Quick to construct with high levels of performance and durability, insulating concrete formwork (ICF) has been gaining popularity in the UK for some time. Once the preserve of self-builders, it is now being adopted by architects, housing associations, developers and local authorities for residential, education and healthcare projects. So what exactly is insulating concrete formwork, how does it work, and what are its main benefits?
ICF in practice
Nudura’s ICF system is based on pairs of 67mm-thick, type 2, closed-cell expanded polystyrene foam panels, which are connected using folding cross ties or ‘webs’ made from 100 per cent recycled plastic (HDPP). Integrally moulded into the foam at 203mm centres, the webs create hollow block forms into which concrete is cast. Standard core thicknesses comprise 102mm, 152mm, 203mm, 254mm and 300mm, although thicker cores are also achievable.
The EPS formwork remains in place after the concrete has cured, providing thermal insulation on both sides of the building envelope. Inherently flexible and design-orientated, ICF is able to accommodate 90- and 45-degree corners, brick corbel forms, brick corbel extensions, T-form units, double-taper top forms and factory-cut radius forms.
ICF is inherently flexible and can accommodate many different forms
Energy efficiency and acoustic performance
One of the principal benefits of insulating concrete formwork is its energy efficiency. The thermal mass derived from the 67mm-thick EPS panels allows Nudura’s standard, 0.24W/m²K U-value-rated wall assembly to perform to the equivalent of 0.16W/m²K. U-values of 0.21, 0.18, 0.14 and 0.12 are also available. The latter allows building owners to reduce their annual energy costs by up to 70 per cent.
Solid concrete wall construction of this type also ensures good levels of airtightness – as low as 0.33m³/hr.m² or 0.18 ACH – and superior thermal bridging performance. This results in even temperatures throughout the structure with reduced draughts and cold spots. Furthermore, the manufacturer provides a wide range of thermally modelled junctions based on British Building Regulations and the Passivhaus Planning Package (PHPP).
The high mass of ICF construction also means that it acts as an effective sound barrier, dampening unwanted external noise. A typical 152mm concrete core and form attains an SRI performance of 51dB DnTw + Ctr when tested to NF EN ISO140-1 (1997). According to the manufacturer, this can be easily adapted in the field to achieve an SRI performance of 71dB or higher.
Fire performance and disaster resistance
The combination of 152mm-thick steel reinforced concrete and non-toxic, fire-retardant expanded polystyrene foam provides four-hour fire resistance when tested to ISO834-4:2000 or BS EN1365-1:1999. Walls are highly impact resistant and can be designed to withstand hurricane conditions up to 350mph. The company provides structural tables for basement walls, above ground walls and lintels in line with Eurocodes 2 (concrete structures) and 8 (seismic). ICF-based buildings are also resistant to water ingress due to the non-absorbent properties of the EPS foam.
Insulating concrete formwork is suitable for a wide range of projects from residential to schools and offices
Durability and mould-resistance
ICF structures are designed to last and retain their value for longer. Reinforced concrete can provide better durability and reduced repair and maintenance over its lifetime compared to some timber structures. Meanwhile, EPS foam does not propagate mould growth and passes all fungi resistance testing.
Speed of construction
The speed of assembly for ICF walls can reduce both construction times and the number of subcontractors needed on site. Nudura ICFs are typical installed at a rate of 0.5 man-hours per square-metre. The system can be assembled and cast in all weather conditions.
For more information on Nudura ICF systems please visit the website.