Milton Keynes Council - Lakes Estate regeneration phase 2 monitoring

Milton Keynes Council wanted to develop a greater understanding of the energy performance of their retrofitted homes, so we were appointed to undertake a research study to determine energy and carbon savings, resulting from a set of retrofit energy measures that had been installed.

The Milton Keynes Council phase 2 planned development retrofit programme included the installation of energy-saving measures across 381 properties. We undertook a pre and post-retrofit monitoring study on a sample of eight representative properties, which included the upgrade of:

  • Cladding.
  • Flat roofing.
  • Roof lights.
  • Loft insulation.
  • Boilers and heating systems.
  • uPVC windows.
  • uPVC external doors.
  • Additional ‘minor’ works including asbestos removal and sealing air leakages/draughts.

Services and key activities we provided

The project aimed to provide a business case justification for retrofit, and address quality and comfort concerns around retrofit.

To achieve this we:

  • Measured energy consumption (electricity and gas) and environmental parameters (internal and external temperatures, internal relative humidity levels and carbon dioxide concentrations) both before and after the refurbishment works.
  • Tested building fabric performance (wall and roof U-values, and air permeability) pre and post-retrofit.
  • Conducted a Standard Assessment Procedure (SAP) evaluation based on ‘as measured’ and SAP default values.
  • Undertook a ‘before and after’ Building Occupancy Survey to better understand how tenants typically used energy within the houses.

Lakes Estate SAP improvement graph

Our findings

  • SAP energy efficiency rating improved by 19% and the environmental impact by 25% (on average).
  • Average (excluding B1) gas usage reduced by 24%.
  • Average total energy (excluding B1) reduced by 15%.
  • Post-retrofit electricity was between the average and lower than minimum NEED figures.
  • Post-retrofit gas was between the average and lower than minimum NEED figures.
  • Infra-red thermal imaging confirmed that previously installed blown mineral wool was not 100% complete and was only partially successful in reducing heat loss through external walls.
  • Air permeability was found to be better than the current building regulations in six out of eight properties pre-retrofit, and in all properties post-retrofit.
  • Seven properties performed well with regard to internal air quality, as determined by the measurement of carbon dioxide (CO2) concentrations. The exception was a single-storey bungalow (B2) which showed higher CO2 concentrations than ‘typical’.
  • The average ‘as measured’ external wall U-value (from an in-situ U-value test) was found to be worse than the average ‘as calculated’ value (from SAP methodology construction wall types) and provided supporting evidence that cavity wall insulation was not 100% complete.
  • The ‘as measured’ roof average U-value was found to be significantly lower (better) than the ‘as calculated’ and demonstrated that the material used and the works associated with the flat roof replacement were of a high standard.
  • Two properties had significant overheating in their bedrooms post-retrofit, but insufficient data was available for comparison with pre-retrofit conditions.
  • There were no significant changes in relative humidity between pre and post-retrofit.
  • All tenants reported that they felt warmer post-retrofit, and believed they paid less for their energy. 

 

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