NEW images show the severity of water damage to one of Charles Rennie Mackintosh’s most famous creations.

The thermographic images of damp and water damage to The Hill House in Helensburgh have been released by the National Trust for Scotland, which owns and looks after the historic building.

A new three-part survey, carried out in a joint effort by the NTS and Historic Environment Scotland, has showed up additional areas of concern for the building.

These include large sections of harling - the rough cast wall finish - that have come away from its walls, where damp is now gathering and growing, and internal walls which the Trust had not realised were so damp.

The NTS is in the process of surrounding the building with a mesh structure to protect it from the weather: this process is nearly three-quarters complete.

A previous survey was carried out in 2003 at the site, and now the new infra-red images have been combined with a 3D digital survey and microwave moisture readings.

Infra-red thermographic (IRT) imaging records differences of surface temperature, which gives an indication of where moisture from decades of “almost constant wet weather” has been retained within the building fabric.

The Herald:

The red and orange colours show warm temperatures, the blue and purple areas show the cold, damp areas of the building.

Since the Hill House was completed in 1904, years of wind and rain have caused significant issues with water ingress.

The NTS plan to surround the building with ‘The Box’, a protective mesh structure to stop water getting in, and allowing the house to dry out and repairs be made.

Richard Williams, general manager for Glasgow and West at the National Trust for Scotland, said: “By combining the infra-red thermographic survey, the 3D scan and the microwave readings we have a very powerful tool to aid our technical understanding of the complex problems at The Hill House, and a robust baseline before we surround the building with its protective shield.

“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.”

Dr Ewan Hyslop, head of technical research and science at Historic Environment Scotland (HES), said: “We’re very pleased to offer our skills and expertise to support the National Trust for Scotland in this important project.

“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 are currently closed to the public.

However, it is expected to reopen in late spring this year.

When the house re-opens, it will have raised walkways around the exterior of the house and over the roof.

Mr Williams added: “The works to create the ‘box’ are now well underway 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, in conjunction with our Mackintosh partners.”

Mackintosh designed the house for Glasgow book publisher Walter Blackie, with his wife, the artist Margaret Macdonald, and it was built from 1902-4.

The NTS have said that since 1902, the Hill House has been “battered by 193 days of rain per year” on average.

The extent of the damage over the years led the NTS to announce the box plans.

Last year, Rhiannon Spencer-Jones, Fundraising Manager for the Hill House Appeal, said that the bx will be a “semi-transparent shelter around the main house, consisting of a steel roof and a frame encased in a semi-permeable metallic mesh.

“It has been designed specifically for the Hill House, meaning that the garden within the Box is maintained and protected, trees will continue to grow inside the Box, as well as allowing the building to remain visible.”

It could take three years for the house to “dry out”.

A “long lasting solution” to the building’s issues would then have to be formulated and be put into action, which could mean the box will be in place around the house for up to ten years.

The 150th anniversary of the birth of Charles Rennie Mackintosh was marked last year.

It saw the re-opening of the Willow Tea Rooms building in Glasgow - Mackintosh at the Willow, but also the disastrous fire at the Mackintosh Building at the Glasgow School of Art.