With 26% of building heat lost through windows & 45% of the total UK energy consumed for heating purposes, efficient windows have the potential to significantly reduce energy consumption & in turn greenhouse gas (ghg) emissions, thus supporting EU & national targets to reduce ghg emissions by 80% by 2050. Energy efficiency of windows is measured by U-value, lower U-values=higher thermal resistance & improved efficiency. The rising price of fuel & Government regs/initiatives, is driving consumer demand for windows with lower U-values. Double glazing is the most commonly used system, installed in 42% of EU buildings. Aluminium & uPVC double glazing is preferred for commercial projects due to competitive price but: 1. Does not achieve U-values = 1.4 W/m2.K required by forthcoming 2014 Building Regs 2. No single system meets the criteria demanded by UK architects & specifiers crucial for mass penetration of commercial mkt Current best in class systems meet energy requirements & aesthetics but are high in price (triple glazing & pultruded glass reinforced plastic (GRP)) so limiting penetration of commercial glazing mkt & restricting use to high spec. projects. Viridis aim to address this mkt opportunity through the development of an innovative double glazed window which combines GRP & renewable sourced softwood, to develop a highly efficient system with: low U-value; Passivhaus standard & Code for Sustainable Homes Level 6; low price; slim profile with high glazed area; low maintenance; extensive lifespan of 60+ yrs; & internally beaded. Virdis will develop 3 glazing system prototypes, with the aim of creating a window that has the same U-value as triple glazing but can be sold competitively at double glazing price. The benefits are considerable given that replacing existing BRFC A rated windows with the Viridis system would achieve an annual energy saving of 0.4 MtCO2e/household, widespread uptake of this solution would save an estimated 8,700,000 MtCO2e/year.