Damage to the Regency Woods apartment complex from Saturday’s four-alarm fire has been estimated at $3 million, according to Renton Deputy Fire Chief Erik Wallgren.

Midweek, the fire investigation was continuing, including to determine its cause. The investigation is complicated by the size of the fire and the number of interviews investigators must do, Wallgren said.

Thirty-nine residents were displaced from their homes but nearly all found temporary housing immediately with friends or family.

No injuries were reported in the wind-whipped fire that was reported at 1:46 p.m.

At the peak approximately 140 fire personnel from Renton, Kent, Seattle, Bellevue and departments from as far as Snohomish and Pierce counties were on the scene. Off-duty firefighters backfilled Renton’s fire stations to ensure the entire city had fire coverage, Wallgren said.

Winds, estimated at 20 to 30 mph, were a “major contributing factor” in fighting the fire, Wallgren said. Such winds are unusual for this time of year, he said.

There was “significant potential” the winds could spread the fire to other apartment buildings at Regency Woods and apartment complexes in the area, he said. Embers ignited fires in dry grass and trees, including in the right of way that carries the BPA powerlines.

Renton’s brush truck and such trucks from other local agencies were used to fight the brush fires in remote areas where full-sized fire engines can’t go, he said, playing a “critical role” in fighting the fire. They are the size of a pickup truck and carry their own pumps.

Already, Wallgren said, there have been five or six brush fires along the BPA powerline.

Fire crews were called in Saturday night to watch for brush fires, he said. Firefighters were on the scene of the main fire on Sunday, too.

The Regency Woods fire is similar to two other major Renton fires in recent years, one in downtown Renton and one at an unfinished condominium project on Harrington Avenue in the Highlands, that required an “extraordinary amount of resources to control and mitigate,” he said.

The Regency Woods complex wasn’t equipped with sprinklers, which Wallgren said would have made a “significant difference” in the outcome of the fire.

“Statistically, sprinklers save buildings,” he said.

But sprinklers weren’t required when Regency Woods was built in 1968. Its 49 buildings underwent major remodeling starting in 2007 and completed in 2010, according to Greg Cerbana, a spokesman for Weidner Properties of Kirkland, which owns and manages the complex.

Because of the size of the buildings, sprinklers weren’t required, Cerbana said.

The fire destroyed a three-story, 12-unit building, which was then demolished, and heavily damaged two others. Sixteen of the 20 apartment units affected by the fire are a complete loss, Cerbana said. The fate of the other four remained to be seen as of mid-week, he said.

Residents were allowed inside one of the buildings, with an escort, to retrieve personal items, but that wasn’t the case for the other building, he said.

Some apartments are available at Regency Woods for displaced tenants, he said.

The American Red Cross was called in to help displaced residents, but it wasn’t necessary to open an emergency shelter because most residents found somewhere to stay, according to an American Red Cross spokesman.

“Right now, we’re actively helping five families navigate the process,” spokesman Colin Downey said Monday.