Why You Should Always Try the ‘Tennis Ball Test’ Before Buying a House

You’ve got a measuring tape, your phone is fully charged and you’re armed with a whole checklist of questions. You’re ready for a day’s worth of home tours, as you search for The One in this frenzied, “it was listed five hours ago but already has nine offers” market.

Well, you’re almost ready. Turns out, there’s one unexpected item to grab on your way out the door—and having it on hand could save you serious headaches down the road: a tennis ball.

Yes, that’s right. A tennis ball. Or bouncy ball. Or hell, if you’re feeling spunky, even a basketball. The ball itself doesn’t really matter; it’s what you do with it, which we’re calling The Tennis Ball Test.

Once you find a home you love, grab the ball and place it on the floor. “If it rolls to one side of the room, that’s a problem,” explains Christian Fuentes, broker and owner of RE/MAX Top Producers in Diamond Bar, CA.

It’s a sign that the flooring is uneven, which could range from sloppy retiling to even bigger problems with the foundation itself. Either way, it’s a red flag that’s worth exploring further.

“Sometimes, investors will just do cosmetics—patch cracks in the floor and paint over it, or tile over existing tile—if they’re looking to make a quick buck,” Fuentes says.

At first, you might be tempted to write it off (after all, homes are moving so fast right now, and no house is perfect, right?), but even if it’s just a case of the seller installing new floors on top of old ones, consider it a cue to proceed with caution: If they cut corners there, it’s likely they cut corners elsewhere while getting the home ready to sell. And if it’s an issue with the foundation, that’s cause for a larger conversation. Most homeowners spend about $4,513 on those repairs, though if you’ve got structural damage, you could spend more than $10,000, according to HomeAdvisor. (If you’re worried that’s the case, have your real estate agent ask the seller about any known foundation problems, and take a close look for other warning signs, like cracks in the walls and doors and windows that are misaligned.)

No matter what, if you decide to put an offer on the house, you should get an inspection, and if you suspect there are foundation issues, it could be worth hiring a foundation specialist to take a look at the place, Fuentes says. That way, you can get a sense of how much the project will cost you and either ask the seller to make repairs or negotiate down the cost of the home. (In today’s market, it’s more common to have the seller offer it “as is” and reduce the price.)

At this point, you might be saying, “why bother with the tennis ball? Isn’t it my inspector’s job to catch foundation issues?” True, but it’s ultimately on you to do your due diligence before buying a house, and if you’re already on the fence about a space, knowing it fails the Tennis Ball Test may help you move on to other homes, rather than spend $300 to $500 on an inspection (and lots of back and forth) on a house you ultimately walk away from.