Lewes, East Sussex
Construction Time: Three Months
Completion Date: Dec 2011
Gross Floor Area: 88m2
Contract Value: £50K + renewables
Build Rate: £579/m2 + VAT
‘U’ Values: Roof – 0.14W/m2K. Walls – 0.18W/ m2K.
Energy usage: Gas: 5600KWh; Electricity 1600KWh or 1.9 tonnes of carbon per annum.
Carbon Impact: 0.4 tonnes of carbon per annum (UK average is 5.7 tonnes)
Main Contractor: CJ Gowing and Sons.
The refurbishment of Barons Down Road, an 88m2 three bedroom terraced house in Lewes, is remarkable for having been independently verified as having a carbon footprint in use of around 0.4 tonnes of carbon per year – about 92% lower than the national average and is therefore virtually carbon neutral. The project was awarded an ‘A’ rating energy performance certificate. The net build cost was also notable at under £660 per metre squared and was optimised to take advantage of five per cent VAT on energy efficiency measures undertaken. The headline achievement of this eco-retrofit is that for around £58K + VAT the house has been made virtually carbon neutral.
The project demonstrated how important the actual choice of candidate building is to carry out an eco-retrofit. The house is a three bedroom terraced house of the Barons Down Road Estate in Lewes which was a privately developed award winning housing scheme by architects Phippen Randall Parkes from the late 1960’s using a pre-fabricated timber frame system of construction. As a timber framed house, the construction was cost effective to thermally upgrade and being of a well designed compact terrace typology with plenty of south facing glazing, the original properties were already relatively cheap to heat with excellent levels of daylighting and solar gain.
The house was bought relatively cheaply as a ‘doer upper’. The interiors had barely been touched for over forty years and needed a complete overhaul. Ian and Magali McKay devised the refurbishment on an ethos of upgrading the thermal efficiency of the fabric, refreshing the finishes and fittings but not doing any alteration work, treating this vintage sixties housing design with sensitivity and conservation in mind. The strategy allowed the owners to exploit the five per cent VAT rate for all the energy efficiency upgrades.
The estate was originally built to a very frugal specification and the walls, floors and roof had little or no insulation. The sole insulative layer for the roof and external walls was a meagre half inch timber fibre board. The ground floor slab had no insulation and no screed either. The houses do however occupy a site on a south facing slope and the original design employed a lot of glazing so the houses benefit from a high degree of solar gain. Whilst this was a benefit in winter, it is a bane for the summer months, when the super lightweight construction heats up very quickly and the top floors in particular can become excessively hot.
The retrofit strategy aimed to keep costs within justifiable limits and the build programme to a tight blast of work between purchase and occupation. Externally the houses had been refitted with PVC-U glazing and ship lap cladding and it was not justifiable to replace these elements. However, on the inside all the finishes were original and in extremely poor state, so it was decided that the internal linings to the outer walls and ceilings should be replaced and thus would allow insulating the construction from the inside. The flat roof was treated from below using a spray foam insulation between the joists. This resulted in a pseudo ‘warm roof’ and relies on a well executed vapour control layer formed beneath to work successfully. The solution also provided a very good U-Value of 0.14W/m2ºK. The walls were studded out deeper to the inside to provide a total of 150mm thickness of sheep’s wool insulation providing a U-Value of 0.18W/m2ºK.
Keeping wet trades to a minimum allowed a short build programme to be achieved. The original ground floor consisted of a power floated concrete slab with carpet on top. The ceiling heights were less than 2.3m so a floating insulation layer was ruled out. Digging out the concrete to create a deeper slab with a new insulation layer would have added up to eight weeks to the programme and unjustifiable extra cost. The solution was to cut into the concrete slab a thick layer of perimeter insulation to break the thermal bridge at the most exposed point. The rest of the floor was covered in an 8mm layer of cork which provided a modest degree of thermal isolation and a floor finish all in one. The choice of cork was also made as it is a renewable resource, harvested in fact from the tree on a cyclical basis and a fantastic form of utilising locked carbon from the atmosphere.
Utilising the latest LED lighting technology throughout keeps the overall wattage of lighting to just over 100 Watts!
The family of four moved in January 2012 and have been delighted with the results. The cork flooring laid on both the ground and first floors has proved ideal to live with especially with young children around. The house subsequently incorporated a 3KW photovoltaic array in time to capitalise on the pre 30th July 2012 feed-in tariff. Over a six month period between September 2012 and March 2013 which included a record breaking rainy autumn and a long and cold winter, the gas costs were averaging £26 per month and electricity bills at £23 per month for a family of four (not including the money back on the feed-in tariff). The dreaded summer overheating has not materialised which is probably down to the excellent thermal insulation in the roof which now is much overshadowed by the solar panels.
BBM are passionate about the need to find cost effective solutions towards affordable warmth for the Twenty-first Century. This project has demonstrated that with the right candidate of building and careful scoping of works, eco-retrofit can meet or beat the government’s target carbon emission rate for the built environment of 17kg of CO2 per metre squared per annum (in fact 4.5kg was achieved) for a sensible budget.