Timber floorboards cupping


Cupping occurs when boards are drier on one side than the other, resulting in uneven shrinkage/swelling. Cupping may be due to boards swelling if the moisture levels of internal or subfloor spaces are higher than the moisture content of the boards.


  • if the floorboards were installed recently, contact the installer

  • minor cupping, such as that from seasonal changes in the atmospheric moisture, may correct itself over time

  • reduce excess moisture in the air inside the house by not drying clothes inside, not using unflued gas heaters, and by opening windows wide for at least 10 minutes every day. A rangehood should be installed above the cooktop and should vent the steam outside, and a bathroom exhaust fan should similarly vent bathroom steam outside

  • check that the subfloor space, if there is one, is not unduly wet. Make sure there is not less than 3500 mm² of clear open subfloor venting (grilles or gaps between baseboards) for every 1 m² of floor area. It can also help to lay 0.25 mm thick polythene to cover the ground under the house, lapped a minimum 75 mm, preferably taped, and butted to foundation walls and piles. The ground should be shaped so no water accumulates on the polythene. Weigh down the sheets with bricks or concrete

  • never clean timber floors with a steam mop or with very hot water or floods of water

  • if the cupping results in an unacceptable appearance, consult an experienced floor resurfacing company for advice

  • some solid wood flooring available today is produced with grooves in the back that are designed to reduce the risk of cupping. Engineered flooring is also available with a solid wood top layer and a core or backing or cross-layered ply or other material that also reduces the risk of cupping