Considering the abundance of aged homes in Britain, and the emergence of UK-based designers and builders with energy efficiency mind-sets, there are bound to be retrofits that test the practical limits of what can be done to improve the performance of a building that is really, really old.

One such project completed two years ago – an upgrade of a 140-year-old Victorian known as Grove Cottage, in Hereford – was certified under Passivhaus Institut’s refurbishment standard, known as EnerPHit.

A look at the UK-based Sustainable Energy Academy’s Old Home SuperHome Project, though, tells you that Grove Cottage, while still unusual, is hardly unique. The project is not unlike the retrofit of another 1870s-era Victorian undertaken as part of the Retrofit for the Future competition. That contest was hosted by the UK’s Technology Strategy Board, a government-appointed group of executives whose mission is to stimulate innovation in areas that will encourage growth and productivity. The retrofit team on that project managed to insulate and air-seal the London home to meet Passivhaus performance requirements (a pressure test showed 0.49 air changes per hour at 50 Pascal pressure difference) while also complying with guidelines for historic preservation.

A low-carbon target

Members of the team behind the Grove Cottage transformation, which included architecture firm Simmonds Mills and builder Eco-DC, said they followed principles prescribed by the Passivhaus standard and by the CarbonLite program, an initiative developed by the Association for Environment Conscious Building, which promotes construction of energy efficient buildings in the UK.

CarbonLite includes three performance standards: Silver, representing a reduction of carbon emissions by 70% “compared to the UK average for buildings of each type”; Passivhaus, which typically provides a carbon emissions reduction of about 80%, according to the AECB; and Gold, a standard that provides 95% carbon reduction through a combination of Passivhaus design and renewable-energy equipment.

Grove Cottage is of the same vintage as the Retrofit for the Future project, and both buildings feature brick exterior walls. On the cottage, the walls and roof were insulated with PermaRock expanded polystyrene (250mm on the walls, 400mm on the roof). Floor joist bays were filled with sheep’s wool insulation. The average annual cost for heating, cooking, and hot water in building, which also is equipped with a solar hot water system, is about $380, the Simmonds Mills website notes.

We’ve asked the owner of the building, Simmonds Mills principal Andy Simmonds, for more details about the project, including its final cost.