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A solid brick, Edwardian terraced house in Balham has been transformed into a model of 21st Century energy efficiency, thanks to high ambitions from its owners and architects - and a little help from Kingspan Insulation.
The project (funded through the Technology Strategy Board’s ‘Retrofit for the Future’ competition, a programme to kick-start retrofitting of the UK’s social housing stock), aimed to refurbish the property to near Passivhaus standards, whilst causing as little impact to the aesthetics of the building as possible. Social housing provider, Family Mosaic, the owner of the property, engaged architects, Prewett Bizley, for the job.
Prewett Bizley is a member of the Passivhaus Trust and the company’s project designer, Robert Prewett, is a Certified Passive House Designer. He said:
“We took a very low carbon approach and the ambition was to reduce heating energy requirement, which is usually the biggest use for houses in this country. The plan was to create a highly insulated and air tight house. We set very ambitious targets for this refit and we worked very hard,building on past experience, to make sure we got the performance levels we needed.”
Energy performance targets for the programme were based on an 80% reduction in CO2 emissions from a baseline of 97 kg CO2/m².yr (typical of a 1990’s 80m² semi-detached house). Achieving such rigorous standards called for the internal fabric of the property to be stripped back, to identify and tackle potential air leakage problems. Then a continuous air tight, high performance internal thermal envelope was constructed – the key to the refurbishment’s excellent energy efficiency, according to Robert Prewett. He added:
“If it is to work, the internal lining must be continuous, otherwise it’s like wearing a jersey with holes in it – heat just escapes. You need excellent insulation and it must be very air tight, so all joints have to be taped. When specifying, we looked at the performance we required and tried to find the product best suited to those requirements. We chose Kingspan insulation for the ceilings and floors because the products were the cheapest, thinnest and best performing products for that application.”
In the first floor ceiling, just 70mm of Kingspan Kooltherm K7 Pitched Roof Board formed the base layer of the property’s continuous lining. The premium performance insulation - which, due to its closed cell structure, has thermal conductivity of only 0.020 W/m.K at 70mm thickness - was tacked to the underside of the existing timber joists, contributing to an overall U-value of just over 0.10W/m2.K.
Kingspan Kooltherm K3 Floorboard supplied the underfloor insulation for the property. The BRE Green Guide A+ rated board, which is specially designed for ground floors, was fitted between the joists of the suspended timber floors. Careful detailing contributed to the high standard of air tightness for the refurbished property and, ultimately, to a U-value for the insulated suspended floor of 0.12 W/m2.K.
The levels of success for the project cannot be fully quantified until 12 month data is evaluated. However, the signs are very positive. The house is already among the best in the UK for airtightness, with an air leakage rate of 1.3 m3/h/m2, and an 80% reduction in CO2 overall is expected.
Tenants moved in to the property in February 2011. Since then the ventilation heat recovery system has provided the sole heat source for the building, and the meagre number of radiators in the house (a heated towel rail purely for comfort and three other radiators installed as a back up in case the mechanical system’s performance was less than expected) have, according to Robert Prewett, not been used. He added:
“My prediction is that, in future, about 28 kWh/m2/yr of energy will be required for this property, which is very close to the Passivhaus EnerPHit refurbishment standard - and a molehill in comparison to the mountain of energy this type of house would normally use.”
The Balham property, like others funded through the Retrofit for the Future competition, will be evaluated over a two-year period by the Energy Savings Trust and the potential for lowcost implementation in volume across the UK assessed.