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HOOLA precast balconies a team effort from Schöck and Thorp

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Tidal Basin Road in East London, gateway to the soon-to-be regenerated Royal Victoria Docks area and a short stroll from the Excel Exhibition Centre, is now home to a new twin tower glass-clad landmark building – the 'HOOLA'. This £80m development has transformed a brownfield site into two rippling 23 and 24 storey glass towers, that offer 360 apartments with a mix of studios, along with one, two and three-bedroom units. All apartments have floor-to-ceiling windows and sliding doors with balcony access. The residents also benefit from a range of facilities on-site, including a gym, business lounge and concierge services. The buildings effectively sit on a 'landscaped lid', which covers the single level basement accommodating parking and refuse plant spaces. The scheme then uses bioengineering technologies to establish a series of soft landscape terraces. These wrap around and conceal a basement car park, along with groups of trees, which enclose a residential garden.

The buildings are super-insulated and the concrete frame will act as a heat sink – absorbing heat on warm days and releasing it back into apartments when it cools. An innovative link-up with the neighbouring ExCel Exhibition Centre will also see excess heat piped directly into the two towers. This will provide all the necessary heating and hot water requirements and significantly reduce maintenance costs by doing away with the need for individual boilers. A critical design requirement for such a super-insulated building was the avoidance of any risk of thermal bridging at the many concrete-to-concrete balcony connectivity points – so highly efficient structural thermal breaks were required throughout. The preferred solution was the Schöck Isokorb type K for cantilever balconies. With its innovative HTE pressure-bearing module and Neopor® core, the unit provides extremely high thermal resistance; and is also a load-bearing element which transfers bending moment, stress and shear forces.

Complex balcony detailing for Thorp Precast

The balconies on the HOOLA, which are all precast in a Reconstituted Portland Stone Concrete, meant that thermal break suppliers Schöck had to work closely with specialists Thorp Precast of Newcastle-under-Lyme. Luke Smerdon-White, Technical Director at Thorp, takes up the story: "We had to design, manufacture and deliver 1410 precast concrete balcony sections that had to then be cast integrally with the in situ concrete structure. The design and detailing coordination on our part was taken from the 2D consultant's information, which we converted into 3D Tekla modelling". "The balcony detailing is complex. The exposed front-face is curved, with almost 50 different dimensional configurations, while the internal face has a facetted line that had to correlate with the glazing line and opening doors. The ability to integrate the Schöck Isokorb thermal breaks using 3D BIM details was critical; as we had to both accommodate the slab and column reinforcement – and achieve the finite positioning of the connection modules for structural and cost efficiency. The logistics involving deliveries was challenging too and involved 235 articulated lorry journeys over a 58 week period, all on a just-in-time basis".

On super insulated buildings, balcony insulation is especially critical

Research at the Oxford Institute for Sustainable Development (OISD) at Oxford Brookes University shows that as a result of airtightness and fabric U-values being improved in UK building, thermal bridge heat losses are responsible for an increasing percentage of the overall building heat loss. It is common for thermal bridges to account for 20% - 30% heat loss in multi-residential units (as calculated by thermal modelling) and balcony connections can be a major contributor to the thermal bridge heat loss if effective thermal isolation is not included in the design. Schöck offers a number of highly effective solutions to various thermal bridging situations. In addition to concrete-to-concrete capability, the Isokorb range provides totally verifiable solutions for concrete-to-steel, steel-to-steel and even a maintenance free alternative to wrapped parapets. All solutions meet full compliance with the relevant UK building regulations and offer BBA Certification and LABC Registration. The requirement that the temperature factor used to indicate condensation risk (the fRsi value), in residential buildings, must be equal to or greater than 0.75 is comfortably met by incorporating the Isokorb. It also complies with the Government Standard Assessment Procedure, SAP 2012, concerning CO2 emissions from buildings and respectively heat losses through non-repeating thermal bridges. The lambda values of the Isokorb enable energy loss to be reduced by as much as 84% to 91% in various connective situations.

For a free copy of the Schöck Thermal Bridging Guide and / or the Thermal Bridging Solutions brochure – contact the company on 01865 290 890