The property on Cromford Road was destroyed by the fire which took hold last Tuesday evening.
Police say it is believed to have been caused by a large cannabis growing system in the premises. Several plants were found by the fire service during an investigation on Wednesday morning.
Investigating fire officer John Caulton said: "The fire started in a rear room on the ground floor and developed to the upper floor and the roof over a number of hours, leaving total devastation and causing the floors to collapse.
"It is difficult to say exactly what caused it but it was likely to be an electrical fault because there was so much equipment in there.
"There were five or six rooms dedicated to the growing of £100,000 worth of the
product.
"The room which the fire started in was so badly burnt that it was impossible to know what was contained in there prior to the fire."
Following the find a police enquiry led to officers conducting a search at a house on Nottingham Road in Derby where 600 plants, believed to be cannabis were
recovered.
Two men were arrested and later released on bail without charge.

This find follows other drugs hauls found during a major police operation to target people who grow cannabis and up to £100,00 worth of the drug has been recovered from 11 addresses in Derby, Amber Valley and one in Nottinghamshire.
Five men were arrested and bailed for offences including aiding and abetting the production of cannabis, abstracting
electricity and firearms offences.
Police are urging anyone who knows or suspects their neighbours are involved in the production of cannabis to contact them. All information will be treated in confidence and officers will make extensive inquiries before taking action.
Anyone who can help the police can ring direct on 0845 123 3333 or call crimestoppers on 0800 555 111.