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:
- 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.
- 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.