For the most part, houses built before the turn of the 20th century did not have bathrooms. Ablutions required a cold and dark trip to an outhouse, often perched over a pit in the ground. Yet within a few decades, the modern bathroom evolved from a novelty into an almost-universal residential fixture. Thomas Crapper’s valve-and-siphon design was patented in 1891, and found its way into British homes all over the country in the decades preceding World War I.

This story of the plumbing revolution illuminates how I think we should address the retrofit challenge. Today’s opportunity is to use active building technology to make the next leap forward in domestic health and wellbeing.

It is well known that emissions need to be addressed. It is less well known that of the 30,000 typical excess winter deaths in the UK, between 30% and 50% are due to cold homes. Conversely, homes also get unpleasantly hot in summer – with indoor air quality often excessively humid, low in oxygen and polluted.

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