A survey has revealed the water damage to the Hill House in Helensburgh.
The property, designed by Charles Rennie Mackintosh, has been threatened by the effects of water penetration.
Owners the National Trust for Scotland (NTS) and Historic Environment Scotland used infra-red technology to show how damp and water has damaged the building.
A mesh structure is being constructed around the building to protect it from the weather while it is restored.
A previous infra-red survey from 2003 has been combined with the new images and further surveys to allow conservationists to pinpoint the worst affected areas and understand why the property's condition is declining.
The technique highlights differences in surface temperature, which shows where moisture from decades of wet weather has accumulated within the building.
The Hill House was finished in 1904, but a century of Scottish weather has taken its toll.
'A home for the future'
Rennie Mackintosh had envisioned it as "a home for the future" and used experimental building material - which has allowed water to soak into the building.
Richard Williams, of the National Trust for Scotland, said: "These surveys reinforce what we already knew about the house, which is that it is very damp and has considerable issues that need to be overcome.
"Due to the design of the Hill House, there are many ledges, wall heads and chimneys that have had a history of many attempts to remedy, yet this problem continues.
"We're also now have additional areas of concern. We have also been able to see the direction that the water is travelling in some of the rooms, in particular in the exhibition room, where there was already clear damage.
"The works to create the 'box' are now well under way and we are grateful to the many individuals who have generously donated to help us to tackle these problems. The intention is that the structure will provide a temporary respite for the Hill House pending a long-term solution to the water ingress being found."
The house and gardens are currently closed to the public but are expected to reopen in late spring.