Designed in 1962 by Jorn Utzon, best known for his world-famous design of the Sydney Opera House, it is understandably one of the most admired residences of our age. The six-bedroom house is located on a sought-after residential road in the popular Hertfordshire town of Harpenden. Internally it extends to almost 4,500 sq ft and enjoys extensive, secluded gardens.

It was originally designed by Utzon for his friend and fellow Dane, Povl Ahm, who was chairman of Arup. It was sympathetically extended in 1972 by Ulrick Plesner, an architect at Arup, and has also had a further discreet extension completed as part of an extensive and exacting refurbishment scheme carried out by the highly respected 800 Group. The attention to detail and quality of finished employed is of an exceptional standard.

The house is entered via a car port into an entrance hall. From here steps lead up to a spectacular living room. With full length, floor to ceiling glass overlooking the gardens and exquisite concrete and timber detailing. The living room is divided from the dining area by a minimal set of shallow steps. An enclosed kitchen overlooks the dining area. Also on this floor are four bedrooms, a bathroom, shower room and utility room.

Beyond the entrance hall on the ground floor is a library leading to further accommodation wing. This incorporates a fifth bedroom and an impressive master bedroom suite. The latter includes are large dressing room with bespoke wardrobes, a bathroom, sauna and the bedroom itself with double doors out onto the garden.

There is also an integral garage at the property as well as ample space for parking cars on the driveway. The gardens are extensive, forming an L-shape running to the side and rear of the house. The current owners have constructed a skateboarding facility and tree house at the far end, out of sight of the main house.

When Ahm’s family grew, he knew he needed to extend the house and so he turned to Ulrik Plesner (b. 1930), also a Danish architect who worked at Arup in the late 1960s. In collaboration with Christopher Beaver Associates, Plesner created a similar, single-storey structure that is entirely sympathetic. With Ahm keeping his exacting eye on the project, it took three years to complete.