Melvin Felix PS 122 at 150 First Avenue.

After months of delays, the overhaul of Performance Space 122 is moving forward.

A work order filed last week and pending approval by Department of Buildings paves the way for construction of two brand-new performance spaces in the venerable theater, which will cost an estimated $15.1 million. The plans call for more than 9,000 additional square feet to be added to the building at 150 First Avenue, all paid for by the city.

PS 122’s artistic director, Vallejo Gantner, said Wednesday that he was “delighted” that work will soon be underway. Since the city has already funded work on the building’s facade, replaced old energy-inefficient windows, and gotten rid of asbestos and lead paint, he estimated that the project’s full cost will be more than $20 million. He’s thankful for every penny.

“I think the city is kind of amazing that, in a time like this, they’re investing in cultural activities,” Mr. Gantner said. “The fact that it’s happening at all is such an amazing thing.”

In February, Crain’s reported that delays in the permit process had stalled the renovations, which were scheduled to begin last summer. But Mr. Gantner didn’t mind waiting, given the money invested by the city.

“It would be absurd for us to worry about an extra month here and there,” he said.

A formal groundbreaking is expected in the fall, along with a fundraising drive for $1 million. The new facility, which will improve on the organization’s old space with more seats, a lobby, and new equipment, should be open by the 2014-15 season. Until then, the organization will continue to host performances in other venues around the city.

“We’re counting our blessings, and we’re having a good time out of the building,” Mr. Gantner said.

The organization is now planning shows in the Lower East Side, in Long Island City, throughout Brooklyn and in a half-dozen other locations. The experience has already changed the character of the 30-year-old arts center known as a haven for experimentation.

It won’t be enough for PS 122 to just be a “bricks and mortar institution,” Mr. Gantner said. “We really intend to continue to present things outside of that space as well. For our artists, it’s been very compelling.”