In February, United House, a social housing contractor operating in the South East and London, invited us to see a retrofit project that they have been working on with the Sustainable Energy Academy and Parity Projects. 8 Bertram Street is a typical hard-to-treat, three bedroomed Victorian terraced house – the floors and walls are solid and it has sash windows. The house was occupied by a tenant during the retrofit process so the project team needed to upgrade the building with the minimum of mess and disruption. Funding was provided by the Technology Strategy Board (TSB) which required that United House achieve a two-third reduction in carbon emissions from 60 kgCO2/m2 to less than 17 kgCO2/m2. Energy consumption was to be reduced by over 90% from 201 kWh/m2 down to 14 kWh/m2.
To achieve the required level of energy savings the project team made use of a couple of interesting new technologies, its ‘WHISCERS’ insulation system and Pilkington’s energiKare vacuum glazing. Pilkington’s energiKare system offered a way of upgrading the performance of existing single glazed sash windows to levels exceeding those of typical double glazed windows. The process involves mounting an additional 6.5mm of glass onto the window and creating a 0.2mm vacuum over the existing glazing. This lowers the U-value of the windows from around 4.8 W/m2K to approximately 1.8 W/m2K – somewhat better than a typical double glazed window’s U-value of around 0.25 W/m2K. The vacuum process left a small plugged hole in the corner of the window but we felt that this was barely noticeable.
WHISCERS, short for Whole house, In-Situ Carbon & Energy Reduction Solution, uses a laser measuring system to collect a series of data points relating to the shape of the wall. These points are fed into a computer where they can be used to trim boards of XPS insulation down to size in order create a bespoke solution specific to that particular house. At 8 Bertram Street, 112.5mm boards were used in the lounge (taking the U-value from 2.1 W/m2K down to 0.21 W/m2K), and in order to accommodate a limited amount of space, 62.5mm boards were used on the external walls in the landings (2.1 W/m2K down to 0.45 W/m2K). The initial property survey typically takes around an hour with the data handling and cutting process taking another two hours or so. Installation itself took about an hour per room and, according to the tenant, created little mess and disruption.
According to United House both the WHISCERS insulation system and the energiKare vacuum glazing cost around £5,500 each to install. To achieve the desired level of energy savings the project also had to implement the other usual energy efficiency measures, such as draught proofing, upgrading the boiler and installing solar photovoltaics (PV). In total the project came in at just over £35,000, potentially opening it up to the accusation that, as a demonstration project, it is unaffordable for the mass market. However, what was interesting about 8 Bertram Street was that United House have begun to document their projects using their new ‘Value Carbon’ approach. Value Carbon allocates a carbon value in £/kgCO2/yr for each of the different technologies being used. Some technologies, such as replacing the boiler and draught proofing have very low £/kgCO2 values of around £2/kgCO2 per annum whilst others, such as solar PV came out as much more expensive at around £18/kgCO2 per annum. United House claim that focusing our efforts on a ‘first fix’ of more cost effective measures could generate significantly more savings in the short term. For instance, they estimate that it costs around £22,000 to reduce the CO2 emissions of a single house by 70% but that, for £21,000, they could retrofit three houses for a 50% reduction. They suggest that a second fix of the more expensive measures can then be added at a later date, perhaps once technology has improved or other ways have been found to reduce our emissions.
