how much do additions cost
1 Home addition cost estimates of $80 to $130 per square foot for a basic family room addition is common. 2  If the home addition includes a bathroom and/or a kitchen, the room addition costs can easily escalate to $200-250 per square foot.3  Quality and materials used are the other cost factors in a home addition.rimary factor, specifications of in the room addition plans. Examples: 1  Home addition cost estimates of $80 to $130 per square foot for a basic family room addition is common. 2  If the home addition includes a bathroom and/or a kitchen, the room addition costs can easily escalate to $200-250 per square foot.