They Built a Basement Over WHAT?! You Won’t Believe What We Found

🕵️‍♂️The Inspection Insider

The Inside Scoop for Buyers, Sellers, and Realtors

This Week's Inspector Spotlight: A leaking water tank led me to one of the wildest discoveries of my inspection career—a full-size swimming pool hidden beneath the basement floor.

When I noticed the hot water tank was leaking, I expected to find the usual puddle. But the floor was bone dry. The tank kept draining, yet the water was nowhere to be found. That’s when I realized—it was going somewhere. What I eventually found under the basement floor was one of the strangest things I’ve ever seen.

Not a routine inspection
This was a routine inspection on a tidy older home in a quiet neighborhood. The basement was finished, clean, and a bit dated—think 1980s paneling and a hint of musty carpet. The homeowners were downsizing, and the realtor said, “Everything’s in great shape—except maybe the water heater. It might be leaking.”

Understatement of the year.

The problem was more than the leak
I headed down to the basement utility area expecting to spot some surface rust or a little drip from the valve. Instead, the tank was slowly, steadily emptying—like it was being siphoned. But the floor was completely dry. No staining. No wet carpet. No water pooling under the tank. Nothing.

The tank wasn’t just leaking—it was losing gallons of water, and none of it was showing up. That’s when I knew something was very wrong.

The discovery
At first, I assumed a drain line had been rigged up—maybe a DIY fix to channel leaks into a floor drain. But there was no visible piping. I tapped around the base of the platform the tank sat on. Hollow. Suspiciously hollow.

A little poking around the surrounding basement revealed a section of floor that was, well… not really a floor. More like a thin wooden subfloor built on top of something deeper.

After checking for floor access panels I found one and pried it up. What I saw underneath stopped me cold.

It was a full size swimming pool!

Lesson Learned
This one was a textbook case of why you never assume the finished basement floor is just concrete under carpet. Always check for hidden structures, raised platforms, or signs of soft flooring in unusual places.

The buyers were stunned.

The sellers? They claimed not to know it was there—though given the custom access panels, that was a little hard to believe.

But then I was talking to the neighbor outside they told me that the original owner had the pool done when the house was built but had it floored over shortly after. They didn’t know why and the house had sold 3-4 times since then.

Had this not been discovered, the entire basement could have become a moldy, structural disaster zone. Not to mention the safety risk of a collapsing floor over a literal underground pool.

If you’re buying a house with a “converted or finished basement,” ask these three questions:

And if you notice a leaking appliance—but no puddle—and no floor drain, don’t assume it’s a minor issue. Start asking where that water is going. It might be going down… a lot farther than you think.

Just 15 feet from the back door, I spotted something that could’ve turned a family move-in into a medical emergency—a massive black wasp nest hidden in plain sight. With small kids and a dog in the picture, this one was a close call.

Ron Henderson, CMI
Certified Master Inspector

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