Ty Mawr won out over Sydney's Olympic stadium

The house has beaten prestigious projects like the Bodleian Library in Oxford, the Tate Modern gallery in London - opened in May by the Queen - and the stunning arena in Sydney which recently hosted the Millennium Olympic.

The award was announced by the Prince of Wales at a ceremony at London Docklands.

The house - built in 1460 - was an interesting ruin but it has been restored, opened to the public and there are plans for it to be used for community events.

In the restoration a series of roof trusses were supported on a forest of scaffold poles, so that the building could be transformed into a complete and occupied residence, now granted Grade One listed status.

Tate Modern was opened by the Queen in May

Powis Castle Estate will look after the building on a long lease.

RICS judges said the work had been carried out with "meticulous attention to detail".

They added that there had been "exceptional use of interventionist techniques wherever possible".

RICS President Jonathan Harris, said: "It is a wonderful example of what dedication and application can do, taking a building of imminent collapse, reconstructing with the greatest care to emphasise its delightful character and location."