Kevin McCloud was forced to admit guests had surprised him during tonight's Grand Designs.
The property expert held his hands up and said he never expected scientist Andrew and wife Margretta to pull off their self-heating eco-home - which he had dubbed an "uninhabitable science project."
The Buckinghamshire project dragged on for more than three years, set back to innumerable issues including the pandemic.
Andrew explained early on in the episode that he aspired to build a home into the ground and covered in layers of insulation and topped off with an "ancient grassland" layer - intending it to build up a store of heat, enough to chase away the chill during the winter months.
Kevin was sceptical, and gave his unfiltered verdict after one viewing.
But when he visits at a later date, £310,000 further down the line, he's startled at what he sees.
"This project was never about aesthetics was it?" he asked.
"It was always an experiment, but I am pleasantly surprised."
Kevin added: "All that sun-trapping glazing is dazzling, a mirror to a luscious landscape.
"The oiled cedar cladding, black frames, and white stucco are like a throwback to Andrew's youth of the 1970s."
And referencing the grass on the roof, Kevin laughed: "Although from some angles it looks like it has been magically cross-fertilised with a shaggy Celtic burial mound."
Some viewers weren't sold.
"If my central heating was set at 16 my missus would be packing my bags #granddesigns," one tweeted.
Another queried: "So in the summer when it’s hot he has to keep the doors shut? Genius #granddesigns."
But others were sympathetic to Andrew's environmental concerns, with one penning: "We do need people like Andrew, caring for the environment on a large scale."
They added: "Most of us can't really be bothered apart from recycling."
