Is it not permissible to construct restrooms and sewage pipes above the mosque, in order to prevent impurities from leaking into it, or does that not invalidate the old fatwa that permits building above the mosque?

Building and residing above a mosque is permissible according to the preponderant opinion of jurists, and there is no harm in it due to the generality of the Sharia (definition) evidences indicating the legality of developing mosques and performing prayers therein, and because the objective is achieved without harm. The ground floor takes the ruling of a mosque if its owner dedicates it for that purpose. Although a standalone building is preferable, given the high cost of land and the needs of Muslims, there is no harm in building above a mosque, with the precaution of carefully considering the locations of plumbing to avoid water leakage into the mosque.