A sunroom costs $100 to $350 per square foot on average. A 3-season room costs $8,000 to $50,000 to build, and a 4-season room costs $20,000 to $80,000 to add. A sun porch or prefa…

Most sunroom additions cost between $8,000 and $80,000. The average is just above $30,000. Expect to pay around $25 per square foot for uninsulated spaces and up to $300 per square…