WALTHAM (CBS) — Authorities said the flames that destroyed a Waltham apartment complex over the weekend were able to tear through the building so quickly because of its wood-frame construction.

Five buildings were reduced to charred debris in the fire, which began around 4 a.m. Sunday. The complex off Elm Street was still under construction, so nobody was inside at the time.

It took crews from over a dozen different communities nearly four hours just to get the stubborn flames under control.

Waltham Fire Chief Paul Ciccone said the complex was in line with all building codes–but said this was a case where the wood-frame construction didn’t do firefighters any favors.

“There’s not a lot we can do about it, but wood is always very disconcerting to us because wood burns,” he said. “When you have a complex of this size, which is primarily wood frame, wood stick construction, it’s a big concern. And when it’s in a spot like this, it’s very congested, it’s very hard to access. We see these go up, we keep an eye on them.”

Firefighters were still putting out hot spots Monday morning, more than 24 hours after the fire began.

“There’s still fire underneath there,” said Ciccone. “It will go out, or it will flare up, and if it flares up, then we’ll knock it down.”

Waltham firefighters still putting out hot spots 25 hrs after fire started at apartment comp on Elm. Look right above the hydrant @cbsboston pic.twitter.com/PZKYOtxtvx — Nick Giovanni (@NickGNews) July 24, 2017

Ciccone said Monday’s rain was helpful to crews putting out those hot spots. Earlier, he said it could take a few days to get heavy equipment in to move the debris and completely extinguish the blaze.

“You can see there are some concrete stairwells that are all standing, some metal staging,” said Chief Ciccone. “Right now those are all suspect so we will be taking those down at some point. A couple of them will come down today, and then we can proceed with the investigation.”

Waltham City Council Vice President Robert Logan pointed out the similarities between the Waltham fire and a blaze that tore through a complex in Dorchester a month ago, and asking the state to revisit construction laws.

Logan said both the Waltham and Dorchester complexes utilized an almost all-wood frame.

“I have never seen a steel frame construction go up that fast,” Logan said.

He says the state should revisit the 2009 decision to change building codes that allows wood frame construction to be built.

“We cannot get involved in how they building buildings. That has to be done at the state level,” Logan said.

“I intend to bring in a resolution to the Waltham City Council for what it’s worth, to ask our local delegation to bring something in at the state level to look at this issue and see if maybe we can get the state building code changed.”

The upscale complex was set to open later this year. All 260 units were completely destroyed.

The blaze forced the evacuation of about 150 people from nearby assisted living facilities.

The cause was not yet known, but the investigation cannot get underway until the remains of the buildings stop smoldering.

WBZ NewsRadio 1030’s Carl Stevens reports