A Georgian townhouse is remodelled to meet the highest energy performance standards

An historic Listed Georgian townhouse in London’s Bloomsbury has been transformed into a comfortable, peaceful and energy efficient home that approaches Passivhaus EnerPHit standards.

This was achieved by using modern insulation techniques including an advanced secondary glazing system from Selectaglaze that markedly improves the performance of the traditional, single glazed sash windows.

The client wished for a home that used as little energy as possible and offered the most comfortable environment. Robert Prewett of Prewett Bizley architects took on the challenge of convincing conservation officers that a Grade II Listed building could be fitted with energy saving measures whilst respecting all the historic features.

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. With the high levels of insulation that were required along with the need to keep the shutters working in some of the rooms, a bespoke solution was required.

Robert approached Selectaglaze who 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 house now has air tightness close to 1 air change per hour at test pressure which demonstrates that the secondary glazing is performing very well.

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