"It's quite a bit above the sea level," said architect Dr Mike Austin of the Chapple House. "Storm damage will always be a potential problem but there has never been any in 50 years. It's not a big area of house or wall and wind and storms have less impact on small walls."
Ruth Foreman, co-owner with Russell Cassey as executors of the late Bill Foreman's estate, agreed.
"Some people love the idea of being connected to the elements and here, you truly are," Bill Foreman's daughter said of the home, accessed via gondola.
The house built by Ian McIntyre is widely acknowledged as architecturally important, appearing in books and magazines. It is not listed but has a Heritage New Zealand covenant on its title "to protect its architectural values," the council says. Austin was an architecture professor at Unitec.
Foreman's Thorne Bay house is being marketed by Graham Wall, who says it could fetch up to $7m although the council valuation is $4.8m.
"Nothing on Takapuna beach has sold for under $6m in the last two years. This house is 3m above mean high tide," Wall said of its proximity to the ocean.
The council's Takapuna-Milford Walk guide tells how Austin was hired by Win Chapple in 1967, seeking a straightforward place, not ostentatious, fitting in with the existing natural landscape.
"Gnarled pohutukawa are on the lava flow rock shoreline site." Rocks were collected by the family and "stonemason Sven Hansen built rock walls 20ft from the house to separate it from the sea. Neighbours commented that on stormy days it appeared as if the house were floating as the sea washed over the rocks," the council guide says.
Belinda Storey, a climate economist, says coastal buildings exposed to one-in-100-year events are likely to become uninsurable "and in some cases uninhabitable within the next couple of decades as even small changes in seal levels will significantly increase the reach of coastal storms."
Without insurance, banks might not be able to grant mortgages to buyers needing finance to buy homes closes to the water, she predicts.
"Insurance is a prerequisite for securing a mortgage. Therefore, once insurance is unavailable, property owners will find it difficult to borrow money to purchase a property or to pay for physical defence of the property. Furthermore, since insurance policies are renewed annually, insurance retreat can occur during the term of an existing mortgage," Storey says.
Austin said a more obvious site for the Chapple House would have been further from the sea, up the cliff: "But it was a deliberate move to come down here, to engage with the elements."
However, he also recalled the home's floors laid during the Wahine storm when water was visible below and "waves were going to break on top of the house".
Ruth Foreman said her father lived there from 2002 till his death last August, aged 90. He had loved it, she said and the structure was partly adapted to suit him.
The council said the modernist design was special.
"The house has historic significance as the former home of Win Chapple and as the embodiment of a mid-20th century design process that was documented by Chapple in a house log.
"In the log book, the architect expresses his concern about doing justice to the site and the client records the daily events of the construction period. Further research may underline the historic significance of a landmark modernist house being commissioned by a woman for her use alone."