FARMINGTON — Barring unavoidable weather delays or unanticipated material shortages, the new gym at Mt. Blue High School is set to open for students in about eight weeks.

It’s the latest benchmark in the three-year, $64 million renovation and expansion.

“The contractors are expecting to have the locker rooms open toward the end of February, and the gym open by March 1,” architect Lyndon Keck of PDT Architects said.

“The unfortunate collapse (of the gym roof trusses) scared all of us, and the contractor is trying to get back on track. They are doing a good job. We are pleased,” Keck said Tuesday.

One worker had minor injuries in the construction accident in September. The collapse delayed work on the gym that had been set to open in November.

The second phase of the project will focus on opening the two-story classroom wing and the central, shared facilities that include the library and food court by the start of the 2012 school year, he said.

“That will be our next big deadline,” he said.

For spring sports, the only playing field that will be ready for practices this year will be the new multipurpose field built last year down the Seamon Road. The turf on the other fields will not be established until the fall of 2013, which means games will continue to be held at other venues in the district.

The mild weather at the end of November and over the first three weeks in December allowed the contractors to pour concrete foundations for the new wings before the hard freeze of winter, Keck said.

In his monthly report that appears on the Mt. Blue Regional School District’s website, www.mtbluersd.org, he writes that the gym has now been enclosed and is set up with temporary heat, and the steel and roof deck welding has been completed and inspected by a certified welding laboratory. Also, roof insulation and a waterproofing membrane are about 50 percent complete on the high gym roof.

Temporary heat has been installed in the locker room areas, and the roof insulation there is completed.

Among the other work going on is preparation for the geothermal heating system, the wood chip boiler complex, and pouring footings and foundations for the two-story academic wing, Keck wrote.

He said Mt. Blue administrators meet every two weeks with the architect, contractor and representatives from the state agencies that oversee the construction. The team reviews the progress schedule, as well as job site safety as it affects students, faculty and workers.

Next month, structural steel and the concrete firewalls in two of the wings will go up, and cranes will be set up in the courtyard and on the southern construction road to place the structural steel. That phase will take about one month.