Retrofit for the Future - Nelson Street, Oxford

Principal Investigator(s): Professor Rajat Gupta


Project start: January 2009

Project finish: December 2013

Funded by: Innovate UK

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This retrofit project aimed to reduce energy consumption at a residential property in Oxford by 85% by using a mix of energy demand-reduction measures and well-proven, zero-carbon technologies.

The case study house was a typical 19th century, solid brick walled, slate roofed, two-bedroom semi-detached house which had had some refurbishment in recent years (area: 76.9m2). The house front was a south-east solar orientation. The two extensions to the property had unfilled cavity walls, concrete ground floor and a flat roof.

The building was of a decent standard and was located in Jericho, adjacent to an area where there is a strong Victorian vernacular of historic value. The house was representative of the numerous other similar properties in Oxford. The proposals were replicable to different types, eras and orientations of low rise housing.

Case study house with thermal imaging

Research impact

Front door with and without thermal imaging

One year after the refurbishment, the following benefits were observed:

  • Gas: 68% reduction over pre-refurbishment actual
  • Electricity: 23.3% reduction over pre-refurbishment actual
  • Total energy consumption (kWh/ year): 58.6% reduction over pre-refurbishment actual


Rajat Gupta

Professor Rajat Gupta

Professor of Sustainable Architecture and Climate Change, Director of OISD and LCB Group

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The 'low-energy first and then low-carbon’ approach was informed by a thorough, pre-retrofit monitoring and feedback survey during Phase 1.

Monitoring of internal temperatures showed that average temperature in rooms were maintained at 16 degrees Celsius and hence, the annual fuel bills were almost half of what Standard Assessment Procedure (SAP) predicted. The occupants complained about a 'cold' house which was difficult to heat due to lack of insulation and rising fuel costs.

Internal air quality (CO2 levels) and daylight levels were found to be poor. Thermal imaging confirmed the fabric heat losses.

In line with this, a range of measures were applied to achieve a robust and practical whole-house retrofit solution:

  • Fabric improvement - insulation: Building fabric was improved to stringent U-values, high-performance, triple-glazed passivhaus windows and composite insulated external doors.
  • Minimisation of thermal bridges: Used accredited construction details, by detailing for continuous insulation and air barrier on external walls to prevent condensation, party wall insulation and using a thermal laminate on the underside of the roof in the ceilings of the bedrooms.
  • Day lighting: Roof-lights were added, as monitoring showed daylight factors of <1% in north-facing spaces.
  • Airtightness: Air permeability of 1m3/hm2 @ 50 Pa was targeted. Upgradation of windows and doors, minimising thermal bridges and insulating and sealing all air leakage pathways to achieve an airtight fabric.
  • Ventilation: Mechanical ventilation system with heat recovery (MVHR) was installed to provide controlled ventilation and maintain an appropriate air change rate.
  • Efficient systems: LED lighting throughout, along with available A++ energy rated appliances, automatic standby savers, voltage optimisation and A-rated gas condensing boiler.
  • Zero-carbon technologies: A 3m2 evacuated tube solar thermal system with a low-energy pump, and a 1kWp photovoltaic system.
  • Extra measures: Water conservation measures, low solvent paints, etc. A bespoke monitoring and feedback system displays real-time gas and electricity use, internal temperature, humidity, CO2 levels, and any energy being wasted through open windows, unused equipment and lighting.


Refereed journal articles:

Blogs and diaries

  • Retrofit for future diaries, July 2011


  • Oxford Whole House Carbon Reduction Project, March 2011

Conference keynote

  • Gupta, R. (2010). Building performance evaluation for low-carbon refurbishment of a Victorian house in Oxford. Keynote. Retrofit for the future. Constructing Excellence Oxford. 27 January 2010, Said Business School, University of Oxford, Oxford.