Room addition costs mainly depend on the kind of room being installed. Bedroom: A 10-foot by 12-foot bedroom costs $9,600 to $24,000 to build or an average of $80 to $200 per square foot.

As more homeowners stay put longer, many are hitting a wall—literally. One in 4 say they need more space, according to one survey, with another quarter reporting they outgrew their home just two years ...