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Low Energy Refurbishment for a Post-War House.

Updated: Jul 19, 2022

In 2019 our clients bought a detached post-war house in Coombe Dingle, a leafy suburb in North-West Bristol, sandwiched between the parkland area of Blaise Castle Estate and the Trym valley. The aim of the project was to balance a substantial increase in floor area with the desire to retain and reuse the bulk of the existing building fabric.

New Front Elevation

The area comprises large, detached arts and crafts properties set in generous plots interspersed with smaller, post-war infill developments and a handful of contemporary dwellings. The clients wanted to turn the existing, standard 3-bed house into a low-energy, 4-bed home with a generous, open plan kitchen / dining / living area and separate cinema room, hobby room and utility / plant rooms.

Existing Plans

We initially produced several redevelopment options exploring different strategies: full width double-storey rear extension, front extension, part single and part double-storey rear extensions. The final scheme comprises a large part-single, part double rear extension and a remodelled street elevation including the removal of an unsightly front extension. Due to the objections of the adjacent neighbour, the planners required a small reduction in size of the double-storey element.

After planning consent was granted, we set out a strategy to upgrade the building fabric of the existing property to ensure minimal heating demands.

The existing, uninsulated cavity walls have been overclad with 120mm expanded polystyrene insulation with a flexible render system (the U-value of the walls rose from 0.6 approximately to 0.2 W/m2K). The external walls' plaster extends to the floor slab (unlike standard construction) and all wall / floor / ceiling junctions are sealed and taped to provide an airtight construction.

Mechanical ventilation with heat recovery (MVHR) is provided throughout the house, delivering fresh pre-heated air to the habitable rooms and extracting stale, wet air from the kitchen and bathrooms. MVHR installation is only recommended when the building's airtightness is less than 4 air changes per hour; a preliminary air pressure test carried out after the first fix produced a very reasonable result of 3.1 air changes per hour so the system was deemed worthwhile.


All windows have been replaced with efficient, triple glazed alu-clad timber windows which don't have leaky trickle vents because the MVHR provides sufficient background ventilation. Due to the careful planning of the MVHR, most ducts run within existing cupboards or service areas and only in one room a bulkhead has been introduced.

A large photovoltaic array on the south-facing roof pitch provides approximately 60% of the household's electrical requirements, resulting in a considerably saving on energy bills. Any surplus electricity is diverted to the heating coil of the hot water tank. The solar panels also feed into the electrical car charging point which means most car journeys are effectively free! Smart thermostatic radiator valves provide individual, room-by-room heating control in conjunction with a thermostat kit; they can also be managed through a smartphone app.

Rear elevation with triple glazed alu-clad timber windows

The refurbished property is now a spacious, comfortable low energy family home of contemporary design whose gas and electricity consumption has been reduced approximately by 40%, despite a 42sqm increase in floor area (from 174 to 216sqm).

Front & rear elevations before and after

DHVA combine award-winning contemporary design ability and attention to detail to help our clients create beautiful spaces tailored to their needs. Contact us for a no obligation discussion about your project on 0117 914 8317 or email

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