Roger moved into Six Pillars from nearby Dulwich Village in 1998 with his wife Deirdre and their three young daughters. They loved the fact that the garden backed on to a wooded hill and nature reserve. "It gives the house a wonderful rural feel," Deirdre says. "It's hard to believe that Victoria and Blackfriars are 15-minute train rides away."
Above all, the Trapps were impressed by the design. "It's playful and there is a lot of humour," Roger says. "It's presumably called Six Pillars because of the six support columns at the front. There is in fact a seventh pillar inside. I'm pretty sure that's an architectural joke - an oblique reference to the Seven Pillars of Wisdom."
The house, built in 1934, was largely inspired by the work of Le Corbusier. It is Grade II* listed and was designed by Berthold Lubetkin's influential Tecton practice. Lubetkin is best known for his design of the sweeping concrete penguin-pool at London Zoo.
The original drawings for Six Pillars were the work of Valentine Harding, one of Lubetkin's employees and a rising star of British architecture who died in the Second World War.
When the Trapps acquired the house seven years ago, it was in desperate need of repair. However, its listed status meant they had to be cautious. They enlisted the help of John Winter, an architect who specialises in restoring modernist buildings.
The first priority was to ensure it was structurally sound. They replaced the flat roof, repaired and reinforced the concrete balustrades and replaced the metal windows. The crumbling York stone walls and paving at the front were replaced with simple white rendered walling.
For the interior, the Trapps aimed to combine simplicity with functionality and sympathy for its history, but at the same time to feel free to add a few flourishes. "We followed John Winter's advice. He told us that we shouldn't regard it as a museum, but rather enjoy it," Roger says.
The original parquet flooring in the drawing room was retained and extended into the living room, dining room and breakfast area. They kept the chrome fireplace in the living room but disabled the "lethal" electric bar heaters in the first-floor bedrooms.
They ripped out the kitchen, tiled the floor and installed free-standing stainless-steel units and appliances. "We like entertaining lavishly and giving large dinner parties for our friends, so we decided to install a real cook's kitchen," Deirdre says.
Minimalist furniture and fittings - dining room suite and sofas by the Finnish designer Aalto, simple Scandinavian lighting and Lucienne Day repro fabrics from the 1950s for the curtains - complemented the mood of the place, as did the neutral white colour scheme enlivened with bold swirls of cornflower blue around the living room pillar and twin flights of spiral staircases.
The house was originally commissioned by Jack Leakey, a headmaster at a local school, as a home for his wife and himself. The Leakeys were childless and split the first floor into mirror-image his-and-hers quarters, joined by a roof terrace, with each wing with two bedrooms, dressing room and bathroom.
The Trapps say the layout works equally well as a family living area. That is another thing they like about Six Pillars - its adaptability. "It's very flexible and versatile," Deirdre says. "There are a lot of useful nooks and crannies that can be used to make a playroom for kids or as somewhere to stash the utilities."
The symmetry continues on the top level, where a single room - now a study - juts out like a beacon in the middle of an enormous roof terrace.
It's this symmetry, say the Trapps, that they'll miss most when they move to Sevenoaks to be closer to their children's schools. "It's a fantastically proportioned house," Roger says. "Every-thing is perfectly aligned. It creates a wonderful sense of calm and balance."
Get the spec
What's for sale: Five-bedroom house over three floors in a leafy setting with secluded south-east facing garden and extensive dual-level roof terraces overlooking woodland.
Serious kit: Industrial-style kitchen, parquet floors, many original features, horseshoe-shaped driveway with off-street parking, two garages, extensive storage space, concealed cupboards and closets in first-floor passageways.
How big? About 270sqm, including living room, kitchen, dining room, first-floor gallery with mirror-image wings, two bathrooms and a penthouse office area.
Buy it: The Modern House, 01420 520805; £1.5m,Reuse content