Any place where Hamess (Hametz - leaven) was known to have been taken, must be checked. Not only that, but any place where there is reason to believe that Hamess might have been taken, must also be included in the Bediqah (search).
All the rooms of one's house, therefore, including the attic, must be checked since, occasionally people enter them with a piece of bread in their hands. Also included are storerooms where wines and other beverages are stored, because it is not uncommon for people to go there during their meal to get a drink. However, if it is known that no one enters these storerooms during their meal (or at any time) with bread or other leaven in their hands, they do not require checking.
It also goes without saying that if there are children in the house, all areas to which they have access, require checking.
(See Shulhan 'Arukh, 433: 3. Kaf Hahayim ibid, Oth 22-30, 35. M.B. ibid, 13-17.)
