Flames burst through the roof of the terrace house in Bridge Street South, Smethwick forcing next door neighbours to be evacuated.
West Midlands Fire Service said the house had been “completely destroyed” as the investigation continued today.
Officials also hit out at those behind the drugs den for putting neighbours and firefighters at risk by the blaze.
The fire started at about 2.30am this morning – it was confirmed no-one was injured.
Thirty firefighters had worked to stop the flames spreading to the neighbouring homes by daybreak.
Firefighters used hydraulic platform to reach the blaze from above.
The road outside the house was blocked off by the fire crews during the operation as bystanders watched on nearby.
At first light the severity of the blaze became clear as exposed roof beams could be seen where flames burst through.
It came after a suspected modern slavery victim died after being locked inside a cannabis factory when it caught fire in a Brierley Hill factory unit.
A West Midlands Fire Service spokesman said: “We’ve responded to a severe fire in a Smethwick house being used to grow cannabis – putting neighbours and our crews in danger.
“Properties either side had to be evacuated.”