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Private House in Balham Meets Passivhaus Standard

A pilot project funded by the Technology Strategy Board has been set up at a typical Edwardian terraced property in Balham, South West London. The two-year project is designed to reduce the energy consumption of an Edwardian terraced property by 90% while maintaining an internal temperature of 20°C.

Housing accounts for 30% of all UK carbon emissions, so it is essential that housing stock is upgraded to be more thermally efficient if the Government's sustainability targets are to be met. However, 1-in-5 homes are regarded as 'hard to treat' solid wall constructions. Such homes are unable to improve their energy efficiency with traditional methods such as cavity wall insulation, as there is no cavity to fill.

External wall insulation systems are an obvious solution, but such measures are relatively new when it comes to housing. As leaders in the field, Sto took the opportunity to take part in this pilot project.

Local planning regulations stipulated that the front of the property had to retain its appearance. Planning for the back of the property was far more relaxed and inefficiencies to the front could be offset. Architects Prewett Bizley opted for the StoTherm Classic external wall insulation system. Applying the insulation in blocks of 289mm thick EPS was quick and easy using the Sto-Turbofix adhesive, and meant the insulation boards could be fixed directly to the old brick facade.

Adding this degree of insulation creates some technical difficulties with detailing, particularly at roof level. Older properties tend to have shallow clipped eaves that will not provide adequate protection for the extensive insulation layer. In the Balham project this was overcome with folded aluminium guttering sections attached to the eaves, removing the need for radical alterations to the roof

The windows also needed careful thought. In this case inward-opening triple glazed windows were specified, installed within plywood box linings fitted within the structural openings. Plywood linings enabled the specifiers to locate the window just outside the original face of the wall. By doing so, they aligned to the same plane as the insulation, reducing the thermal bridge at the window edge. The external insulation was also lapped over the window frame to further reduce the thermal bridges.

The windows now sit within deep reveals. To maximise daylight and sightlines, the reveals are splayed and the acrylic render used on the inner reveal is smoothed.

The U-value of the finished wall is now down to the target 0.12W/m²K. The external wall insulation is providing impressive thermal efficiency. Air tightness for the building was tested and achieved a rate of 0.8M³/hr/m²: 12 times better than current building regulations.

Due to the thicknesses of insulation used, detailing could have been a major stumbling block. The co-operation of the technical teams made sure that an attractive and cost effective solution was achieved.

The project will be monitored for the next two years to test its energy efficiency and to gather feedback from the occupants.

The Midmoor Road project in Balham demonstrates that modern energy efficiency standards can not only be met, but exceeded. In 2012, the project was entered into the AJ Retrofit awards and achieved a 'Highly Commended'.

Project Page

Private House, Midmoor Road

See the Private House, Midmoor Road project page.