THE theatrical home of Scottish Opera, one of the key theatres in Scotland, is to be transformed in a dramatic £11.5 million project with work starting on Monday.

The biggest redevelopment in the 144-year history of the Theatre Royal in Glasgow is to feature a bold "lantern" design from architects Page\Park, which will dominate the corner of Cowcaddens Road and Hope Street in the city's centre.

The large addition to the venerable building, a cylindrical design, will provide new foyers, bars, a box office, cloakrooms, toilets, hospitality suites and lifts to the currently cramped foyer areas.

The new building, the design of which hints at the notes on a score of music, will also provide proper wheelchair access for the first time as well as a roof- top space where visitors – weather permitting – can eat, drink and admire the views over the city.

More than 80% of the funds for the project have been secured, with the latest grant of £850,000 from the Heritage Lottery Fund, adding to nearly £4m from the Scottish Government plus funding from Creative Scotland, Glasgow City Council, individual donors and trusts and foundations.

Scottish Opera hopes its plans for the redevelopment of the building, which does not include changes to its backstage areas, will have a minimal impact on the venue's calendar of performances.

The construction process will last about 18 months, but the theatre itself will close for roughly three months, from February to May in 2014.

Although the auditorium of the Theatre Royal is Grade-A listed, the rest of the building is not, and the new Page\Park building will require the demolition of the current cafe area and hospitality areas, as well as building on the currently empty patch of land between the theatre and neighbouring offices.

The new theatre will have three main entrances and theatre-goers will access their seats via a dramatic spiral staircase. It will also include spacious foyer areas and window bays – which can be sponsored – for gathering and enjoying refreshments.

One of the main problems with the old theatre – its often stifling atmosphere – will be addressed with a new climate control system.

The Theatre Royal was built in 1867, and its present auditorium is 116 years old. From 1957 to 1974 the theatre was the home to STV, but it is now owned by Scottish Opera and has been managed by the Ambassador Theatre Group (ATG) since 2006.

Alex Reedijk, the director of Scottish Opera, said: "Our vision is to open up the theatre to become a social hub, somewhere people can gather with friends for great coffee during the day, enjoy outstanding performances, learn about the performing arts, and discover the heritage of this beautiful theatre."

Mr Reedjik said the financial stability of the opera company, currently celebrating its 50th birthday, was key to the planning of the project, which he said he hoped would be "big but intimate" inside.

"I don't think we, as a company, would have contemplated this if we were not in good order [financially]," Mr Reedjik said. "We have had to do that in order to think about the longer term, and because we are in good order, that has encouraged people to support us, because they would not have wanted to if there was any doubt over who we were.

"So we can embark on this ambitious project, and people respond to ambition.

"Here is a chance for Scottish Opera, in time for the Commonwealth Games, to create a building which has a fantastic legacy for the 21st century, and also reflects those 19th-century values that you can see in the city centre, in the Mitchell [Library] and Kelvingrove [Museum] – buildings that were built when Glasgow was at the height of its power."