Complementing the best practice articles on the design and construction of insulating concrete formwork, Nudura highlights key aspects of its ICF systems through two case studies

Case Study One
Project: Curly House, West Sussex
Architect: Ecotecture 

Curly House by Ecotecture replaces an old, poorly extended and thermally inefficient dwelling located within the Sussex Downs Area of Outstanding Natural Beauty. Designed to Passivhaus principles, the crescent-shaped, 408-square-metre building is cut into its sloping site, with the upper level sliding partially over the lower one.

After considering various sustainable construction options, the project team specified Nudura ICF walls and a thermally-broken, super-insulated deck system for the floors and roof. This combination was felt to give the best performance in terms of thermal efficiency and airtightness. The insulating element of ICF acts as a buffer to the thermal mass, allowing the slow release of heat and ensuring a constant internal temperature throughout the year. The partially buried nature of the design also favoured ICF construction over timber and steel.

Architectural technician Jake White (formerly of Ecotecture), sites ICF’s flexibility as one of its most appealing aspects. “The design started out with lots of different radiuses”, explains White, “but we refined and rationalised it until we had just two. The fewer types of blocks you procure the better, from a cost perspective.”

Following installation of the EPS forms, vertical and horizontal rebar was added to the structure. Lintels were designed to be poured in-situ and are made up of rebar saddles. Steel beams were used only to frame the stairwell. “The concrete core’s structural strength was an advantage when adding features such as the brise-soleil”, explains White. “This was bolted straight on. If you were adding an overhang to a timber-framed house, you might need a steel frame to provide primary support, which has the potential to create thermal bridging, as well as movement and cracking.”

Initial air tests for the scheme indicated 0.2 air changes per hour – surpassing the 0.6 ACH standard required for Passivhaus compliance – while predicted heat demand (evaluated using IES thermal analysis modeling) is 3kWh/m²/year. It performs at 1.5kWh/m²/year Compared with an average UK home (in 2003), the Nudura ICF system reduces energy demand by 98 per cent. Following completion, the house’s occupants reported that they did not use the heating system throughout the winter of 2011/12.

Case Study Two
Project: Inclusive Learning Campus at Woodside High School, London
Architect: Penoyre & Prasad

Designed by Penoyre & Prasad, the Inclusive Learning Campus at Woodside High School in London is a £25m project incorporating both refurbishment and new-build elements. Nudura’s ICF system was chosen for the latter for reasons of design flexibility, energy efficiency and speed of installation. Project engineer, the Clark Smith Partnership, was also impressed by the product’s loadbearing capacity, lateral wind-resistance and ability to accommodate large structural openings.

Minimising disruption to the school during construction was essential. The ICF forms enabled the two-storey buildings to be made watertight quickly, which in turn allowed the interior fit-out to commence six to eight weeks earlier than with conventional blockwork construction. Furthermore freezing site conditions did not delay the project, as the system can accommodate concrete pouring in temperatures as low as minus 30 degrees C.

The project employs 150mm-thick C30/37 concrete walls sandwiched between permanent 67mm-thick EPS forms. “The Nudura system is well thought through and fits together using special corner pieces”, explains Terry Smith, director of the Clark Smith Partnership. “The company’s propping system, with its integral working platform, is simple and efficient.”

Last but not least, the inherent flexibility of the ICF system allowed the architectural features of the school’s existing buildings to be replicated with comparative ease where required. The completed project provides energy efficiency and airtightness levels that are much higher than those associated with traditionally constructed education buildings.

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