Oct 03, 2022

Renovating air-gaps

The EU already had aggressive decarbonization targets for its homes before the war in Ukraine. With inflation ravaging due to money printer go brrr, and war leading to shortage of cheap fossils across Europe – I became fascinated by how European homes are actually heated and insulated going forward.

As it turns out: Europe’s homes are reliant on low-quality energy – fossils.
And their insulation is worse than I thought.
The most idiotic yet true answer I found are air-gap-walled homes.

A home with an air-gap wall is simple. Built between ca. 1900 and ca. 1980 across European countries – e.g., Germany, Netherlands and the Nordics – it is a home that has a double outer wall. Think of it like a sandwich where the cheese and ham is just air.

The double wall consists of a thicker interior-outer wall, against which a thinner outer wall, or layer of brick clinker, is built. In between the two walls is air. The air is supposed to function as a natural insulator. Spoiler: its insulation is poor.

It is estimated that up to 27 million homes in Germany are constructed with air-gap walls. An additional 10 million homes across Netherlands and the Nordics. On top of any other European countries I did not research.

While that (lack of) insulation is worrisome in light of current events, what really blew my mind is just HOW reliant these home owners are on fossils. 79% of single family homes and 82% of multi-family homes across the EU+UK heat their homes with gas, oil and coal.

And we pay dearly for it. 34 million households were in energy poverty prior to the Ukraine war. In Germany the expectation is that gas bills for home owners will routinely exceed €3000+.

All this when powering and heating homes is already responsible for more than 20% of CO2 emissions.

As it turns out, we have a proven way to insulate air-gap-walled homes – which are heated 80%+ by fossils – with a retrofit cavity insulation. The technology and approach are proven.

A trained craftsman can tell with 95% certainty just by the age of the home and its construction if it is air-gap-insulated. If it is, insulation foam or granule can be injected into the air-gap easily.

The effect: 50%+ heating cost reduction and a 25%+ CO2 emissions reduction. It costs between €5000 and €10’000 for regular homes.

So it has a fantastic ROI.

However, there are only a couple hundred SMB businesses in Germany doing this retrofit cavity insulation. And many home owners won’t be able to pay it in cash and will need financing.

Time to change that. Who’s working on a tech-enabled insulation business, and can scale up cavity insulations?


EU decarb targets | Energy poverty | Air gap wall | Air gap wall | Cavity insulation approach | Cavity insulation approach | Homes built with air gaps | Estimated number of homes in Germany | Estimated number of homes in Nordics and Netherlands | Example of an SMB doing retrofit cavity insulation | Heating cost reduction potential | Dutch cavity insulation offers | German cavity insulation offers | German web 1.0 player