While costs vary based on several factors, CostHelper.com estimates a do-it-yourself second story addition costs between $70 and $150 per square foot in 2014. Hiring a contractor for the work increases the cost to the $100 to $500 per square foot range, depending on the complexity of the project.
Adding a second story is often a good option when the lot size is limited. In many cases, this saves the cost of adding a foundation. However, CostHelper.com estimates the addition to cost 20 percent more than adding at ground level. Pulling a building permit triggers the local authorities to re-evaluate the value of the property, which may increase the property taxes owed each year on top of the initial investment.