Our retrofit model evolved to include a combination of Passivhaus, Minergie and Active House principles. The Active House standard was adopted as we wanted to achieve a comprehensive retrofit to cover issues such as day lighting and embodied energy. This standard specifies targets for primary energy, indoor climate and environment and has an emphasis on occupant health and wellbeing.
A sensitivity analysis of each proposed retrofit measure was conducted using PHPP with the Trias Energetica concept employed to establish a hierarchy of measures. To prevent overheating, insulation levels were designed to suit the summer condition and took into account the predicted increase in the maximum mean summer temperature expected by 2050.
A systematic deconstruction enabled all material removed from the house to be measured to conduct a life cycle assessment (LCA). Sima Pro ISO 14044 LCA software was used to compare the embodied energy of the retrofit house to an equivalent new build.
To provide a floor u-value of 0.10 W/m²K, twenty tonnes of old floor slab and rubble were removed to allow for 200mm of phenolic insulation under the new concrete slab. To reduce thermal bridging, 30mm of phenolic edge insulation was fitted against the party and internal walls and 120mm against the external walls.
Some walls had been partially dry lined in 2001 using the dot and dab method resulting in a lack of airtightness between the insulation and the internal face of the brickwork. This had allowed warm moisture laden air to condense on the cold brickwork and plaster behind the dry lining, causing damage to structural timbers and creating areas of toxic mould growth. Evidence of this decay highlighted the importance of airtightness and also the warning issued by the World Health Organisation of occupant’s health suffering from “Increased exposure to dampness and mould being created by energy conservation measures that are not carried out properly”.
We found that wooden joists positioned below the dry lining were suffering from wet rot. However, in the attic where dry lining hadn’t been installed, the joists were found to be in good condition. The eventual solution was to cut the wooden joists short and slot the ends into a steel universal beam supported on insulated pads positioned within the thermal envelope.
The wall insulation strategy developed after extensive research into the impact of internal insulation on the building fabric. Various studies were considered including ones by the Fraunhofer Institute on the drying of brick walls and the National Research Council Canada on solar driven inward vapour diffusion. A siloxane based hydrophobic impregnation was applied to the exterior of the brickwork before the internal insulation was installed. To achieve an external wall u-value of 0.15 W/m²K, 120mm thick phenolic insulation bonded to 18mm oriented strand board (OSB) was fitted using thermally broken fixings. Results from moisture sensors installed at the various wall element interfaces indicate a progressive reduction of moisture content within the walls.
During deconstruction we discovered that mineral wool insulation which had been installed for around twenty five years had been pushed tight up against the sarking felt. The lack of an air gap had caused the original timbers to rot and as a consequence a new roof was required. We designed and manufacture a prefabricated roof with a high level of insulation to obtain a u-value of 0.10 W/m²K. The old roof was removed and the new roof lifted on and made weather tight within a twenty-four hour period.
The locally manufactured triple glazed windows were installed in the reveals within an insulation collar to isolate them from the surrounding brick work. To minimise heat loss and control solar gain through the triple glazed windows, thermal blinds were fitted.
To increase day lighting, four triple glazed roof windows were installed and a sun tunnel to illuminate the central stair well. The sun tunnel was modified to thermally isolate the reflective aluminium tube from the external flashing. A cassette filled with translucent UV stable aerogel insulation mounted inside the light tunnel provides an estimated u-value of 0.50 W/m²K.
The retrofit house is being subjected to a building performance evaluation to compare the predicted building performance with the measured performance. The Energy Saving Trust is monitoring energy use, indoor climate and a host of other metrics for a two year post occupancy period. Performance of the structure is being monitored using various sensors including ones for moisture and temperature positioned within the building fabric. Heat flux sensors attached to various elements of the thermal envelope will enable analysis of predicted u-values and in situ u-values.