Retrofit for the future: Nelson Street, Oxford


This retrofit project in Oxford targeted reductions in energy consumption of 85% by using an optimum mix of energy demand-reduction measures and well-proven zero-carbon technologies.


The case study house is a typical 19th century, solid brick walled, slate roofed two-bedroom semi-detached house which has had some refurbishment in recent years (area: 76.9m2). The house front has a south-east solar orientation. The two extensions to the property had unfilled cavity walls, concrete ground floor and a flat roof. The building is of a decent homes standard and is located in Jericho, adjacent to an area where there is a strong Victorian vernacular of historic value. The house is representative of the numerous other similar properties in Oxford. The proposals are replicable to different types, eras and orientations of low rise housing.


The 'low-energy first and then low-carbon’ approach has been informed by a thorough, pre-retrofit monitoring and feedback survey during Phase 1. Monitoring of internal temperatures showed that average temperature in rooms was maintained at 16 deg C and hence, the annual fuel bills were almost half of what SAP predicted. The occupants complained about a 'cold' house which is difficult to heat due to lack of insulation and rising fuel costs. Also, 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 are applied to achieve a robust and practical whole-house retrofit solution:

  1. FABRIC IMPROVEMENT: INSULATION: Building fabric is improved to stringent U-values, high-performance triple-glazed passivhaus windows and composite insulated external doors.
  2. MINIMISATION OF THERMAL BRIDGES: using 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. DAYLIGHTING: Roof-lights added, as monitoring showed daylight factors of <1% in north-facing spaces.
  3. AIRTIGHTNESS: air permeability of 1m3/hm2 @ 50 Pa is targeted. Upgradation of windows and doors, minimising thermal bridges and insulating and sealing all air leakage pathways to achieve an airtight fabric.
  4. VENTILATION: Mechanical ventilation system with heat recovery (MVHR) is installed to provide controlled ventilation and maintain an an appropriate air change rate.
  5. EFFICIENT SYSTEMS: LED lighting throughout, along with available A++ energy rated appliances, automatic standby savers, voltage optimisation and A-rated gas condensing boiler.
  6. ZERO-CARBON TECHNOLOGIES: A 3m2 evacuated tube solar thermal system with a low-energy pump, and a 1kWp photovoltaic system.
  7. EXTRA MEASURES: Water conservation measures, low solvent paints etc. A bespoke monitoring and feedback system will display real-time gas and electricity use, internal temperature, humidity, CO2 levels, and any energy being wasted through open windows, unused equipment and lighting.


YEAR 1 Post refurbishment GAS : 68% reduction over pre-refurbishment actual

YEAR 1 Post refurbishment ELECTRICITY: 23.3% reduction over pre-refurbishment actual

YEAR 1 Total energy consumption (kWh/ year): 58.6% reduction over pre-refurbishment actual



Research Reports

  • Gupta, R. (2006) Applying CO2 reduction strategies to existing UK dwellings using GIS-based modelling: a case study in Oxford. Findings in Built and Rural Environment (FiBRE). RICS journal
  • Post-retrofit completion and monitoring reports (Quarterly)


Blogs & Diaries

  • Retrofit for future diaries
    Dated: July 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.


Low Carbon Building Group

Oxford Brookes University
Headington Campus
Gipsy Lane
Oxford, OX3 0BP