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Whole house energy retrofit at end-of-terrace home in the South Wales Valleys

Whole house energy retrofit

Wales & West Housing have worked with us on the Low Carbon Built Environment project (LCBE) retrofitting a typical solid wall east-facing end-terrace home in south Wales.

A combination of low-carbon solutions has been installed to reduce energy demand, provide renewable energy and store energy at the home. Also, an efficient gas boiler provided both space heating and hot water, with a shower that was powered by electricity. The family living at the property were at home most of the time.

The existing building conditions and how the home was likely to be used were considered during the planning and design of the whole house retrofit. This approach ensured that appropriate combinations of low-carbon technologies were selected. A comprehensive programme of modelling and monitoring was carried out before and after the work was undertaken.

Low carbon solutions

The low-carbon solutions we used were:

  • reduce energy demand by installing internal wall insulation (front elevation), external wall insulation (gable and rear walls) and loft insulation, plus mechanical ventilation with heat recovery (MVHR)
  • renewable energy supply through east- and west-facing building integrated photovoltaic (BIPV) solar panels, plus a Transpired Solar Collector (TSC) on the gable wall
  • energy storage using a Tesla Powerwall 2 battery that is optimised for self-sufficiency and supported by various electrical works


Once the work was complete the residents confirmed that the home felt more comfortable. The average temperature in the living spaces increased and was more consistent.

The ventilation system supplied clean, warm air to the living spaces, and removed damp air from the bathroom and kitchen. The average relative humidity decreased, reducing the risk of condensation and mould growth.

The home’s Energy Performance Certificate rating improved from E (47) to B (89) after the retrofit.

The insulation improvements reduced the need for heating, with the family using 30% less gas. Over the same period, the electricity generated by the solar panels meant that the amount of electricity that the family had to import from the grid was reduced by 76%. In the spring and summer, more electricity was produced by the solar photovoltaic (PV) panels than was consumed in the home, with the excess being exported back to the grid.

Lessons learnt

Installing solar PV panels on both the east and west-facing roofs meant that energy could be generated throughout the day. Many homes in the South Wales valleys are located on either side of south-to-north running valleys making installing panels on both roofs an option. This home demonstrates that this works very well.

The transpired solar collector creates warm air which enters the ventilation system and reduces the energy needed to heat the home.

The ventilation system improves air quality and reduces humidity. Lower air humidity reduces the risk of condensation and mould growth. Residents reported respiratory health improvements.

Having a construction manager who oversees the project working alongside a skilled and flexible supply chain improves the efficiency of the installations. They can also act as a single point of contact to ensure residents stay happy.

The retrofit was carefully planned and designed to coincide with fairer weather conditions. However, supply chain delays meant that the work was pushed into the winter months. The installers then had to attempt to reschedule their tasks to fit into the revised work plan. This was not always possible, which led to further delays and tension with the residents. This situation required clear and consistent communication with residents to ensure that they remain positive.

Project team

The project team includes:

  • the Low Carbon Built Environment team at the Welsh School of Architecture, Cardiff University
  • Wales & West Housing
  • contractors and suppliers who supplied and installed each low-carbon technology