If the buildings are damaged by an insured event covered by your policy....
Vaughan,
If that building was yours, you would not be covered.
The sudden discovery of "concrete cancer" does not constitute an 'insured event' in the eyes of the insurance company's solicitor who wrote the policy.
They would deem that to be a lack of maintenance over many years and/or decades.
You'd get nothing for the building, and therefore would also not be covered for loss of rent.
Paying your premiums and "having insurance" vs actually getting paid out by the insurance company is worlds apart. So far apart in fact, that massive insurance industries have sprung up all over the world to feed off the largesse. Warren Buffett and Berkshire Hathaway being a prime example.