Social housing supplement Retrofi t
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ECD Architects is aiming to slash carbon emissions from a 1915 home in a conservation area, using the lessons learned from a previous refurbishment. Architect Mark Elton reports
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CD Architects is helping to kickstart the retrofi t revolution in Britain by refurbishing a 1915, end-of-terrace two-bedroom house in Eltham, a conservation area in south-east
London. Working with partners Hyde Housing Group and repairs and maintenance contractor, Mears, we aim to cut carbon emissions by 80 per cent compared to the level produced by a UK dwelling in 1990. As part of the Technology Strategy Board’s Retrofi t for the Future competition, Retrofi t & Replicate II is our second pilot study addressing the technical challenges of low carbon retrofi ts, with works scheduled to begin this month. In our fi rst pilot, we used insulated over-cladding
solutions, but we knew they were never going to be appropriate here, where even door and window styles are restricted. Nevertheless, reducing heat loss from the building fabric is the main priority for any serious retrofit scheme, so internal wall insulation (IWI) was a necessity. Standard IWI solutions rely on high-performance insulation laminate boards, such as phenolic foam. This method was used in our fi rst study, the Mottingham project, but in that case the property had cavity walls, thus avoiding the condensation risks.
Insulation
For this solid-walled property, we will be installing a woodfi bre insulation lining board called Pavadentro, specifi cally designed to allow the building fabric to ‘breathe’; when working with older buildings it is important to consider air vapour transfer through the building fabric. The product slows water vapour diffusion and relies on its hygroscopic and capillary characteristics to return moisture back to the room as conditions permit. One drawback with woodfi bre for
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very low carbon retrofi t schemes is that the maximum board thickness of 100mm can only improve a solid brick wall’s U-value from 2.54 W/sq m K to around 0.33 W/sq m K, whereas the Mottingham retrofi t achieved 0.15 W/sq m K. Floor insulation will be added using woodfibre products laid between and above joists, whilst cellulose insulation will be blown into the loft space to a depth of around 400mm to achieve a U-value of 0.11 W/sq m K.
Heat loss
Windows and doors in older properties are a major source of heat loss and their improvement with higher performance products becomes essential. In Mottingham, there were no restrictions on window design so triple-glazed, highly insulated NorDan windows were installed throughout with a typical centre pane U-value of 0.7 W/sq m K. The restrictions of the conservation area, however, meant that this time around, innovation had to be integrated into a six-light timber casement window that would satisfy the planning controls. Our solution was to incorporate Pilkington’s ‘Legacy’ vacuum glazing, which achieves the same performance as double glazing within the same dimensions as single glazing. An almost invisible 20mm grid of micro-spacers within the unit keep the glass surfaces 0.2mm apart, giving a keep pane U-value of 1.4 W/sq m K for a glass thickness of only 6.5mm. To enhance the thermal performance at night, insulating Roman blinds have been sourced. Air leakage is another signifi cant heat loss factor
in older properties, but airtight refurbishment can be achieved through a combination of detail design experience and site rigour. Although on Retrofit & Replicate 1 we managed to reduce the air leakage rate to 5.6 cu m/h from 9.2 cu m/h, our approach this time
“Air leakage is a signifi cant heat loss factor in older properties”
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June 2010 CIBSE Journal
15
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