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Why are my floors cupping?


Hardwood flooring is renowned for its warmth and elegance, making it a popular choice for many homeowners. However, hardwood floors are susceptible to a phenomenon known as "cupping," which can drastically impact their appearance and functionality. For professionals engaged in designing, building, and maintaining homes, educating clients about cupping in hardwood floors and implementing best practices from installation to ongoing maintenance are crucial steps in preventing this common problem and safeguarding the enduring appeal of hardwood floors.

What is Cupping?

Cupping is characterized by the edges of hardwood planks rising higher than the center, resulting in a concave or "cupped" shape across the width of the plank. This uneven appearance not only diminishes the aesthetic appeal of the floors but can also lead to further damage if left unattended.


Some Common (and Uncommon) Causes of Hardwood Floor Cupping

Moisture Imbalance

The primary cause of cupping is a moisture imbalance within the wood. Hardwood, being a hygroscopic material, naturally absorbs and releases moisture from the environment. When the bottom of the wood contains more moisture than the top, the sides of the board expand more than the middle, leading to cupping.

Sources of Moisture

  1. Humidity Fluctuations: Excessive humidity or dryness in the home can result in floor cupping. Maintaining indoor relative humidity levels between 35% and 55% is essential to prevent moisture imbalance.

  2. Spills and Leaks: Unaddressed spills and leaks from appliances or plumbing can seep into the floorboards, contributing to moisture imbalance.

  3. Subfloor Moisture: Moisture from beneath the flooring, especially in homes without proper moisture barriers, can lead to cupping.

  4. Climatic Changes: Seasonal shifts can cause fluctuating moisture levels, leading to wood expansion and contraction.

Improper Installation

Inadequate acclimation of hardwood floors to their environment before installation, or insufficient spacing for expansion and contraction, can lead to cupping.


Inadequate Finish

An uneven or inadequate finish on the wood can also contribute to cupping, allowing moisture to penetrate more easily.


Addressing and Preventing Cupping

Balancing Moisture Levels

The most effective way to prevent cupping is to identify and neutralize the source of moisture. This may involve:


  • Using dehumidifiers or humidifiers to balance indoor air moisture.

  • Promptly repairing leaks and addressing spills.

  • Ensuring there's an adequate moisture barrier between the subfloor and the hardwood.

Proper Installation

Allowing wood to acclimate to the installation environment for the recommended period and ensuring appropriate gaps for expansion and contraction during installation are crucial steps.


Regular Maintenance

Immediate cleaning of spills and prevention of water standing on hardwood floors are key maintenance practices.


Professional Inspection and Repair

For most cases of cupping, professional assessment - preferably by an NWFA Certified Professional -, sanding, or even board replacement may be necessary.


Understanding the causes and remedies for cupping in hardwood floors is essential for maintaining their beauty and functionality. By controlling indoor humidity, ensuring proper installation, and consistently caring for your floors, you can effectively prevent and address cupping issues, preserving the allure of hardwood floors for years to come.




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