There really was a madwoman in tha ttic

Charlotte Bonte wasn't completely making up the story of the first Mrs Rochester. It seems she based the story on a house she visited

Charlotte visited Norton Conyers in 1839 and knew the story of the mansion's 'madwoman' - probably epileptic or pregnant with an illegitimate child - who had been kept locked in an attic 60 years earlier.
The real and fictional halls are, in Bronte's words, 'three storeys high, of proportions not vast, though considerable, a gentleman's manor house, not a nobleman's seat'. Both have battlements, a rookery, sunken fence and wide main oak staircase. But until this month, only Thornfield had a hidden flight of stairs from near Mr Rochester's grand bedroom to his wife's miserable prison.