Bridport House case study, Willmott Dixon

UK’s largest cross-laminated timber residential scheme
Client: London Borough of Hackney
Architect: Karakusevic Carson
Specialist timber contractor: Eurban
Timber supplier: Stora Enso
Completion: September 2011
Case Study
Bridport House

Overview Bridport House is an eight-storey residential tower built for the London
Borough of Hackney. It is the first phase of the regeneration of the local
authority’s Colville Estate. The brief was for 41 socially-rented affordable
homes - the first wave of council housing to be built in Hackney for 45 years
The 1,576m³ building has two main entrances and eight front doors to
the family sized four bedroom maisonettes at ground and first floor. Above
there are 33 one, two and three-bedroom apartments, many of which are
double aspect with generous flat areas, large storage and multiple balconies
and terraces; exceeding GLA space standards.
Bridport was entirely constructed from cross-laminated timber (CLT), making
it one of the tallest residential wooden structures in the world and UK’s first
multi-storey to be entirely built of the material – including the ground floor.
The team chose CLT because of its lighter weight: a survey revealed a large
Victorian storm sewer under the site and building around a reinforced
concrete (RC) or structural steel frame would have required significant
extra reinforcement of the foundations to create a building of the
same height. Constructing with CLT was also quicker, taking just 12 weeks
on site, six weeks less than a traditional frame solution. Willmott Dixon is
probably the leading main contractor delivering CLT projects, having recently
started our eleventh of this type.
The Research Project Willmott Dixon worked with the Cambridge University Engineering
Department (CUED) Centre for Sustainable Development to calculate
the structure’s embodied energy. The team carried out a comparison of the
materials between CLT and RC frame with available data from manufacturers
and the Inventory of Carbon and Energy (ICE) database.
They found that, had the building been of conventional RC frame, an
additional 892 tonnes of carbon would have been embodied in it. This is
equivalent to 12 years’ worth of energy required to heat and light all
dwellings. When the sequestered carbon was added to the carbon avoided,
the total figure was 2,113 tonnes, provided the timber is reused. This is
equivalent to 29 years of operational energy.
Equipped with this data, the design team successfully negotiated with
Hackney Planning Department to reduce the requirement for onsite
renewable energy provision from 20% to 10%.
Experts have welcomed our research since there is a shortage of credible
information on embodied carbon. As thermal efficiency standards improve
and buildings produce less carbon in operation, embodied carbon becomes
relatively more important.

It used to be said that embodied carbon made up 10% of total whole life
emissions of a building, but it will soon represent up to 60-70%, as
regulatory requirements for energy efficiency tighten
Following this project, Willmott Dixon is again working with Cambridge to
develop a tool to calculate the embodied carbon of buildings, including the
development of a detailed life cycle analysis tool. BLP Insurance and UCL
Energy Institute are co-collaborators.
Airtight, Sound and Fireproof The accuracy of construction with CLT aids air tightness as elements such as
windows fit exactly.
The CLT boards are also edge glued, which further increases their air
tightness and means the five layer CLT boards achieve the same air tightness
as non-edge glued five layer boards. As a result, the air tightness of Bridport
House, at 3m3/m2.hr @50 pa is three times better than minimum Building
Regulations. We achieved 1.6 on one of the flats, giving us one of our best-
ever results and well below our targets.
Willmott Dixon Site Manager
Terry Waite: “I love building with CLT. It’s fast and simple to use, as well as clean and
precise. Because CLT is factory-made and delivered to the site for assembly,
there is far less waste than in conventional construction. The workers on the
site also enjoyed working with prefabricated timber as opposed to steel or
concrete. It is a nicer and cleaner material to work with.”
CLT is an ideal solution to the very specific issue of weight. “The large
Victorian sewer running beneath the site of Bridport House made it
unsuitable for a traditional and heavy concrete frame structure,” explains
Terry.
Housing Design Awards Winner: Bridport House in Mayor’s Housing Design award for Community
Consultation