Climate Friendly Retrofit Part 7: Halving our Heating Demand

Josiah Lockhart
4 min readSep 10, 2021


Yesterday, my friends over at Nesta Scotland released an initial study on what it would take to decarbonise heat in Scottish Homes. Of many areas this report covered, the resounding sentiment throughout was that all the technology was dependant on the fabric of the building. It’s often exciting to jump to talking about solar panels, heat pumps, and cutting-edge technology, but if you are embarking on a retrofit of your own, the biggest impact for your money will always be in improving the fabric of your building. By that, I mean insulation, windows, and draught-proofing. Without addressing these at the start of any project, all the technology must work harder and is often unsuitable.

Cold February in Lockdown

When we purchased the property for our retrofit, it had an EPC of E, and was partly single glazed (including a single-ply plastic skylight), open fireplaces, and an assumed lack of insulation throughout. Our EPC report recommended roof insulation, room in roof insulation, cavity wall insulation, underfloor insulation, and window upgrades. And having moved in at the end of January, it felt like this was correct. The house was so cold (partly from being left vacant for a few years) we had to run the heat constantly for nearly a week to simply get the house up to a comfortable temperature.

EPC of 49
Original EPC

Our plan, when we assumed there was nearly no insulation, was to work to a passive house standard with Icynene insulation throughout. Not long after we were in the house, we commissioned an “invasive” survey which discovered that there was a random mix of 1990’s standard insulation throughout most parts of the house (including 3 different types of wall insulation, 4 different types of roof insulation) with the only missing insulation being under the floor. While this was better than we thought, it posed a dilemma for our insulation plans as meeting passive house standards would now require us to remove old insulation before replacing it. Having done the maths, the payback from this would take 70–80 years, and we decided to simply adapt our plans and only insulate places where there was no insulation, this did, however, increase our end of project heating demand (at least on paper).

What the survey did show was most of the heat loss was from several poorly installed windows and our open fireplaces. So once lockdown eased, we set on task for replacing the single glazed windows and skylight with high-performance triple-glazed, fixing all the badly installed windows, installing a high-efficiency wood stove in the open fire and insulate the floor and plumbing. Work that costs us £5.3k altogether. Now that the fabric has been dealt with and our solar is installed, we have just had a new Energy Performance Certificate carried out on the property going from a 49 E to a 92 A with our predicted space heating demand more than halving from 43,541 kWh per year 20,772 kWh.

Had we token to installing a new heating system first, we would have wasted loads of time, energy, and money on a system that needed to work twice as hard as it does now. Hopefully, this drives home the point in how spending money on improving the fabric of the house pays off in the long run. My only recommendation for policymakers is they need to better incentivise this part of the process for homeowners, if I had to insulate from scratch, it would have cost £16k of which there is only a loan of £5k available (and grant of £2k) through Home Energy Scotland, and even then it is limited to certain types of insulation. There is still some way to go before making this accessible to the UK population.