Sefton Group sold the building last month
Building inspectors have lodged several complaints about the deteriorating state of the Castle Mona over the past five years.
The iconic hotel in Douglas, which closed in 2006, is a protected registered building.
It was bought from previous owner the Sefton Group earlier this month.
Now reports from more than a dozen assessments carried out on the site since 2012, published following a Freedom of Information request, show there have been concerns over water damage, rising damp and leaks throughout the site.
Roosting pigeons on the roof were claimed to be causing a 'health issue' - and planners found a number of alterations inside had 'reduced the historic interest' of the centuries-old interior.
Repairing the damage, according to planners, could be 'prohibitively expensive' for a future developer.
The identity of the Castle Mona's new owner has yet to be established.
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