Thermal images disclose extensive damage to The Hill House, Charles Rennie Mackintosh's 'domestic masterpiece'

Thermal images have revealed the damp and water damage to Charles Rennie Mackintosh's "domestic masterpiece" is worse than previously thought.

The Hill House in Helensburgh was Mackintosh’s vision of a "home for the future", but decades of wind and rain have caused the sandstone structure to be dissolving under its cement render.

The National Trust for Scotland (NTS), who own and care for the 1904 property, and Historic Environment Scotland (HES) conducted the survey while a giant £4.5million box is constructed to shield the building from the elements.

State of the art infra-red thermographic (IRT) imaging was used to indicate where moisture is retained within the building fabric.

The images, which record differences in surface temperatures, were combined with new 3D digital survey and microwave moisture readings and a previous IRT survey carried out in 2003.

The three surveys allow building conservators to pinpoint areas of damp, and further understand the declining condition of the property.

Richard Williams, NTS general manager for Glasgow and West Scotland, said they would provide a "robust baseline" for the building's condition before the protective shield is completed.

He 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 also now have additional areas of concern, such as large sections of harling that have become disengaged from the walls where damp is accumulating, and internal walls we hadn’t realised were so damp.

"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."

He said the construction of the box was "well underway" and it would provide "a temporary respite" pending a long-term solution being found to the building's problems.

Dr Ewan Hyslop, head of technical research and science at Historic Environment Scotland (HES), said: "Hill House is a Mackintosh masterpiece, and this project is a great example of how we can use innovative technology to better understand the risks to historic sites such as this and inform work to conserve and protect them."

The house and gardens, which were built for the publisher Walter Blackie, are currently closed to the public but are expected to reopen in late spring this year.

Preliminary site work began in November last year for the installation of the steel frame of the mesh "box" structure

This will also give visitors a new perspective on the building from elevated walkways looping around it and opportunities to get to rooftop level.