What they did: Orren Pickell Designers & Builders dug a foundation and basement for the addition, then took down part of the wall between the old and new below-grade spaces. The new basement level added 915 square feet of living area and solved the moisture problem with perimeter drains and sump pumps. The space holds a projection screen TV and pool table under a 9-foot ceiling. "When those Chicago Bears are on—holy cow—the whole family's here," Cathy says.
Toughest part: Shoring up the house after removing most of the basement's back wall.
Favorite finishing touch: The home theater's hidden wiring.
Timetable: The whole-house renovation took 10 months.
Final budget: About $150,000, including finishing the existing lower level and adding a bathroom.