A man was taken to hospital with injuries after the fire at Chesterfield Road, North Wingfield,at 3.20pm on Sunday, January 23.
The busy road was closed for several hours while fire crews from Clay Cross, Chesterfield and Alfreton, joined other emergency crews in tackling the incident.
A fire service spokesperson said the investigation was now underway.
A Derbyshire police spokesperson added: “One man was taken to hospital suffering minor injuries and has since been discharged.
“An investigation into the fire is ongoing with Derbyshire Fire and Rescue Service.
“If anyone has any information which they think could help with our enquiries, please contact us on the non-emergency details below, quoting reference 22*44012.”
Facebook – send a private message to /DerbyshireConstabulary
Twitter – direct message @DerPolContact
Website – complete the online contact form www.derbyshire.police.uk/ContactUs.
Phone – call 101.