The 60-year-old, who operates the business East Gippsland Home Projects, was convicted and fined more than $32,000, including costs, in the Bairnsdale Magistrates Court.
Johnstone pleaded guilty to 3 charges including carrying out domestic building work without the required registration and without the required domestic building insurance (DBI).
The court heard Johnstone quoted more than $84,000 to repair water damage in the Bairnsdale home which included replacing windows.
He then asked for a 50% deposit to enable the work to start when the maximum amount allowed is only 5%.
Johnstone's poor workmanship, which included unsealed windows and walls, left the home exposed to the elements and therefore unliveable.
The single mum had to separate from her children and dog to save on relocation costs while she paid another builder $11,000 to get it fixed.
In a victim impact statement, the homeowner said she suffered huge emotional distress, anxiety and panic attacks as a result of the ordeal and had to take out a second mortgage.
Magistrate Tim Walsh said the offences – in particular the lack of insurance – "cannot be understated and must be met with consequences and deterrence".
Consumers should always use a registered builder for jobs over $10,000 and ensure the builder has DBI for jobs over $16,000.
The BPC's CEO and Commissioner Anna Cronin said this case highlights the importance of hiring a registered building practitioner.
"Unregistered practitioners are a threat to safety and can leave consumers with no course of action when their work is seriously defective", she said.
You can check a practitioner's licence, registration or disciplinary and prosecution history at bpc.vic.gov.au/check .
The BPC acts within its legislative powers to protect consumers and improve confidence in the building industry.
