How far off property lydo I need to build an addition to my house

How far you must be from a property line depends on the specific property location. You will very likely need a permit before building. There could be covenant restrictions in your specific housing development that restrict building in addition to those imposed by the city, etc. A good place to start may be your local city planning division's website. Below is a link to the website for the City of Omaha's planning department website and frequently asked questions. https://permits.cityofomaha.org/frequently-asked-questions