Bathrooms are small rooms with an outsized capacity for expensive mistakes. Between plumbing, electrical, and constant moisture exposure, a renovation that goes wrong doesn’t just look bad, it can cause structural damage that shows up months or years later.
The most common and costly error is inadequate waterproofing behind tile. Cutting corners on a proper waterproof membrane in a shower stall might save a day of labor, but water that gets behind the tile and into wall framing can lead to mold and rot that isn’t discovered until the drywall on the other side starts to bubble.
Ventilation is the second major oversight. A bathroom fan that’s undersized for the room, or one that vents into the attic instead of outside, traps humidity that slowly damages paint, drywall, and even roof sheathing. Fans should be sized to the room’s square footage and always vented through the roof or an exterior wall.
Homeowners also frequently underestimate how disruptive plumbing relocation can be. Moving a toilet or shower drain even a few feet can mean opening up a subfloor, and on a second story, cutting into the ceiling below. It’s rarely impossible, but it’s almost always more expensive than keeping fixtures near their existing drain lines.
Finally, skipping a permit on a renovation that changes plumbing or electrical is a mistake that surfaces at the worst possible time: during a home sale. Unpermitted work can complicate a buyer’s financing or insurance and may need to be opened back up for inspection, undoing finished tile and drywall in the process.