Laura Ryan calls it the impossible house. After seven years of intense technical drawings and conundrums, the fund manager is bracing for a kitchen that runs out of water, toilets on the fritz, and candle-lit dinners.

By day, Dr Ryan is trading basis points for bonds and derivatives bigwig Ardea Investment Management. At night, she is building an off-the-grid house of just 104 square metres in Sydney’s Newtown, with plans to move in mid-year.