What you also notice is that in the field below the house is a shapely, mature lime tree. And that the house is exactly on axis with this tree, pointed at it like an arrow, bilaterally split around the axis. The thrust and bulge of the spine - which starts off as a relatively narrow and low hallway, and swells into a double-deck cabin-like sitting area overlooking the view - shoulders the steel-framed boxes of the main house structure aside, so they are slightly splayed. This splaying, carried through to the main façade, serves to take in the extent of rural land commanded by the Blases. Inside, by skewing what would otherwise be a relatively conventional large rectangle of double-height living space, it sets up a geometrical dynamic involving diagonal views through the house.

"We had our first briefing meeting in 1996," recalls Daniela. "Nick gave us his talk about Charles Eames, simple materials and so on. We like Charles Eames, so that was OK. In November, they came back with the model. They said, 'the middle part isn't quite worked out yet'". And she produces that first model, a wooden one in a box. True, the middle isn't quite worked out. There's a cockpit-like thing at the front with a somewhat vestigial tail flicking back through the house. But the big moves are all there. It's the Spine House.

Frank and Daniela seem to regard Nick as a kind of wise uncle. A story told by both sides concerns how their father, having decided he needed a new factory and having researched contemporary architects by visiting their buildings incognito, suddenly turned up at reception in the Grimshaw London office one day back at the end of the 1980s, and announced that he wished to commission a building. At first, nobody believed him. The story goes that Nick, a man of disciplined habit, was in a design meeting and reluctant to be interrupted by someone who hadn't made an appointment. Finally he relented, and thus began a classic architect-client relationship.

The trans-generational thing works on both sides. The Grimshaw job architects on the Igus factory, Mark Bryden and Martin Wood, subsequently set up their own practice, but kept close links with their former boss. Recent phases of the Igus masterplan have been handled by Bryden Wood. And when Nick had persuaded the younger generation of Blases that they needed a chill-out zone of their own, it made sense to keep Bryden Wood involved there, too. They knew the territory. So they handled the detail of the house. In this uncommonly civilized fashion, the job was shared. Grimshaw, as architects of his standing are wont to do, likes to get his teeth into the odd small, personal project after years of steadily larger and more time-consuming schemes culminating (while the Spine House was being built) in the Eden Project. The younger men found themselves working on an unusual prestige job. The Blases got a lot of architectural attention. The way it panned out, everybody got what they wanted.

If Nick was the wise uncle, then, as Martin Wood puts it, Mark Bryden became the "surrogate son" in this intimate relationship. No question that the Spine was Nick's concept, says Wood. They'd tend to go away and work things up, introduce some elements of their own, and then return to Grimshaw's office for a design session. So for instance, Bryden Wood persuaded Nick not to have the roof stepping down the site, since that would lead to worryingly complex junctions with the spine. Instead, the house is sunk into the slope of the hill, and the roof remains a single flat plane, but for the zinc-clad form of the spine running down the middle. Then again, says Daniela Blase, when Bryden Wood proposed that the aluminium privacy and sunshading louvres along the flanks of the house be set horizontally, Nick took one look and turned them vertically. Thus the design evolved. "It was a good working relationship," says Wood. "And not that far removed from a college crit."