avg cost to install a second floor in a house
1 Hiring a remodeling contractor to build a second floor addition can run $100-$300 a square foot for the typical addition (2-3 bedrooms and a bath plus a flight of stairs), but can go as high as $400-$500 per square foot depending on complexity, quality of materials and local labor rates.uilding a second floor (also called a second story) can added much-needed space, but costs at least 20 percent more than building the same square footage at ground level. However. if you don't have the land to build out it can make sense to go up. Typical costs: