Building Performance Evaluation Programme: Findings from domestic report

Key Findings

  • Nearly ten times as much energy was used in the highest energy-consuming home as the lowest. The average grid electricity use across the buildings was 42 kWh/m2, while the mean for fuel and biomass was 71 kWh/m2.
  • Average total carbon emissions were 2.6 times higher than the average design estimate. None of the ‘zero-carbon’ design estimates were achieved in practice.
  • Every project had better air tightness than the minimum requirement of building regulations. Tests found average air tightness of 4.6 m3/h/m2@50Pa – far better than the 10 m3 required by building regulations.
  • Homes built to passive house standards achieved the best air tightness and insulation values, which meant they had the lowest heat loss and best thermal performance.

Further Detail

Passive house design focuses on insulation and air tightness more than other construction techniques. They achieve the best heat-loss coefficients and thermal performance. Heat loss coefficients are only as good as the weakest link within the thermal envelope, which are usually windows.

During early adoption of new technologies, teething problems are inevitable and compromise carbon performance in most cases. Among these technologies are solar water heaters, heat-recovery ventilation, automatic blinds and heating controls. Designers must be wary of using innovative systems unless they know the installers have used them before in similar contexts.

Automatic blinds were used within the design of a handful of the studies presented. Innovate suggest: ‘…avoid(ing) automatic controls for systems like window blinds, because most are set up to lower in sunny weather. This denies residents solar gains through windows in the winter, which can be important heat source, especially in homes built to Passive House standards.’

Summer temperatures in 67 of the homes were recorded. Every home’s peak temperature was above 25°C which above the comfort threshold, however in some homes this was just for a short period of time and only occurred in the daytime. Just under half of the properties, had temperatures above 28°C but these hot periods were very short at less than 0.6% of the time on average over summer (May to August).

Homes with external shading – including movable blinds – were less likely to become uncomfortably hot (above 28°C) in summer. Although better insulation and air tightness may increase summer temperature, evidence suggests that window opening routines and external shading can help overcome this.

To read the report in full, click here.

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