Dubai Municipality (DM) is the default building authority for mainland Dubai - any property that isn't inside a free zone (like JLT or a TECOM zone) or a master-developer community with its own NOC process (like Nakheel or Emaar). That covers classic villa neighbourhoods such as Jumeirah, Al Wasl, Al Safa and Umm Suqeim, plus mainland apartment and commercial areas like Deira and Al Quoz.
 

DM approval is required for structural changes, MEP rerouting, electrical load increases, extensions and any increase in built-up area (BUA), submitted through the Dubai Building Permit System (DBPS) by a DM-registered consultant. Purely cosmetic work - painting, fixture swaps, like-for-like flooring - generally doesn't need it.