Underhill House, an eco-home in the Cotswolds that appeared on Channel 4’s “Grand Designs,” is being marketed for sale at £3.25 million. The property was originally built at an estimated cost of about £600,000 and is presented as England’s first certified Passivhaus home, a building standard designed to achieve very low energy use through airtight construction and high insulation. The listings highlight that the home’s Passivhaus certification means it is effectively airtight, which can reduce heating and energy demand compared with conventional housing. Details reported across sources focus on the home’s on-screen profile and its energy-efficiency claims rather than on who currently owns it or when it was built beyond the stated build cost. The information available indicates that the main selling point is the property’s certified performance and, as described in reporting, relatively low running costs, reflecting the intent of the Passivhaus approach.