Photo by Brock Builders

The cost of a home addition varies widely depending on the type of addition you are building, its size, how it connects with the rest of the house, whether it is one-story or two, and the type of foundation it sits on. There is also great variation depending upon location (part of the country).

In 2009, the cost would range from $38,000 for a midrange bathroom addition to $150,000 for a two-story addition. These figures are based on national averages for midrange additions. Costs will vary by location, materials used and contractor chosen.

The best way to get a closer estimate of the cost of an addition would be to try to think through some of the major details of the type of addition you would want to build. Think about the factors listed here: size, type of foundation (slab on grade, full foundation, post supports), how it connects to the rest of the house (how much work will need to be done to the existing house to make a connection?), one story or two story, how the space will be used (kitchen, bathroom, family room), quality of materials, and quality of workmanship expected. Input this information into an online calculator and get a cost estimate that should be accurate to within 20-35% of the actual cost.

One of the benefits of this kind of online calculator is that you can try different combinations of information and see how each of your decisions can be expected to affect the total cost of your project.  Another alternative is to take the information you have gathered to a local contractor and ask for a preliminary cost estimate.