A fire broke out early Friday at a Cotati duplex that was under renovation, destroying the building.

The blaze appeared to have started in an attic around 4 a.m. and quickly spread to the rest of the unoccupied duplex on East School Street, Rancho Adobe Fire Battalion Chief Mike Weihman said. When firefighters arrived, part of the roof already had collapsed. Multiple drivers called 911 after seeing the fire from Highway 101, he said.

“The reports to 911 came from people on the highway who thought it was a wildfire,” Weihman said. “The glow reflected over the trees. They couldn’t tell what was burning.”

Rohnert Park firefighters were the first to arrive, Weihman said. Cal Fire, Petaluma and Gold Ridge fire departments also responded to the blaze, which caused about $200,000 in damage, he said.

The fire spared another unoccupied duplex and single rental unit on the property, which butts up against Highway 101.

The cause of the fire remains under investigation.

RISING RENTS

The average rent in Santa Rosa has increased 37 percent in four years, according to RealFacts. Here’s a look at how the average rent for a two-bedroom apartment in the city has increased since 2011:

2011: $1,180

2012: $1,238

2013: $1,349

2014: $1,517

2015: $1,640

BY THE NUMBERS

13,386*: Total number of units rent control affects

$11.4 million: Estimated savings to renters by capping rent at CPI

$4.4 million: Estimated drop in business income: $4.4 million

$171,600: Estimated drop in property taxes: $171,600

*City of Santa Rosa estimate; Source: Rob Eyler, PhD.

STUDY SESSION

The City Council will explore the issue 2 p.m. Tuesday, Santa Rosa City Hall