Adding to an existing home is generally more expensive than remodeling because it involves constructing new walls, foundations, and roofs. Second-story additions particularly can drive up costs, especially if the original foundation needs upgrading to support the additional load. For additions, costs typically fall between $150 and $300 per square foot, with simpler one-story additions on the lower end and more complex second-story projects on the higher side. Custom or luxury additions might push costs to $300 - $475 per square foot.