the CLT. The steel frame was used to take the gravitational load of the structure, which was transferred on alternative levels as the floor plates twisted. The floor plates then act as a diaphragm to transfer stability forces from facades to the full height concrete core in the centre of the structure.
The twisting cruciform plan, described by Hawkins\Brown project architect, Alex Smith as 'more than a mere architectural whimsy’ - ensures that all flats are corner units, allowing them to have at least dual and in many cases triple aspect views over the city or along the picturesque Wenlock Basin.
Key Challenges
The project pushed many boundaries in terms of height, complexity and method of construction. There were concerns that pushing the boundaries on so many fronts would reduce the final performance (acoustics and thermal) of the individual units, it was therefore decided in the very early stages, to reduce that risk and construct one of the apartments on an accelerated programme, to eliminate these concerns.
The test apartment was over performing on sound insulation so it was decided that the layout of internal lining could be adjusted to meet the criteria for the building. Another area of concern was that previous timber developments had been subject to criticism due to being poorly insulated. Architects Hawkins\Brown applied in-depth research to overcome this potential issue. The research carried out within the test apartment provided conclusive evidence to support the final insulation specification leading to an insulation layer being applied under the flooring to help retain warmth in the apartments.
The client, Regal Homes, was also concerned about sustainability. Cross-laminated timber is clean to use with little onsite waste, and it is made from readily available, renewable softwood which contributes positively to high BREEAM and Code Ratings. As Wenlock Road is the first building of its height to be constructed from timber in Europe, it exploits sustainability factors that brick and mortar buildings are not able to provide.
The Solution
The benefits of cross-laminated timber are numerous - from reduced loading on foundations and infrastructure services, to impressive thermal, acoustic and airtightness performance, but most importantly, a CLT construction solution provides cost and programme certainty. The CLT was manufactured offsite, allowing exceptional levels of accuracy and ensuring minimal defects. This improved construction and project delivery timescales, reduced costs and maximised efficiency on all levels. With cost and time certainty being a crucial factor for this project, the use of CLT eliminated any risks, as it was manufactured in controlled factory conditions.
CLT wall and floor panels up to 200mm thick and weighing up to four tonnes, were delivered to the site with all openings pre-cut, allowing them to be lifted straight into position. The number of lifts required were also reduced as the prefabricated wall panels were produced up to 12m in length, therefore individual panels were able to span the entire length of the structure. This saw a reduction in the onsite lifting works which helped with the close proximity of the site to adjacent properties and site restrictions; however methodical delivery programmes still had to be sequenced to ensure just in time deliveries were maintained. As follow on trades started work on the lower floors whilst the structure for the upper storeys was in construction, meticulous planning was needed across all teams and throughout the supply chain. This was especially relevant since there was only room for a single trailer or van delivery.