Our Work

47 Greenleaf Road Retrofit Home

Homes are the biggest carbon emissions contributor, so retrofitting a traditional Victorian terrace shows residents the changes they can make to their homes to save energy, money and reduce their carbon footprint.

47 Greenleaf retrofit

Waltham Forest Borough Council appointed long-standing partners Aston Group to manage the retrofit of a council owned property, into its first-ever eco show home. 47 Greenleaf Road as a typical Victorian terrace built in 1902 with a poor energy performance.

A report published by Waltham Forest Council
in 2019 highlighted that 51% of the borough’s carbon emissions were generated by residential homes. The same report also revealed that 14.6% of homes in the area were fuel poor households. New-build properties with energy-efficient technology are only part of the solution.

With 70% of Waltham Forest’s 107,216 homes pre-dating 1944, it’s vital to find a way to reduce carbon emissions from existing homes, through retrofitting. The annual heat demand from this home is estimated to fall from 17,219kWh to 7,995kWh per year, while the EPC banding will rise to from E to A.

Working with Aston Group the London Borough of Waltham Forest set the challenge of raising the property’s EPC rating from band E to band A, while reducing its carbon usage by approximately 50 tonnes of CO2 over 30 years, using a wide range of measures throughout the property, from improved thermal insulation, heating and ventilation, to the introduction of solar PV and battery storage.

Greenleaf Road Retrofit Case Study Film

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Back of the property


Comparisons and analysis have been undertaken in order to compare the thermal performances between the original building and the design performance (calculated using the government approved SAP methodology). A regime of testing was also undertaken in order to validate the improvements.

Having set clear goals at the outset of the retrofit project, it was important to demonstrate the effectiveness of the measures implemented at 47 Greenleaf Road. Here are some of the top line results.

Improved energy use
improved running costs
reduction in CO₂ emissions

Thermal upgrades

Wall insulation

External wall insulation (EWI) was installed to the side and rear elevations of the property, using a 90mm EPS slab with a top-coat of render. EWI was not feasible on the street elevation in order to avoid loss of character to the property, therefore, Internal wall insulation (IWI) was installed to this façade using a 57.5mm insulated plasterboard.

Roof insulation

The roof was upgraded to 300mm of mineral wool insulation (between and above joists). This as expected to reduce heat loss through the roof by 50%.

Underfloor insulation

Floor insulation was installed to the main suspended floor via the Q-bot insulation system. Details can be found in the separate Q-bot impact report, however, was expected to reduce heat loss through the floor by up to 74%.


New high-performance double glazing was installed into the existing window frames.

Service upgrades

Mechanical ventilation

In order to further reduce heat loss and improve internal indoor air quality, a mechanical ventilation system with heat recovery was installed to provide fresh air throughout the dwelling.

Heating system replacement

The existing gas boiler has been replaced with an air-source heat pump, and associated hot water cylinder. This was predicted have a dramatic impact on the buildings carbon emissions, especially as the carbon intensity of the national grid is decreased with the uptake of renewable generation.

Photovoltaic array

A 3.9 kWp solar photovoltaic array has been installed, with associated battery storage. This should be capable of producing approximately 2,850 kWh of electricity per year, and the battery storage system shall maximise the amount of this energy that can be used by the occupant. Click here to see the results.

Waste water heat recovery system

A heat recovery system has been fitted beneath the bath, in order to recover a percentage of the heat lost down the drain, and recover this to the hot water system.

The original building reported an EPC E, after works the building has now achieved an EPC A.

Carbon savings a year
Air source heat pump and radiators 4,240kg
Solar and battery PV 853kg
Underfloor insulation 287kg
Solid wall insulation 890kg
Loft insulation 580kg
Cost savings a year
Air source heat pump and radiators £860
Solar and battery PV £609
Underfloor insulation £67
Solid wall insulation £341
Loft insulation £120
How is the solar PV performing?

The system installed at 47 Greenleaf is a 10Kwh battery system. The below and attached (“Battery evaluation for 47 Greenleaf Road”) shows the added benefit of installing a 10 kWh battery as opposed to a 5kWh and PV only.

The Grid independence (how much in % the property does not rely on drawing from the Grid) is far greater than if Solar PV only was installed. In summary, 23.57% with only Solar installed and 70.71% grid independence with a 10kWh battery. This would drop drown to 59.4% with a 5kWh battery so it was beneficial having the 10kWh battery.

Self-consumption with electrical energy storage device %63%75%
Self-consumption with electrical energy storage device, kWh20792475
Grid electricity independence without electrical energy storage device, %23.57%23.57%
Grid electricity independence with electrical energy storage device, %59.40%70.71%
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Installing the air source heat pump


With thanks to our partners, Stroma, Status Design, Q‑bot, Saving Energy and Spartek

We are fortunate to live in a borough populated by passionate, engaged and conscientious people and partners like Aston Group who have proved time and again that they care about helping Waltham Forest to be the best it can be. This eco home is London’s first Council owned retrofit property and is testament to how serious we, and Aston Group are in tackling the climate emergency. Housing is the largest contributor to carbon emissions in Waltham Forest so it’s vital we show leadership, as well as signpost and demonstrate the viable options and technologies to our residents so that they can see what they can do to reduce the carbon footprint of their home and improve their behaviours. This collaboration with Aston Group means that local people can see what they can do to reduce their carbon footprint and do so with a high level of trust.”

Cllr Clyde Loakes, Deputy Leader and Member for Environment and Cllr Louise Mitchell, Member for Housing and Homelessness