THE urge to downsize is not limited to empty nesters and retirees. It can hit anyone at any time. And sometimes it’s the family dog that helps you realize you have more space than you need.

This is how it was for Greg Kelly, a 50-year-old business appraiser in Raleigh, N.C., and his wife, Laura Herring, a 45-year-old pediatrician, who have two teenage sons, Troy and John. Earlier this year, they downsized from a house with more than 3,000 square feet to one that is half that size, cutting their property taxes in half and their aggravation even more.

Looking back on the unused space they once had, Mr. Kelly laughs. “It was a five-bedroom house, one bedroom used for a playroom, one for an office, with a separate dining room and a bathroom upstairs that literally we only used to wash the dog,” he says. “We had a dining room and a formal living room — that was where the dog lay on the couch, that was his room.”

So if the dog, a collie named Toby, was in the living room, where did the family hang out?

“The eat-in kitchen and the family room in the back of the house,” Mr. Kelly says. “If we looked at where we lived as a family, it was the back of the house. When I thought about it, I realized we never spent any time in the bedrooms, except to sleep. The boys did their homework in the kitchen. The house was a waste. My wife and I don’t pay to have houses cleaned, we’re just not wired that way, and it was killer to vacuum and clean a 3,200-square-foot house. It’s a breeze now. We were heating and cooling this huge house, it took a lot of physical and emotional energy to maintain it, and we were not living in that space.”