The $142 million makeover of the worn-out Gaillard Municipal Auditorium into a top performing arts venue, exhibition space and city offices is officially a go: Construction is set to begin next month and finish by early 2015.

Funded by an equal mix of city and private dollars, the new Gaillard Center has been emerging from drawing boards for more than two years, but Tuesday’s unanimous votes by Charleston City Council marks the single biggest step of making it a reality.

Mayor Joe Riley noted it will be the largest construction project in the city’s history and noted there were few changes in the project approved two years ago.

On Tuesday, City Council specifically authorized a construction-manager-at-risk contract with Skanska Trident Construction, a joint venture, for $110 million, plus a $650,000 city emergency operations center there and $1 million in green- space upgrades along Calhoun Street. It also approved a letter of support from the Gaillard Performance Hall Foundation, which is raising $71 million in private money toward the work.

Reach Robert Behre at 937-5771.