Cambridge City Council: Bridging the gap to net zero

Tackling climate change and making Cambridge cleaner and greener has been one of Cambridge City Council’s key priorities for the past 15 years. The council has delivered a wide range of projects and activities to reduce carbon emissions and adapt to climate change in Cambridge and has reduced its own emissions by over 28 per cent through the implementation of its Carbon Management Plans.

Cambridge City Council declared a Climate Emergency in February 2019 and in its new Climate Change Strategy 2021-2026 set a target to reduce the council’s direct carbon emissions (from its corporate buildings, vehicles and business travel) to net zero by 2030 and shared a vision for Cambridge to be net zero carbon by 2030.

The challenge

In line with these ambitions Cambridge City Council has started reviewing its own council housing stock and what it can do to these properties to reach net zero. The council already has a programme of installing External Wall Insulation (EWI) but wanted to explore the extent of the gap to reaching net zero carbon, so the council embarked on a whole house retrofit of a property undergoing EWI.

The solution

The planned works programme delivers 90mm of EPS solid wall insulation with a render finish. As scaffolding was already being put up it was decided that installing Solar PV would add minimal expenditure but offer our tenants greater benefits and further increase our Energy Performance Certificate (EPC) rating. On the retrofit house a 2.24kW Solar PV system was installed.

To go a step further and with the opportunity of the property being void we wanted to explore different underfloor insulation options. Q-Bot was chosen as the property has a suspended floor and we wanted to establish if it was suitable for properties with residents in situ. Q-bot uses a robot to spray the underside of the floor with insulation, this innovative method of installation avoids lifting all ground floor floorboards. As the windows weren’t due to be replaced, we decided to trial a low-cost draft poofing system called Quattro seal to improve the air tightness. Quattro Seal is a robust liquid sealing system that deforms to any shape and style of window irrespective of fabric or size.

We also Installed a Switchee smart thermostat, Endotherm central heating additive and replaced the old single glazed leaky doors on the property. Throughout the programme of works we carried out airtightness tests including trailing pulse equipment air testing - an alternative method of air tightness testing to the traditional blower door method. The Retrofit house project as a whole cost in the region of £25,000 to deliver with additional staff time involved with procurement and contract management.

The impact

The Property was modelled in SAP before and after and air testing was conducted in between installation of different measures. The results were as follows:

  Before installation After completion
EPC rating D 67 B 88
Environmental impact 3.5 tonnes of CO2 1.7 tonnes of CO2
Estimate Annual Energy Costs (EPC) £817.00 £561.00
Estimated Primary Energy Usage 221 kWh per m2 73 kWh per m2


Lessons learned

As with any external project, the weather was a major challenge especially with such unseasonable weather into spring when the project started. This cold weather meant that we could not render the properties until conditions improved and was also hindered by the rain. Other issues we were faced with on the wider project included extensions and outbuildings meaning scaffolding could not be erected and these needing to be removed and reinstated. We also experienced some technical issues with the underfloor insulation which led to additional floor boards being taken up which was practical in a Void property with wood flooring but may not be practical in an occupied property with carpet and furniture.


Juliet Nicholas, [email protected]