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A new-build provides the best opportunity to achieve an energy efficient building. However the grey clouds gather over existing building stock as it is from among this rubble the phoenix needs to rise: 40% energy use in the UK is attributed to buildings already constructed (in accordance to the government – see here for link).

The technical difficulties of retrofit of alternative energy technologies and fabric performance have been raised by Progressive Heritage in the past – see the post from the Ecobuild conference. Technical difficulties such as thermal bridging and u-value calculations of existing fabric become harder to control in heritage buildings – where typically the fabric relies on breathing to control moisture.

Passivhaus is a technical approach to reduce energy use – simplistically creating an air-tight building in conjunction with highly controlled ventilation. The challenges of an existing building, particularly those pre-1919 – ie: solid wall construction – lead to the development of the EnerPHit certification by Passivhaus launched in March 2012.

The Green Building Company completed a barn conversion, Stirley Farm, using the EnerPHit benchmark in March 2014. A great blog by Director Bill Butcher details the construction developments and can be accessed here. The principle of the rennovation is summarised as a ‘box within a box’ to achieve the Passivhaus goals.

What of listed buildings where the approach of a box within a box to achieve air tightness would turn its back on historic details? A Grade II listed house in Clapham has recently achieved the Silver Standard in the CarbonLite programme by the Association for Environment Conscious Building. Click here for more information on the standard. The approach by the AECB here is to accept that high air tightness levels can often only be achieved by an invasive approach[1]. The AECB states the adoption of the Silver Standard for refurbishment, ‘…could achieve CO2 emissions reductions of around 70% compared to a standard building’. The scheme used over 9 types of insulation material – the full case study can be accessed here.

The Silver Standard seems a more realistic and sensitive approach which may be appropriate for some listed buildings to adopt in looking to achieve a recognised energy improvement standard. It will be interesting to follow case studies using this standard in future posts.

[1]The scheme at Lena Gardens was the first in a Conservation Area to achieve the Passivhaus standard. The case study illustrates the degree of reconstruction required there that would be unlikely to be achieved on a listed building. Click here for a link to the case study via Pinpoint.