Arson investigators say the fire that ripped through a Rockland County yeshiva yesterday has been deemed suspicious.

The fire sparked at around 11 a.m. Thursday at a building on East Funston Avenue in Spring Valley. More than 80 firefighters from five departments battled the blaze.

Investigators say it appears the flames broke out on the building's back porch.

An attic-turned-dormitory room where students slept was completely charred by the flames. Dozens of students were downstairs in classes at the time.

Authorities say the fire has been indicative of a larger problem: illegally converted buildings. County Emergency Coordinator Gorden Wren says the building, which had been previously cited for violations, was converted illegally and was unsafe for those who occupied it. "You can't just take a one-family house and make it into a dorm," Wren said.

Investigators say there's no decision on whether a summons will be issued for the illegal conversion.

The cause of the fire is unclear.