The new fire alarm at Bozeman's Hawthorne School is so excruciatingly loud and painfully piercing, it's sure to drive every child and teacher out of the building in the event of a fire.

Teachers and construction workers walked around with fingers in their ears Wednesday afternoon, while the city fire marshal tested the new system.

The alarm is just one small part of a $2.5 million construction project that's intended to bring the 1938 building's electrical and ventilation systems up to 21st century standards.

Construction on the $500,000 first phase began in June, but it won't be finished before classes begin Monday, said Jared Hoesel, project engineer for BNBuilders Inc.

Hoesel said a lot of effort is being taken "to ensure students are safe" as construction is completed.

Starting Monday, construction crews will move to night shifts. Building materials will be fenced off from Hawthorne's playground, and covered walkways will protect children, he said.

This part of the project was originally supposed to be completed Sept. 30, Principal Robin Miller wrote in a memo to parents.

But Hoesel said workers ran into some unexpected problems - such as concrete parapets on the roof that were crumbling so badly, they could be pulled out by hand.

Hoesel said he expects the job will be finished by early October. Meanwhile, it has created about 30 construction jobs.

Miller assured parents that the work will be done in a way that won't affect the regular school day and will keep students safe.

Motorists driving by on North Rouse Avenue can see steel framing rising on the north and south ends of the school. The framing is for two new rooms on the second floor, said Kevin Barre, Bozeman schools facilities director.

The new rooms will house modern heating and ventilation equipment, which will be installed next year during the project's second phase. The rooms will also provide some additional teaching space, Barre said.

A new electrical system is being installed to increase capacity for computers and to run the new air-handling system. The Hawthorne project also includes renovating and enlarging restrooms, installing new windows and reroofing the gym.

Similar upgrades have already been made at Irving and Longfellow schools, also built during the 1930s.

More than a decade ago, school officials considered abandoning Bozeman's small, Depression-era schools in favor of larger, modern buildings to save money on repairs. But parents and community members came out in favor of keeping the older schools to provide a more intimate school environment for kids and to preserve Bozeman's older neighborhoods.

Hawthorne's renovations are being paid for with local tax dollars from a building maintenance levy approved by Bozeman elementary district voters a few years ago.

Hawthorne's is the biggest school repair project undertaken this summer, other than completion of Bozeman High School's renovation, Barre said. Other summer projects included reroofing Whittier School for $160,000; repaving parking lots at Willson School, $90,000; redoing the gym floor at Morning Star School, $49,000; and new gym lighting at seven schools, $43,000.

Gail Schontzler can be reached at gails@dailychronicle.com or 582-2633.