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Eco-renovation of an Edwardian family home

Stapleton Road, Oxford. Read about the eco-renovation of a house in Stapleton Road, Headington using internal and external solid wall insulation.

Eco-renovation of an Edwardian family home

Stapleton Road, Oxford (photos and graphs coming soon!)

We have improved the energy efficiency of our home over a number of years, with the latest changes being the most extensive – the installation of internal and external solid wall and under-floor insulation in late 2009, using ‘eco’ materials. Other eco features include: condensing gas boiler, extensive loft insulation, double glazed sash and casement windows, solar water heating, light pipe, low energy lights and appliances, wood-burning stove, some use of eco paints and finishes.

Solid wall insulation

External: Pavatex ‘Diffutherm’, 100mm – woodfibre boards, made from 95% waste soft wood. This was fitted to the side wall of our semi, which has no windows or other features. When added to 215mm brick, this insulation gives a U value of 0.33 W/m²K (0.37 also quoted in spec). This is similar to the new build standard in 2002.

Internal: Pavatex ‘Pavadentro’ – 60mm, woodfibre boards, made from 95% waste soft wood. This was fitted to the internal walls front and back downstairs, with an overlap on side walls. When this insulation is added to 215mm brick, it gives a U value of 0.54 W/m²K.

Under-floor insulation

Hemp batts – 150mm in areas with new joists and 100mm in areas with old, retained joists. U value of 150mm = 0.26 W/m²K, but value for whole floor will be greater than this (i.e. not as resistant to heat loss), due to losses around edges of floor. Hemp was chosen in preference to paper based insulation because of damp conditions. The perimeter of the floor presented some complications as the 150mm deep insulation would have touched the damp foundations. To resolve this and keep adequate under-floor ventilation a higher performance and therefore thinner insulation – Celotex – was used. This also ensures that there is a consistent U-value over the whole floor area with no cold spots that could attract surface condensation.

Approximate costs (including VAT)

Around 50m² of external insulation, so costs work out at £150/m².

Costs of removing and replacing side passage roof and supports not included.

The ‘specialist labour’ element of this costing is very much a guesstimate as a lot of non-eco-renovation work was carried out by the same people at the same time. If these figures are about right, the costs of internal wall insulation worked out at around £300/m². Retention of period features, and the novelty of the work, contributed to the high cost – which hopefully could be lower in other homes.

How energy use and carbon emissions have changed

As a result of the solid wall and under-floor insulation, gas usage was 20% lower in the first two months of 2010 compared with 2009 (which works out at a 14% reduction in carbon emissions from gas and electricity together, as shown in the graph below). Given that around one third of gas use is for water heating, this suggests the insulation work has resulted in about a 30% saving of heating energy.

Other benefits

Beyond the energy and carbon savings, there have been other important benefits: warmer inside walls have resolved condensation and mould problems; more thermally comfortable space; no slugs! Our home now smells faintly of new wood rather than depressing damp. Lovely.