The average cost to build a home addition or add a room is $48,000, with most homeowners spending between $22,500 and $74,000. A room addition costs from $90 to $210 per square foot depending on the room size, materials, labor, location, and if your building-up or out. Adding a room provides a return on investment (ROI) of over 50%.

As a do-it-yourself project, adding new floor space for a family room requires a wide range of high-level handyman skills and runs about $25-$50 a square foot, depending on complexity and materials, or about $10,000-$20,000 for a 16x25-foot room (400 square feet). A Michigan homeowner [ 1] spent less than $10,000 for a 20x14-foot family room.