So what makes this apparently simple add-on to the rear of a late-Victorian terrace family home the winner of an award for projects costing less than £250,000?
When the couple first decided to replace an old lean-to at the un-modernised house they bought in Ravenscourt Park in 2008, they declared war on the ordinary.
"I just didn't want to add another glass box to a suburban house," says Gareth, a furniture designer.
Fortunately, his wife, an architect, agreed. Gareth adds: "We both wanted something that would have identity. This was never purely about adding floorspace."
The problem that inspired the project was the lack of a family-size kitchen in the house for them and their two young daughters.
Says Lucy, who is more used to advising on larger-scale projects, including construction in the Olympic Park, says: "There was a tiny breakfast room and the kitchen was a two square-metre scullery at the back of the house.
"As a mother, whether you like it or not, you spend so much of your life in the kitchen and this one just didn't work."
The couple, both 40, hired architect Nick Hayhurst, of Hayhurst and Co (hayhurstand.co.uk). They felt they needed outside help partly because of the complexity of the site. Their house sits at the end of the terrace and is wedge-shaped, narrower at the street side, opening to wider space at the rear. It also sits on a slope.
Their garden is north facing, so lack of light threatened to be a problem.
But given her professional expertise Lucy worked closely with Hayhurst on the plans, which then breezed through the planning process in only eight weeks. Work on the nine-month project began early last year.
However, this was a tricky project and it was never going to be a quick build. For starters, they needed to dig down about half a metre to give the new kitchen high ceilings. That left the new extension slightly lower than the garden level, but meant that a window seat overlooking the garden could be positioned at exactly the same level as the lawn.
The extension is double aspect, with huge sliding doors leading on to a new terrace built at its side.
The ceiling slopes upwards to this side of the room — another deliberate move in order to give space for the largest possible of sliding windows to take advantage of what was going to be the sunnier side of the room.
A new utility room was built under the stairs, and Gareth (garethlangdon.co.uk) took charge of building the kitchen himself using tough, sustainably sourced iroko wood. The same timber was used to clad part of the extension, laid in carefully cut panels.
Precision is the word here. The exact shape of the 26-square metre extension defies description, not quite a parallelogram but not entirely a trapezium either.
The floor is a herringbone of white tiles — a motif that continues out on to the terrace. Outside, as well as the iroko timbers, slate laid in painstakingly perfect rows completes the cladding. Above is a green roof of meadow flowers that has given a display of poppies, daisies and scabious since the spring. In future the family hopes to keep bees on it.
The overall effect is of a completed, hugely detailed jigsaw puzzle — one which clearly set a remarkable challenge for their builders, Rebuild London (rebuildlondon.co.uk) to put together.
Says Lucy: "Though the project was very overwhelming in one way, I think that the builders enjoyed it, too. They took a great deal of pride in it."
The project — including the garden — cost about £150,000 in total, so it was not cheap, but it has future-proofed the house for the family. And they feel the extra expense of a highly technical build has been worthwhile — something they enjoy looking at daily.
The secret of the project's success, Lucy believes, is the sheer degree of thought and care that went into it. "There has not been one decision that has not been thought about and re-thought — everything has been considered and reconsidered and that is how you achieve an incredible richness."
And an award-winning result.
Photographs: Simon Maxwell