Home additions are typically the most expensive home renovation projects because they require not only renovation services but actual construction services like laying foundations and constructing load bearing walls.
Building an Addition costs in New York vs. National Average
Depending upon the type of space you are creating, you can recoup more of the cost by focusing on adding family rooms and bedrooms rather than sunrooms.
Also, your location plays a big factor - in NYC for example, you can recoup between 5% and 20% more on an addition compared to the same projects across the rest of the country.
Data courtesy of Hanley Wood.