Reducing our ecological footprint – a personal perspective

Reducing our ecological footprint – a personal perspective

Reducing our ecological footprint – a personal perspective

Dr Rahul Roychoudhuri is an Associate Professor at the University of Cambridge (Department of Pathology) and Theme Lead in Infection and Immunity at the School of the Biological Sciences. From 2015-2020 he was a Wellcome Sir Henry Dale Fellow and group leader in the Immunology Programme at the Babraham Institute.

In this guest blog post, he shares his family’s experience on changes to their 1930's semi-detached house to reduce their ecological footprint, and Rahul also summarises everyday actions his family take to live more sustainably.

Reducing the carbon cost of heating our home

In 2017, my wife and I were shocked to realise that we emit a staggering ~5.5 tonnes of CO2/year to heat our semi-detached 3-bedroom home, despite having a relatively new condensing gas combi boiler for central heating and hot water. This should have come as no surprise: heating is the largest energy-consuming activity in the UK (BEIS, 2017), and our heating-related emissions of 5.5 tonnes of CO2/year were about average for UK households. Over the subsequent years, we have taken the following steps to reduce our carbon emissions through the following approaches:

  1. Insulating our home through actions taken inside and out
  2. Changing our heating and installing an Air-Source Heatpump (ASHP)

In addition to this we are making daily changes to reduce the environmental impact of the way we live and work:

  1. Personal measures: reducing plastic waste and the carbon cost of food
  2. Reducing the carbon cost of travel


1. Insulating our home

Our home is a rather typical UK 1930's semi-detached house, with poorly-insulated external walls (single brick, no cavity). The loft had only a very thin layer of loft insulation. As a consequence, our house always felt cold in the winter. The external walls of the house felt very cold to the touch, and the house occasionally had a damp smell during the winter months.

We addressed the following areas to reduce heat loss:

a) Loft insulation

A quarter of heat is lost through the roof in an uninsulated home, such that, for an average semi-detached house, ~600 kg CO2 / year (and £255) and can be saved by simply insulating the loft. Our first step was to properly insulate the loft - something we did ourselves, along with boarding out the loft for storage and installing a better loft hatch. This DIY project cost ~£200. We replaced the old thin layer of insulation with a thick layer of new fibreglass insulation over the ceiling joists. To board out the loft, we placed loft boards on 175mm loft flooring legs screwed to the ceiling joists to avoid compression of the fibreglass insulation, which would render it inefficient. Since then, we’ve had a loft extension, which is also very well insulated.

b) External wall insulation

The poorly-insulated external walls of the house were built in the 1930s as 'single-skin' (no cavity) walls, cold and damp to the touch during the winter months. To address this, we commissioned a local company to apply external wall insulation (EWI) to the external side and rear walls of the house. The approach involved applying 90mm expanded polystyrene (EPS) external wall insulation to the side and rear walls of the house, and topping with a silicone render. This job cost £7,700 but a £5,000 Green Homes grant scheme voucher covered much of this cost.

Unfortunately, the Green Homes Scheme came to an end in 2021. However, a new government subsidy scheme for home insulation and other energy efficiency measures to replace the Green Homes Scheme is being planned, although a start date has not been specified. The present lack of a subsidy scheme for domestic insulation is a major issue and something I’d urge you to raise by letter to your local MP.

External wall insulation has had a massive impact in terms of reducing our energy usage and on the feeling of warmth in our house. Our hallway beside the side wall of our house always felt cold and damp to the touch during the winter months - this is a non-issue now.

A photo showing internal wall insulation being installed

c) Internal wall insulation

To preserve the front appearance of the house, we did not externally insulate the front wall, but applied internal wall insulation to the front-facing walls of the front rooms of the house (hallway, living room and bedrooms). This was a relatively straightforward and cheap job undertaken by a local handyman, involving battening out the external walls, applying multifoil thermal insulation, fixing plasterboard over the top and then skimming plaster over this. The old trim, picture rails and coving fixtures were simply removed and placed on the new wall.

The internal wall insulation added 5cm of thickness to the wall, so there was no noticeable loss of space to the front rooms of the house, while the rooms are noticeably warmer, more consistently warm throughout and do not have damp/mouldy spots.

Here is a picture of one of the front rooms during the internal wall insulation job.

d) Insulating drafty floorboards

Having drafty floorboards felt like having a small window fully open in the winter - chilly! Like many older houses, our floorboards on the ground floor are suspended on joists above a ventilated space on top of the ground beneath - this needs to be ventilated using air bricks in the wall to prevent condensation and damp to the joists. As a result we had very drafty floorboards, especially when windy, and in the winter, cold air would constantly vent up from beneath the floorboards so it always felt chilly, and we were wasting plenty of energy on heating.

We opted for a cheap and effective way of reducing the draughts between the floorboards by using flexible expansile tubing and applying this between the floorboards. This has made quite a significant difference to the warmth of our ground-floor rooms, and was a very cost-efficient way of improving energy efficiency and warmth in winter.

Important note from Rahul on insulation: Consideration of moisture control is essential to underfloor and other insulation because insulation changes the distribution of temperature, potentially creating new cold spots which condense water held in the air, causing potential damp problems. Therefore, get lots of advice from the web and/or insulation professionals before adding insulation to your home.


2. Changing our heating and installing an Air-Source Heatpump (ASHP)

In 2021, we scrapped our gas combi boiler, and installed an air-source heatpump. Heat pumps are becoming important replacements for gas boilers, and can work with the existing pipework in most water-based central heating systems.

Air-source heat pumps work by absorbing heat from outside (even on cold days) and using the same vapor-compression refrigeration process used by refrigerators to heat the house and hot water supply. The warm water generated by the air-to-water heatpump we purchased is then circulated around either central heating radiators or around a coil inside a hot water tank in the loft to heat water. Air-source heatpumps can switch between heating and hot water and therefore can be used in place of a gas combi boiler.

Importantly, for every 1kW of electrical energy used by an air-source heat pump to pump refrigerant gasses) ~3-6kW of heat is generated (depending on outside temperature and the temperature gradient required). Thus, 1kW of electrical energy input results in 3-6 kW energy output, and much of the heat delivered is 'renewable', having been extracted from the warmth of the outside air. Thus, whereas highly efficient condensing gas combi boilers are ~90% efficient at generating heat from the energy in the gas supplied, heat pumps can be considered 300-500% 'efficient' delivering more heat energy than the amount of energy provided as electricity.

A air-source heatpump installed on a house

Our air-source heat pump was installed on a flat roof above our kitchen extension, and is remarkably quiet. Some of our existing radiators needed to be up-sized and a hot water tank was fitted in the loft. All of this was planned out and costed in a single quote by a specialist renewable heating contractor, and the job took three days to complete. The cost of installation was £12,000, but we were able to recoup £7,700 of this expenditure through the UK government's Renewable Heat Incentive (RHI) scheme - a sum which is now being paid back over a subsequent seven-year period.

Installing a heat pump has dramatically reduced our carbon emissions associated with heating - likely reducing our CO2 emissions to approximately 1.5 tonnes / year, from ~5.5 tonnes / year.

A new scheme introduced by the UK Government called the Boiler Upgrade Scheme (BUS) has recently replaced the RHI and provides an up-front subsidy of £5,000 to assist in the installation costs of a heat pump.

Note from Rahul on running gas-powered condensing combi boilers efficiently: If now is not the time for you to install a heat pump, it’s worth ensuring that you have optimised the efficiency of your existing gas-powered heating system – if you have a condensing boiler, the easiest way of doing so is to turn down your central heating flow temperature to 50-55°C.  Many of us have newer ‘condensing’ gas-powered boilers which provide central heating and hot water on demand. These little units can be remarkably efficient if used correctly. Condensing boilers use waste heat in emitted flue gases to heat cold water either entering the boiler when cold taps are turned on, or the lukewarm water returning to the boiler from the central heating system when the boiler is in central heating mode, using a heat exchanger. Importantly, with condensing boilers, the water vapour that is produced during combustion of natural gas present within the hot flue gasses is condensed into liquid form when cooled down sufficiently in the heat exchanger – releasing further heat from the flue gasses by recovering the latent heat of enthalpy stored in the water vapour. This always happens when a cold-water tap is turned on (i.e. cold water enters the heat exchanger of the boiler allowing water vapour in flue gasses to condense). However, when a condensing boiler is heating the water in the central heating system, the water supplied to the heat exchanger is the water returning from the central heating system, and therefore condensation only happens if the return temperature of the water from the central heating system is sufficiently cold to condense the water vapour. Thus, it’s important to turn down the set flow temperature of the central heating system on condensing boilers to 50-55°C to enable the boiler to enter condensing mode during central heating and thereby to maximise its energy efficiency. This won’t make rooms colder – that’s set by the thermometer which decides how long the boiler is on for. It will simply result in an improvement in the energy efficiency of your gas boiler.  


From cold and drafty to pleasantly warm

As a result of the heat pump and the insulation work to the house, we have benefitted from a much warmer and consistently heated house. Heat pumps operate most efficiently when delivering heat at a constant low temperature - as a consequence, our heat pump is almost continuously, resulting in a house that is ambiently warm. This is a great improvement over gas central heating, with scheduled warm and cool period resulting in rapid warming of air, drying of air with condensation and cold areas of uneven heat. The heat pump kept the house wonderfully warm through our first winter with it - the winter of 2021 - 2022 - with no difficulty whatsoever. Comfort, in addition to carbon emission reduction, has therefore been a major improvement resulting from the installation of the heat pump. There are also potential cost savings as the cost of gas rises due to supply issues resulting from the war in Ukraine.


3. Personal measures: reducing plastic waste and the carbon cost of food

Buying from zero-waste suppliers

We have reduced our plastic waste by buying from zero-waste grocers and household suppliers. We use a local zero-waste household supplier who provide refills on oil and washing detergents, a majority of supplies are in brown paper bags, or in glass/plastic bottles and tubs that are refillable. They deliver, or you can drop by their store in central Cambridge. There are also services that operate throughout the UK who deliver and refill tubs of household goods and food. We also buy our groceries from a local zero-waste supplier and have milk delivered (in glass bottles).

Do It Yourself

We make bread at home using a breadmaker, saving all the plastic bags used to package bread. We also routinely make yoghurt (from our delivered milk) and humous (from dried chickpeas) using a pressure cooker - creating a further plastic saving.

Going vegetarian

We were already vegetarian, however, reducing meat or going veggie is an excellent way of reducing the extensive carbon cost associated with meat production.

Buying in-season local produce

Avoiding flying green beans half way across the world was a no-brainer for us. We've really enjoyed the seasonality of our cooking that has resulted from buying local produce, and have broadened our palate.


4. Reducing the carbon cost of travel

Biking about - with or without passengers!

We chose to work and live within cycling distance, making our commute fun, and good exercise. We never get stuck in traffic!

Depending on your budget and the number of children you will be regularly transporting, a bike child seat or cargo bike is an excellent way to transport kids to and from school, and saves on all those car journeys.  We have a cargo bike which has been a fun and efficient way to get kids to and from nursery and school. There are a lot of options for families who need to cart kids around to school, activities and errands.

Reducing international travel

We have been:

1. Trying to go on holiday locally as much as possible, or in nearby European countries

2. Reducing international travel for work (for example, I have chosen to attend conferences which are nationally held, or held in nearby European countries)

3. Making use of Zoom, Google docs and other internet-based tools for collaborating remotely. This has also been a game-changer for work productivity in addition to reducing carbon costs associated with work travel.


Thanks to Rahul for sharing this article on his approach. Some other members of our community have described their experiences of greening their homes or buying their first electric vehicle so take a look at the links below if you'd like to learn more. The Green Labs initiative at the Institute is working across the Institute and Babraham Research Campus to reduce the ecological footprint of our research and related activities and also to raise awareness of environmental issues and inspire change.