WEYMOUTH — For the third time in less than three months, a housing development under construction in Greater Boston has been destroyed by fire, raising fresh concerns about the safety of wood-frame buildings that have become a mainstay of the region’s real estate boom.
Investigators were working to determine the cause of the Thursday morning blaze at a 50-unit condominium in the Union Point development on the former South Weymouth Naval Air Station. The four-story building caught fire shortly before 3 a.m., and the damage was estimated at $20 million to $30 million, according to its builder, Pulte Homes.
Similar projects recently burned down in Dorchester and Waltham, prompting some Boston-area cities and towns to launch extra inspections and enforce tighter fire-safety protocols. It was not immediately clear if Weymouth had taken such steps, and town fire and building inspectors did not return messages.
Mid-rise wood-frame projects have become popular in the Boston area because they allow developers to pack more apartments on relatively small sites, at costs significantly lower than concrete or steel.
Pulte, one of the nation’s largest homebuilders, followed its own fire-safety protocols at the project, part of a four-building complex in the giant Union Point complex known as Woodstone Crossing, said vice president Geoffrey Rendall.
“We follow all the life-safety codes, all the building codes. We have our own inspectors, and the city inspectors come through,” he said. “We try to stay up to snuff.”
They did not, however, have onsite security after-hours, a practice some experts consider a key element of fire-safety protocol, given that many fires start at night. And construction fencing around the building — which was set to open next month — was taken down last week so landscaping could begin, though the building was fully locked at the end of the day Wednesday, Rendall said.
The building was set to open in about a month, Rendall said, and 42 of its 50 condos had already been sold. Two of its four stories were completed, with work winding down on the lower two. But the sprinkler systems were not yet activated.
The company will determine how to handle people who already have contracts. According to its online posting for the development, asking prices range from $299,995 to $396,995.
“We will have to rebuild from scratch,” Rendall said.
Dozens of similar mid-rise, wood-frame buildings are under construction around Greater Boston as developers push to meet demand for housing here. Once they’re occupied, with safety systems up and running, fire experts say, the buildings are generally safe. But during construction, they’re basically a pile of wood, and can burn fast.
“You could have a spark smoldering in a corner,” said Brian Cooper, managing director of construction at insurance brokerage Arthur J. Gallagher & Co. “If it’s windy, and there’s no fire suppression, they go up like a box of matches.”
That’s what happened in late June at the Treadmark building in the Ashmont section of Dorchester, where Boston officials said an exhaust vent overheated, starting a huge blaze. It happened again a few weeks later at a four-building complex under construction in Waltham, which the state fire marshal is investigating as arson.
No one was seriously hurt in either fire, or in Thursday’s. But the first two episodes prompted state officials to review code enforcement and fire-safety rules, especially during construction. A group has met several times to design new training for local fire and building inspectors, said Jennifer Mieth, a spokeswoman for the Department of Fire Services, though no timeline has been set for rolling it out.
Better enforcement of rules already on the books should help, said Allen Fraser, a senior building code specialist at the National Fire Protection Association, a Quincy-based group that writes fire-safety standards nationally.
“The horror stories we are hearing are not about codes and standards,” he said. “They are, 99 percent of the time, about a lack of code enforcement.”
NFPA standards, for instance, require building owners to put someone in charge of fire prevention at a building site, and to address key safety measures such as debris removal, security, and quick communication when a fire does start. Those standards also allow municipalities to require overnight security, though most here do not.
Fraser acknowledged the procedures can be pricey. An overnight guard, cameras, fencing, and lighting might cost $300,000, he said. But that’s far less than the millions of dollars lost in a big fire.
Jay Doherty, CEO of Boston-based housing developer Cabot, Cabot & Forbes, said he expects to see more builders using flame-retardant wood, enhancing security, and monitoring of their sites and perhaps installing — and turning on — sprinklers at earlier stages of construction.
“This has not really been a problem until now,” he said. “But we can definitely improve on fire prevention and protection during construction.”
At the Union Point development, John O’Brien, who lives in a building next to the one that burned, said he watched the fire from his balcony Thursday morning, and it looked like an “inferno.”
“The whole roof was on fire,” he said. “It was pretty intense.”
O’Brien just moved to his own newly built building in December, and said he feels for his would-be future neighbors.
“To see a beautiful building so close to being finished,” he said. “It’s really a shame.”John R. Ellement of the Globe staff contributed to this report. Tim Logan can be reached at email@example.com. Follow him on Twitter @bytimlogan. Kay Lazar can be reached at firstname.lastname@example.org. Follow her on Twitter @globekaylazar.