how much does it cost to build an extension to my house
NEXT STEP. Find out how much your project will cost. Provide a few details about your project and receive competitive quotes from local pros. The average national cost of adding a room or building an addition is $40,960, with most homeowners spending between $21,711 and $63,014.This data is based on actual project costs as reported by HomeAdvisor members.he average national cost of adding a room or building an addition is $40,960, with most homeowners spending between $21,711 and $63,014.