Advocates of green building in the United States are using miniature, portable homes to exemplify the virtues of sustainable construction.

The so-called ‘Small House Movement’ eschews conventional preferences in the country for larger homes in favour of modest dwellings which emphasize sustainability and conservation. “I used to build mansions on the beach, and I’ve gone to the polar opposite of that,” said Michael O’Donovan, a builder who specialises in the…