Excitement is building as Helensburgh’s Hill House moves forward in planning to be a glowing example of design that will survive long into the future.

The star Charles Rennie and Margaret Macdonald Mackintosh structure continues to dry out under the metal box after decades of water ingress.

At one point, the National Trust for Scotland (NTS), which has owned and run the site for 40 years, warned it could dissolve “like an aspirin”.

Liz Davidson is project manager at the Hill House and said leaks at the building had been reported as early as 15 years into its life.

“It’s a fantastic building that never should have been put out in the rain,” she told the Advertiser.

"It's a truly extraordinary building in the west of Scotland in a period of exacerbating climate change."

Helensburgh Advertiser: Liz Davidson is project manager at Hill HouseLiz Davidson is project manager at Hill House (Image: Newsquest)

Built for the Blackie family, it is now 120 years old - but Scottish weather has not been kind.

Liz described it as "cream cheese architecture" that Charles Rennie Mackintosh then carved into.

That has created unique design challenges to ensure water can drain off the building.

The two and a half layers of render and paint over the red sandstone have hairline cracks, acting as straws drawing the water into the building.

Helensburgh is now very familiar with the metal box put over the home to allow it to dry out - and it is working.

Liz said the box has a limited lifespan, and planning permission, so 2028 is the absolute latest it can be removed.

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Before then, detailed analysis is underway, with samples of the render going to Dundee University to find out what it's actually made of - suspected to be a mix of sand, agregate, cement and some additive.

What render is used next over the stone to achieve the same look but protect it for decades to come is still to be determined.

Though the plans are moving forward with momentum, it is not a quick process to get the building back in a public state.

The goal is to remove all loose material in early 2024. With the stonework exposed, it will need more time to dry out even further, leaving time to find the best new rendering possible by 2025.

Liz said NTS recognised Hill House would need cyclical maintenance because of its unique design.

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The stone under the render is in "pretty good condition" and it is regaining its strength now that its skin is drying out.

And the detailed study of the outside of the building is being mirrored inside, with some bedrooms potentially having been painted over the original colour and stencils.

In the past century, windows had been painted shut. The 18 fire places, which would have helped air flow in the building, haven't been in use but could provide solutions for its future.

"The project is already on a wave that’s building," said Liz. "I think the inside will be more authentic.

"I'm excited to see it as Mackintosh and the Blackies saw it."

The wonderful gardens of the home - once used to also feed the Hill House - were "trashed" when the box went up, and will be again when it comes down. But Liz said they will be re-instated, and there could be an opportunity to create a more engaged space.

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And she wants more recognition of the role of the women at the site - the Blackie women and artistic women such as Margaret Macdonald Mackintosh.

"They were absolutely equal partners," she explained. "There’s a lot of social history. It was a really happy family home. There’s all of that side to explore."

NTS is also looking at a potential visitor centre and improvements to parking, but that's dependent on the conclusion of a business plan. That's before a design and consultation with neighbours could happen.

In the meantime, there is a twin focus on continuing to save the Hill House for the future, and to celebrate what it achieved.

Liz said there was an element of "local guy makes good" but NTS wants the Hill House to matter to everybody, not just design fans.

"Charles Rennie and Margaret were creating magic," she said.

"Design and the beauty of design doesn't have to be precious stones. He is Scotland's absolute arts and craft maestro.

"You can just stand in Hill House and absorb it. You can feel it as a house.

"It just keeps on surprising you."