Half of the people who rent from private landlords in Cornwall are living in sub-standard properties, the council has said.
A survey of the private sector housing stock revealed cold and damp homes and tripping hazards.
The report also claimed it would cost about £637m to get privately-rented houses up to scratch.
The survey comes as the housing charity Shelter is calling on the government to clamp down on rogue landlords.
Maureen Brown has lived in a rented house in St Austell, mid Cornwall, for 18 years.
'I panic now'
She said: "The roof is leaking, it's asbestos. The bathroom window could fall out on anyone underneath. The kitchen sink is leaking.
"I am now diagnosed with Alzheimer's. I feel that if I move now from an area I know, it's going to get worse for me. I panic now."
Cornwall Council said it had successfully prosecuted her London-based landlady, but so far no improvements have been made.
Ruth Clarke, from the Cornwall Residential Landlords Association, said: "There are bad landlords out there. One of the aims of our association is to educate landlords so that they do know their responsibilities."
Housing Minister Grant Shapps said a balance needed to be struck between landlords and tenants rights and responsibilities.
It said current legislation delivered that balance but said the situation was under review in the medium term.