Warped floors after water damage: cupping, crowning and buckling

What to do when you first notice it

Find and stop the water first: check under the dishwasher and refrigerator, around toilets and tubs, and at the nearest exterior door. Pull up area rugs and move furniture off the affected boards so they can breathe. Run the air conditioning or a dehumidifier to bring indoor humidity down. Then have the boards and subfloor measured with a moisture meter before anyone sands, nails or replaces anything, because the readings decide what can be saved.

Cupping, crowning and buckling

Wood swells as it absorbs moisture and shrinks as it dries. In a floor, boards are packed edge to edge, so swelling has nowhere to go but up:

• Cupping: the edges of each board rise above the center. The bottom of the board is wetter than the top, so moisture is coming from below or water got under the floor.
• Crowning: the center of each board is higher than its edges. Often a floor that cupped was sanded flat while still wet, and when it dried the edges shrank down. Water sitting on top of the floor for a long time can also crown boards.
• Buckling: whole sections lift off the subfloor, sometimes several inches. This takes a lot of water, such as a flood or a long leak, and often pulls the nails or breaks the glue.

Common causes

• Leaks from fixtures and appliances: dishwashers, refrigerator ice maker lines, toilets, sinks and washing machines on upper floors.
• Burst or leaking supply pipes under the floor or in nearby walls.
• Water from outside: a doorway threshold, a leaking slider or water pooling against the foundation.
• Moisture from below: a damp crawl space under the house, or moisture rising through a concrete slab.
• Humidity: months of high indoor humidity, especially in a house left closed with the air conditioning off.
• Wet mopping or pet accidents repeated over time in the same spot.

Hardwood: dry first, decide later

Solid hardwood is more forgiving than it looks. Once the source is stopped, the floor is dried from both sides when possible: drying mats sealed to the surface draw moisture up through the boards, while air movers and dehumidifiers work on the room and, where it can be reached, the subfloor from below. Readings are taken in the boards and the subfloor until they match the dry parts of the house. Then the floor is given time, often a few weeks, to settle. Many cupped floors flatten enough to be lightly sanded and refinished. Boards that buckled, split or stayed badly distorted are removed and new boards woven in.

Laminate, engineered and vinyl plank

• Laminate has a fiberboard core that swells at the seams and stays swollen. Wet laminate is usually replaced, at least in the affected area.
• Engineered hardwood has a real wood veneer over a plywood or composite core. It handles moisture better than solid wood in some ways, but soaked layers can separate.
• Luxury vinyl plank does not absorb water itself, but water runs through the seams and sits on the subfloor underneath. Click-together planks are taken up so the subfloor can dry, and can often go back down.

The subfloor

Whatever the finished floor, the subfloor underneath decides whether a repair lasts. Oriented strand board swells at the edges when soaked and may not flatten again; plywood can separate between its layers. Before any new flooring goes down, the subfloor is measured dry, soft or swollen sections are cut out and replaced, and any mold on the subfloor or joists is dealt with.

Replacing and matching

When boards have to be replaced, they are woven into the existing floor rather than patched in a block. A whole room is often sanded and refinished afterward so the old and new boards match in color. If the same flooring runs through several connected rooms with no break, replacing only the damaged part can leave a visible difference, which is worth raising early with the insurer. Water damage repair covers how flooring is matched, and structural drying covers the drying itself.