User blog comment:B214/Season 3 confirmed!!!!!!/@comment-110.147.195.80-20150124231246/@comment-25032153-20150124232319

well it coud be the devils could have done it at night when Issei was working and they speed up the construction via magic so it was finished in one night and Issei just ingore it as he had all the women in ACA over and he was being pervert and doing a pervert stuff and just didnt realise because the couple of floors are the same as the original house.