Ultra low U-value walls for low-carbon-dioxide homes

This paper describes various walling systems capable of providing an ultra low U-value wall construction for use in a domestic application. The target U-value is 0·11 W/m2K −36% less than the minimum requirement for the German ‘Passivhaus’ standard and some 60–70% more onerous than current UK building regulations; this value was chosen because of the high degree of challenge it presents whilst remaining technologically achievable. The paper briefly discusses whether static U-value is truly relevant to most domestic applications in the UK, or whether it is the less understood dynamic U-value that should be the focus of attention. The positive and negative characteristics, including wall thicknesses, embodied energy, toxicity, expected lifespan and ease of installation, of various systems are discussed. Test data provided by manufacturers to support U-value claims are carefully examined. The walling systems discussed cover a broad range of technologies, including structural insulated panels (SIPs), vacuum i...