The first steel beams for a shelter to protect one of Charles Rennie Mackintosh’s most iconic works have been put in place.

Work is being carried out on Hill House, a property in Helensburgh, Argyll and Bute, described as Mackintosh’s “domestic masterpiece”, to help preserve it for years to come.

The project will see a “box” frame erected around the house before a fine perforated mesh, designed by award-winning architects Carmody Groarke, is added.

Preliminary sitework began in November 2018, with two months of preparation for the installation of the steel frame of the structure.

Since it was built over a century ago, Hill House has been absorbing rain, putting the building and its unique interiors at risk.

The semi-permanent enclosure will provide shelter to the structure, letting it dry out after years of disintegration and allowing for further conservation work to take place.

As well as protecting the building from the weather, the “box” will give visitors the chance to get a new perspective on Hill House from elevated walkways looping around the building.

The house and gardens will be closed to the public during the construction of the “box” but are expected to reopen in late spring this year.

Richard Williams, of the National Trust for Scotland, said: “Seeing the box take shape is an extraordinary feeling and a significant milestone in our charity’s rescue effort to save the Hill House.

“After years of planning we can really start to see the scale of what we’re doing here, for the love of the building and where it stands in the history of Scottish architecture.”

Thousands of people have donated to the charity’s Box the Hill House campaign, which launched in February 2018, with a total of £1.2 million raised so far.