The new owners had had to turn out all the rooms which were full of rubbish.
had had : in which situation we have to use had had
Ganesh
This is the past perfect tense. The past perfect requires the use of ‘had’ plus the past participle of the main verb.
In the case, the main verb is ‘to have’, so the the past participle is ‘had’, and you end up with ‘had had’.
Compare to:
‘had run’
‘had sung’
‘had eaten’
‘had jumped’