Why is my hardwood floor cupping?
Cupping means the edges of each board sit higher than the center. It almost always means the bottom of the boards holds more moisture than the top. The moisture usually comes from below (a damp slab or crawlspace), from a leak, or from high indoor humidity.
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What usually causes it
- Moisture rising from a concrete slab or crawlspace
- A plumbing, appliance or HVAC leak
- High indoor humidity, common near the coast
- Wood installed before it acclimated, or a missing or failed vapor retarder
What you can check yourself
- Look for leaks around sinks, dishwashers, refrigerators and exterior doors
- Note whether it is worse in one area or season
- Don't sand a cupped floor yet: sanding before it dries can cause crowning later
What an independent inspection checks
- Moisture content of the flooring and the subfloor, mapped across the room
- Room temperature and relative humidity, and how they change by season
- Concrete slab moisture (ASTM F2170 in-situ RH) when the floor is over concrete
- Installation method and acclimation against NWFA and manufacturer guidelines
Who is responsible?
It depends on the moisture source. A site moisture problem usually isn't a product defect; an installation that skipped required moisture testing may be the installer's responsibility. A written report documents which applies.
Get your hardwood floor inspected
Tell us what you're seeing and we'll explain the next step. We cover every county in Southern California and only inspect. We don't sell or install flooring.