The Peterborough EnviroCluster Retrofit Project is one of eighty seven social housing projects across the UK which benefitted from a share of £17 million of government funding to test low carbon building technology. The programme, entitled ‘Retrofit for the Future’, was the first of its kind in the UK, and saw social housing units across the country retrofitted with new, innovative technologies. Understanding and implementing best practice retrofitting is key to meeting the government’s CO2 reduction target of 80% by 2050. The results of the projects will be shared to help show how the UK’s current housing stock could be made more energy efficient.
The retrofit prototypes each received an average of £142,000 to demonstrate deep cuts in carbon emissions and exemplar energy efficient measures in UK social housing. The level of funding is specifically designed to stimulate the implementation of innovative, proof of concept demonstrator houses that may offer cost effective solutions for wider role out across the UK. Each demonstrator house will therefore be carefully evaluated by the Energy Saving Trust for at least 2 years and the potential for lower cost implementation in volume across the remaining UK social housing stock assessed.
The UK Centre for Economic & Environmental Development (UK CEED), in partnership with Peterborough City Council led a successful bid which won £150,000 of funding to retrofit a property in Peterborough with a consortia of local environmental businesses from theEnviroCluster. It is one of 87 such projects awarded funding out of 190 which originally applied.
Working with Axiom Housing Association, a 1970’s/80’s masonry construction, two story, three bedroom, 76m2 end terrace house was chosen to be retrofitted. The property had trench fill foundations, a concrete ground bearing floor, a timber joist first floor, a trussed rafter roof space and a concrete tiled roof. There is a cavity wall construction with brick outer leaf, concrete block inner and additional tile hanging to first floor to 3 elevations, the house is plastered internally and has low-mid performance double glazed PVCu windows.
The original proposal for the property was to create a new envelope around the existing building by externally insulating to achieve higher U values for both the external walls and roof. Some 200mm of rigid insulation board was to be added to the whole of the front and side elevations, while the rear was to have 100mm of external insulation. The rear, which is south facing, was originally proposed to have a solar capture wall in addition to the 100mm. The idea for the external insulation was to minimise the impact to the internal faces of the wall and thus minimising the impact to the occupant of number 11.
The overall air tightness of the property was to be improved and the aim was to achieve passivhaus new build standard in the core fabric elements. Air management is through a heat exchange unit situated in the roof void and was planned to utilise the solar capture wall to pre heat air in the winter before circulating around the property. This was later designed out at the pre construction stage due to the budget cost and difficulties in quantifying the energy savings through SAP modelling. In the removal of this the external insulation was increased to 200mm to match the other elevations. Air ducts are incorporated into the wall insulation to pre-heat air entering the heat exchange unit in the loft; retaining some of the initial solar passive principles.
The roof was planned to be stripped of tiling, the trussed rafters strengthened, the roof externally insulated then retiled however the fasteners needed for this proposal proved elusive and the final solution included a cut timber roof over the top of the trussed rafters. The insulation was changed from a high decrement vapour open insulation to a low k value insulation vapour closed, so vapour open roof was replaced with vapour closed construction. Heat recovered from below the roof tiles is mixed with tempered fresh air in the loft space to feed the heat exchange unit and reduce the need to heat fresh air to the dwelling.
Finally, renewable energy was proposed to provide water heating, with solar photovoltaic panels installed to reduce the amount used from the national grid.
With the exception of the Solar capture wall the overall design principles remained the same through the build, however there were certain details that were altered in order to achieve the design.
Construction work took around 8 months, with the tenant in-situ, completing in May 2011.