The cost for an addition on a house can be estimated in several different ways. These are listed below, from the least to the most accurate.

Photo by H Gruber

1. Dollars per square foot. To get this estimate, the square footage of the area to be added is multiplied by a cost. For example, a master suite addition that is 300 square feet in area would cost $60,000 to add if a $200 per-square-foot-cost is used (300 x 200=60,000). This method is quick and easy, but does not take into account the quality of materials, the amount of DIY  labor or the type of room that will be added.

2. A modified cost-per-square-foot method adjusts for variables, including which rooms will make up the addition, the type of materials, quality of workmanship, and whether the work will be done by the homeowner. This is the the method used by the free cost calculators on this website.  Click here to use them.


3. The most accurate method for creating an estimate is also the most time consuming. A full set of detailed plans are needed, as well as a list of materials and careful labor estimates. Together these can be analyzed by an experienced builder to create a very accurate estimate.  Click here if you would like to use our free contractor referral service.

I have come to believe the only time you will REALLY know the cost for an addition on a house is AFTER the work has all been finished. But adding on to a home can be a great way to improve your quality of life so don’t be deterred, go ahead and move ahead.