The flames broke out at the rental home attached to a main house on Crater Camp Drive in the small unincorporated community of Monte Nido
Three men in their early twenties were taken to the hospital with burns to their upper bodies, arms and faces.
Hazmat and narcotics teams looked for evidence of a drug lab at what's left of the house and found indications that the fire was sparked by butane.
Phil Ulloa, a county fire department supervising dispatcher, said the chemical is used to refine marijuana.
CNS contributed to this report.
