Wright masterpiece in danger of collapsing

It sits among the woodlands of the Allegheny mountains in Pennsylvania, hanging over a creek: a testament to the vision of one of the world's most famous architects.

But Fallingwater – the modernist creation of Frank Lloyd Wright – is in danger of collapsing, unless a $11.5m (£7.9m) renovation project can save its dangerously sagging frames and cracking beams.

Fallingwater was built in 1935 for Edgar Kaufmann Snr, a Pittsburgh department store tycoon, and his wife. Their son donated it to the Western Pennsylvania Conservancy in 1963 when it was opened to the public. The house now attracts 140,000 visitors annually, who are drawn by the built-in furniture, North Carolina walnut veneer and Wright's trademark clutter-free interior.

But the property is suffering from a problem rooted in its alluring design. After completing his design for the property, Wright argued with the engineering firm brought in to build it. The engineers wanted to make the floors stronger: Wright said this would make them unsupportably heavy.

As it transpired, the engineers were proved right. The beams in the house are cracking, the floors are sagging and the house is now being supported by trusses to stop it falling into the fast-moving mountain stream it sits astride.

Lynda Waggoner, the director of the property, told The New York Times: "It has deformed over a very long period of time, almost 70 years."

A plan to try and save the property was launched two years ago. While the house was built for just $155,000 – which included Wright's fee of $80,000 – it is estimated that it would cost almost $12m to carry out the repairs. Work will begin in November and is due to be completed by next April.

Many experts are not surprised that Wright's breathtaking creation requires some work. Robert Stern, dean of the Yale School of Architecture, said: "When you're involved with an experiment, you're often ahead of the curve. The rewards are great, spatially and aesthetically, but later on things have to be done."

Some of the funds for repairing the property have been raised by an increase in the admission price and by allowing visitors to see the problems that exist. Aficionados unable to make the trip to the house will be able to see how the repairs have been carried out by buying a video of the project.

Quite what Wright would have thought of the repairs to his most famous emblem is unclear, but he certainly seems to have thought it worth saving.

Some 20 years after completing the design, he described it thus: "[It's] a great blessing ... I think nothing yet ever equalled the co-ordination and sympathetic expression of the great principle of repose where forest and stream and rock and all the elements of structure are combined so quietly that, really, you listen not to any noise whatsoever although the music of the stream is there. But you listen to Fallingwater the way you listen to the quiet of the country."