Refurbishment of Listed Grade II House, Cotham, Bristol, England.
Low energy, sustainable conversion of house.

Green Star Award 2011
Redland & Cotham Amenities Society

A private 247m2 semi-detached 4 storey house (plus cellar) with small rear garden. The house was built in 1860's in random rubble, the front finished with ashlar stone and the side/rear with render. Floors and roof are of timber construction. A plaster cornice and the original internal joinery is only found on the upper ground floor (entrance) level. In a conservation area the house was listed of historical interest Grade II in 1997.

Typical of properties of this age the thermal performance was very poor. Despite Bristol City Council's claim to support the making of properties more sustainable, planning permission was refused to overclad the existing rendered side and rear with an insulation/render system and put solar panels on the side roof. On appeal the council's opposition to the external insulation was overturned.

The conservation area location and listing of this house has inhibited the upgrading. English Heritage's guide to work on such properties is very conservative and biased. Building science is often poorly understood or risks to fabric misrepresent, these severely limit options for upgrading and what is considered allowable unless challenged. There is no doubt the thresholds of what now should be acceptable need to change in the context of climate change, and need to conserve energy.

The technologies that are now common in low energy houses are also represented in this house:-

• 4.5sq m flat plate solar thermal panels with two 150ltr. hot water storage cylinders
• 2.4kWp solar photovoltaic panels
• heat recovery ventilation installation controlling moisture, and recovering energy from exhausted air
• low E double glazing in new timber sash windows to match existing all weather stripped
• restoration of window shutters on all dayspace windows (when closed better performance than triple glazing)
• a high efficiency wood burning stove
• complete upgrade of the thermal performance of the building fabric, with new insulation of floor, walls and roof
• low energy white goods and extensive use of LED GU10 lamps
• 3 zones for space heating with individual time control.

The external fabric is now well insulated. The external walls are overclad with 80mm thickness of phenolic insulation with a cementitious polymer-modified render finish. The worst case U values are for the roof 0.25W/m2K, walls 0.20W/m2K, floor 0.15W/m2K. The roof has the apex void fully filled with mineral wool and flanking attic spaces are fully insulated and separated from the house by insulated floors.

Useful thermal mass is provided by the inclusion of 500mm+ thick external stone walls within the insulation layer. The internal stone and brick walls also contribute to thermal mass which helps even out temperature variations and reduces energy consumption.

Many of the features outlined in the 'Code for Sustainable Homes' and 'Lifetime Homes Standards' are included:- bike store, composting of waste, home working, internal & external drying space, energy display devices, renewal technologies (LED's), rain water storage, natural ventilation and lighting, adaptability & car parking access.

The upgrading of the Cotham house has resulted in a 50% reduction in energy usage to the equivalent of 70kWh/m2/y. This is better than the PassivHaus max. of 120kWh/m2/y (although the comparison is not strictly like for like, the Cotham house is 247m2 with high ceilings 3100-3500mm floor/floor dims., a PassivHaus is usually 120m2 with 2700mm floor/floor dims.). The embodied carbon in the construction of the Cotham house is very low (local stone, lime etc. constructed with man and horse power, some timber from the Baltic brought by sailing boat). A code level 6 120m2 house would have an annual energy usage of 50-66kWh/m2/y.

all coloured areas have been upgraded - the plaster cornice, shutter boxes & joinery in the principle front room prevent work to the front ashlar faced front wall

hammer fixing 80mm KEW5
phenolic insulation


1st coat mesh reinforced polymer
modified cementitious mortar

distortion in toughed double glazed
low E glazing units in new timber sashes
(fully weather stipped)

Solar PV installation on side roof not permitted - planners said would harm listed building and conservation area (appealed against decision was unsuccessful)

2.4kWp photovotaic located in alternative position at bottom of garden output compromised by overshadowing by neighbour's tree & house (annual loss in output 20% - what cost conservation?)

PV's mounted on open-sided timber pergola

neighbour's & house solar thermal panels output compromised by discreet location - frost on both evacuated tube & flat panel types (note output similar of these types) - annual loss less than 5%

concrete raft under-pinning of front of house