‘Earthships’ are a type of low-tech buildings, conceived by Michael Reynolds in the 1970s, which can be constructed by amateurs using only recycled, locally sourced, or sustainable construction materials. Combined with ‘passive solar’ design principles, which make use of the orientation of the sun to maximise heat gains and minimise losses, Earthships present a highly sustainable and circular building philosophy. But how well do these design principles from the 1970s hold up in today’s world? We analysed the thermal performance of an Aardehuis – Netherlands’ first community of Earthships – to find out.