Britain's historic farm buildings are under threat from disuse, dereliction and "horror" conversions, English Heritage is warning.
Some private owners need support to carry out repairs
In a joint report with the Countryside Agency, the body says there is pressure on buildings such as barns, hop kilns, dovecotes and stables.
The report found 7.4% of listed farm buildings were in a severe state.
It would take £30m to repair these buildings and many more are in danger, the Heritage Counts report said.
Simon Thurley, chief executive of English Heritage, said: "Because they are falling out of use, they are vanishing fast.
"We are talking about thousands of barns, wagon sheds, byres, dovecotes, outhouses, stables and oast houses - these buildings face disuse and dereliction.
"Almost as bad is that some of them are being converted in such a way that is fundamentally unsympathetic to the buildings and very unsympathetic to the countryside itself.
"Almost a third of listed working farm buildings have already been converted, mainly to residential use, and this can do a lot of damage if it is not done with care and attention."
Dr Thurley said he was aware of some "horror" barn conversions which were causing the "suburbanisation of the countryside".
The report found that farm buildings made up the biggest category on council "buildings at risk" registers.
And at least 10% of farmers had historic buildings that needed repairs.
A survey in Hertfordshire suggested 36% of traditional timber agricultural buildings from 22 parishes have been lost or are in danger of being lost because of dereliction or conversion.
The report said this meant by 2020 every such building in the county will either have been converted, demolished or fallen derelict.
David Fursdon, president of the Country Land and Business Association, said it was important that private owners were supported in their conservation work.