With the help of insulation from Kingspan, a Victorian three-storey terraced house in a Holland Park conservation area in London has become the first UK retrofit certified to Passivhaus standards. <br> <br> Two layers of Kingspan Thermawall TW55 insulation were installed, one on either side of the OSB air-barrier. Thicknesses of 150mm and 50mm of TW55 were used on the external walls. Together with the 12mm OSB this achieved a U-value of 0.1.<br> <br> The ceiling on the top floor had 150 mm Kingspan Thermawall TW55 between the joists. The joists were underscored with OSB followed by 50mm Kingspan Thermawall then 12mm plasterboard. The floor over the cellar was formed by two layers of OSB with 150mm Kingspan Thermawall TW55 between them. <br> <br> With a thermal conductivity as low as 0.022, Kingspan Thermawall TW55 allows relatively thin layers of insulation to deliver very low U-values. Its closed cell structure renders it highly resistant to moisture ingress and delivers reliable thermal performance for the lifetime of the building.<br> <br>