John Street Banner

Transformation of a beautiful Georgian town house into an energy efficient home


Project Profile


retrofitting, enerphit and passivhaus

Selectaglaze has assisted Prewett Bizley Architects in the transformation of this beautiful Georgian house into a comfortable, peaceful and energy efficient home. This Grade II Listed property built between the 1790s and 1840s of a timber frame construction is situated within the heart of leafy Bloomsbury. John Street Facade Typical Georgian facade Prewett Bizley Architects were commissioned to retrofit the property to EnerPHit or near EnerPHit standards. These award winning architects are experienced in retrofitting Listed buildings to a high level of energy efficiency whilst retaining the property's original character. Windows are one of the key elements of the Georgian architectural style. The large single glazed sash windows were a particular challenge as they represented a significant proportion of the wall area and could not be replaced. Secondary glazing proved the only acceptable adaptation to this period property. The extremely high levels of insulation required, the aesthetics and the need for working shutters in some rooms demanded a bespoke solution. Robert Prewett approached Selectaglaze and originally proposed a totally new design but coincidentally the company was both developing a new sash window design and trialling Pilkington’s Spacia thin vacuum units which have a centre pane U-value of 1.0. The resulting Series 25 window proved perfect for the project as it offered high sealing efficiency, a very low U-value and a discreet frame with a specially developed slide catch that allowed shutters to fully close.  The resulting retrofit achieved an air tightness of 1 air change per hour. Comprehensive monitoring is currently being recorded over time in order to assess whether the project has achieved Enerphit standards.