The material for your house is under your feet every day.

Every spring in Djenné, Mali, an entire town climbs onto a mosque. The mud is mixed for weeks beforehand. On the day of the festival, children carry it up in buckets and the masons spread it over the walls with their palms. By evening, the largest mud building in the world has a brand-new skin. No crane, no cement, no invoice.

You, for a two-bedroom flat, need a thirty-year mortgage. Your grandad wasn't richer than you. Nobody had just told him it couldn't be done.

The idea

The claim: the cheapest, most durable building material in history wasn't pushed aside because it failed. It was pushed aside because nobody makes money from it. And it never left the ground under your feet.

Mudbrick, or adobe, is mud, sand and straw. You press it into a wooden mould, turn it out and leave it in the sun for two or three weeks. No kiln, no factory, no lorry. The only fuel is the sun and your own hands. The material is already on the plot.

It isn't a poor man's solution that got left behind. Jericho, one of the oldest permanent settlements ever excavated, was being built in mudbrick more than ten thousand years ago. Taos Pueblo in New Mexico has been lived in for about a thousand years. In Shibam, Yemen, around five hundred mud towers still stand, many of them more than five storeys high, most dating from the 16th century. They call it "the Manhattan of the desert". In Thessaly, in Greece, mudbrick houses were the norm in many villages, and plenty are still standing. There were skyscrapers made of mud before there was steel.

The secret is thermal mass: the ability of a heavy wall to store heat. A thick earth wall soaks up the midday heat and lets it through to the inside almost half a day later, at night, when it's cold outside. In the morning it does the reverse. Anyone who's walked into an old stone or mudbrick house in summer knows it: an oven outside, cool inside. No air conditioning, just physics.

And the wall breathes. Clay draws moisture out of the air and releases it again, instead of trapping it. Researchers at Berkeley Lab, a US Department of Energy laboratory, estimated that nearly half of American homes have damp or mould. Whether earth walls would spare them all, nobody has measured. That clay regulates humidity has been measured many times.

So why doesn't anyone build like this? The United States shows it clearly, because there the change happened within a century and left a paper trail. First came the railway, bringing cheap timber. In 1927 the first uniform building code appeared, written for wood and concrete. Mudbrick wasn't banned. It just wasn't provided for. And anything not provided for needs special approval, studies and signatures that cost many times more than the materials themselves.

Then came the banks and the insurers: anything that isn't "conventional construction" struggles to get a mortgage or cover. And when rules for mudbrick were finally written, they demanded steel and cement inside it. That killed its one advantage: it costs almost nothing.

Nobody ever voted for "houses made of earth are forbidden." They didn't need to. Building codes are written in committees where the people selling cement, timber and construction also sit. A house a family builds itself, with earth from the yard, makes money for none of them.

Did the cement industry write the mudbrick rules with its own hand? So it's said. The documents haven't shown it. Unknown.

No conspiracy required. All it takes is everyone round the table looking after their own interest, and nobody asking whether it's the same as the public's.

But some people did ask. In the 1940s, in Egypt, the architect Hassan Fathy designed an entire village in mudbrick, New Gourna. It had vaults, inner courtyards and natural ventilation, and local craftsmen built it with techniques centuries old. The project stopped halfway, and Fathy himself wrote that bureaucracy and vested interests killed it. He didn't stop. His book, Architecture for the Poor (1973), became a classic, and in 1980 he received the Right Livelihood Award, the so-called "alternative Nobel". His student Simone Swan took the method to the Texas–Mexico border and built there with local families.

And the paperwork is starting to turn. New Mexico has its own code for earthen buildings. Since 2010 there has been an international technical standard for earth walls. In 2021 the US model residential code gained a chapter on cob, earth and straw shaped by hand, and in 2024 one on hemp-lime. Worldwide, 650 to 700 million people still live in earthen homes. In richer countries, researchers see the first signs of a revival.

The earth didn't go anywhere. The rulebook is starting to remember it. And the first step needs no permit: just learning to see it again.

Practices

1. Palm on the wall. Next time you walk into an old stone or mudbrick house, put your palm on the wall, from the inside. Compare it with the wall of an apartment block. What you're feeling is called thermal mass.
2. Ask the oldest. Ask the oldest person in your family how the family home was built: with what, how long it took, who helped, what money paid for it. Write it down before it's lost.
3. The sum. Work out how many years of salary a house costs today where you live, and how many it cost your parents or grandparents.
4. Three questions for "not allowed". Is it a law, a regulation, or just "not provided for"? Who wrote it? Who gains if it stays that way?

Politically correct statement of the dayGreece is an earthquake zone, and so are plenty of other places. Before you build anything, earth or otherwise, talk to a structural engineer.