More than a dozen privately provided social homes did not meet regulatory standards in Cornwall earlier this year, figures show.
A housing charity has said there is "no excuse" for poor quality social housing.
Regulations stipulate every social home in the UK must meet the Decent Homes Standard, which means it must not need major repairs, and have relatively modern facilities and solid insulation, among other regulations.
But figures from the Regulator of Social Housing show private social housing providers in Cornwall were aware of 16 homes which did not meet these requirements as of March.
These were a part of 1,271 homes not up to standard across the South West.
Data from the organisation shows 42,000 private social homes across England did not meet the standard in the year to March, with half a million buildings inspected.
Of the unfit properties, 37,500 were brought up to standard, while 1,800 were sold or demolished.
A further 5,200 buildings were excluded from having to meet the requirements, for reasons such as tenants not wanting improvement works to go ahead.
Combined with existing figures on homes not meeting the DHS, this means more than 13,000 homes across the country were not up to scratch as of March.
The Social Housing Action Campaign said there is "no excuse for such poor standards" of social housing.
A spokesperson said they were not confident of improvements being made while the Government is focused on delivering new homes, meaning "standards are far too often sacrificed".
They continued: "As well as the misery and suffering that people have to endure when they are in substandard homes, this also has a cost to the economy and the public purse" – with poor housing sometimes contributing to health issues.
The figures show private providers only surveyed around 20% of stock over the course of the year – meaning the true number of sub-standard homes is likely much higher.
A spokesperson for the Regulator of Social Housing said all social landlords have a duty to provide safe, decent places to live for tenants, and should put things right when they do not.
They added a new remit to proactively inspect landlords should drive long-term improvements, and are "working intensively" with landlords that have failed to meet standards.
"RSH data shows that housing associations are spending record amounts on repairs, including on fire safety, damp and mould and other issues. We will continue to monitor progress closely,” they added.
In total, there were 2.9 million private social homes in England as of March – 25,700 of them in Cornwall.
Alistair Smyth, director of research and policy at the National Housing Federation, said everybody deserves a "good quality, safe and affordable" home.
"Government figures show that over 90% of housing association homes meet the Decent Homes Standard, more than any other types of home including local authority, private rent, and owner-occupied homes," he continued.
He said the sector had made good progress over the past two decades, halving the number of homes that do not meet the DHS – but warned more work is needed, and urged for more Government funding for the sector.
A spokesperson for the Ministry of Housing, Communities and Local Government said they are taking action to make sure homes are "decent and safe".
In October the Government confirmed it was looking to extend the Decent Home Standards to private rentals.