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We did what we could realistically do to future-proof each home

lifestyles. External insulation was applied to walls where practicable. When this was not the case, for example on dwellings in conservation areas, 60 mm-thick Kingspan Kooltherm K18 insulated dry-lining plasterboard was added to the external walls internally. In addition, 300 mm insulation was

installed in the loft and 100 mm beneath the suspended timber ground floor. ‘The focus was on improving the fabric energy efficiency of the building, to provide our residents with a good quality, energy efficient, refurbished home,’ says Bush. In terms of services, the whole-house refurbishment involved the removal of all wall-hung gas fires and electric heaters. These were replaced with an energy efficient, gas-fired central heating system incorporating an A-rated condensing boiler and thermostatic radiator valves. The

building’s entire electrics were also replaced and, where appropriate, low-energy light fittings installed. Replacement double-glazed windows

were also fitted. Where a home was in a conservation area, identical double-glazed timber replacement sash windows were installed. Additional sound insulation was also added to the separating walls and floors of flats. The kitchen and bathroom was stripped out and replaced. ‘We did what we could realistically do to future-proof each home,’ explains Bush. The works were carried out by contractor

Case study Funding supports Passivhaus project

Metropolitan Housing Trust London’s Neighbourhood Investment Unit (NIU) was successful in its bid for funding under the Technology Strategy Board’s Retrofit for the Future projects. The London project, at 10 Hawthorne Road, aimed to take the NIU’s existing approach to renovating an Edwardian, mid-terrace property located within a conservation area and expand on it by implementing a Passivhaus- style, super-insulated, super- airtight retrofit to achieve an

Element Front wall Party walls Rear walls

80% carbon reduction. The project was completed in December 2010 and is being monitored by University College London The house was originally

built as two separate flats but it will be converted into a single home under this project. The scheme comprised solid brick external walls, a suspended timber ground floor and an un- insulated loft. The original sash windows had previously been replaced with uPVC windows, which had been fire damaged.

U-value w/m2K Retrofit solution 0.21

0.31 0.15 Ground floor 0.18 Loft Windows Airtightness

Heat recovery ventilation

Top-up heating

0.11 0.75

MHP worked with Anne

Thorne Architects, services and structural engineer King Shaw Associates, and contractor Sandwood Design and Build, to develop an air-tight scheme with high levels of insulation. The Passivhaus Planning

Package was used to model the existing house to enable the design team to study the effect of different insulation, ventilation and heating solutions. The main elements of the

retrofit solution are shown below.

The house was in a conservation area so the front elevation was insulated internally

The walls were insulated to prevent heat being lost to neighbours

High levels of external insulation added

Existing timber floor replaced by a new insulated ground floor slab

Sheep’s wool insulation laid over the existing ceiling joists Triple glazed timber windows

A draft-free layer is formed from a continuous layer of internal plaster linked to building membranes within the walls, ceilings and floors

A mechanical heat recovery ventilation system supplies clean air to the living areas and extracts from the bathroom, and kitchen

Heat is provided by the occupants and their electrical goods. A small amount of additional heat is delivered with the fresh air, while small radiators fed from the hot water tank provide heat when it is very cold

Hot water is provided by a gas boiler with integrated, roof- mounted solar thermal panels

Apollo Property Services Group, under a partnership agreement. Having an in-house team and partnering with a contractor has ensured programme flexibility and consistency of service delivery on such a complex series of projects. This arrangement has been so successful that programme time has reduced from the initial 14-week refurbishment programme to 12 weeks, with a corresponding reduction in costs. According to Bush, initially costs were

typically £60,000 per home. However, cost savings and programme efficiencies have helped drive this down to £50,000 per home. ‘In addition to minimising inconvenience to the residents, the time and cost savings enable the Trust to refurbish more properties with the same budget,’ he explains. To help residents get the best out of

their newly refurbished home on their return, MHT London provides them with a simple manual that explains how to use the heating system efficiently and gives other energy saving advice. ‘You can do a fantastic refurbishment but you need the residents to make the best of the designs to realise the benefits fully,’ says Bush. Funding for the programme is mainly

through MHP’s own reserves, topped up with grant funding through initiatives like the Carbon Emissions Reduction Target (CERT), where these are available. To date the programme has carried out more than 300 of these refurbishments at a rate of about 60 a year. Typically these achieve a SAP rating of 80, with primary energy use at 164 kWh/m sq per year, and carbon emissions of 2.3 tonnes per year. For the residents, this equates to typical annual fuel costs of around £457. What’s more, from the MHP’s

perspective, once the properties have been refurbished, day-to-day maintenance costs are reduced.

46 CIBSE Journal June 2011

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