Home Improvement Expert Danny Lipford

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How to Keep Wood Floors from Buckling and Cupping

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We recently had new siding put on our house, and now the wood flooring is starting to buckle. What could be the problem? – Lynn

Hi Lynn,

Usually problems with buckling or cupping in a wood floor are caused by excessive humidity inside or under your house. It’s possible that a nonpermeable housewrap was used behind your new siding, which is increasing the humidity level in your home; or that the siding covered up existing foundation vents under your home.

In either case, you should monitor the humidity level inside and under your home using a humidity gauge (hygrometer) to make sure both areas are under 60% relative humidity.

Solid wood flooring moves constantly as the humidity level changes – expanding when the humidity is high and contracting when the humidity is low. This problem is particularly pronounced during a hot, humid summer or cold, dry winter.

Reasons Wood Flooring Buckles or Cups

  • If the humidity level inside or under the house is much higher than the wood flooring was acclimatized to when it was installed, it can cause the boards to expand and buckle.
  • If the humidity level inside or under the house is much lower than the wood flooring was acclimatized to when it was installed, the flooring may shrink and leave gaps between the boards.
  • If the humidity level is much higher or lower inside your house compared to under it, it can lead to the boards cupping.

If the flooring cups down (the center of the width of each floor board on top is higher than the edges), the humidity inside your house is substantially higher than the humidity in the crawlspace or basement under it.

If the flooring cups up (in a “U” shape on top), the humidity in the crawlspace or basement is much higher than that inside your house.

How to Reduce Humidity Inside a House

  • Run a properly sized air conditioner during hot, humid weather.
  • Use bathroom vent fans (vented to the outside) during and for 10-15 minutes after showering or bathing.
  • Run a kitchen stove vent fan (vented to the outside) when cooking.
  • Make sure the clothes dryer vent is unobstructed and vents outside your house.
  • Consider installing a dehumidifier if the above suggestions are not enough to lower the humidity level under 60%.

How to Reduce Humidity Under a House

  • Make sure there isn’t any standing water in the crawlspace or basement under your house caused by plumbing leaks or drainage problems.
  • Be sure the ground slopes away from your house, and rainwater is diverted away from the foundation.
  • Seal the walls and floor of your basement with a waterproof sealer, or cover the ground in the crawlspace with thick (6-mil or more) plastic sheeting.
  • Make sure there is adequate ventilation in the crawlspace under your house (1 square-foot of vent space per 150 square feet of crawlspace).
  • If problems with high humidity in the crawlspace or basement under your house persist, consider closing up all vents and installing a dehumidifier under the house or conditioning the space under the house.

Good luck with your project,

Danny

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2 Comments on “How to Keep Wood Floors from Buckling and Cupping”

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  1. Official Comment:

    Ben Erickson Says:
    March 28th, 2011 at 1:28 pm

    Test of comment checkbox

  2. Dan Hayes Says:
    October 11th, 2014 at 9:01 pm

    Have new construction house on slab with engineered hard wood clued down. First round of flooring cupped. Floor replaced with same type flooring using special moisture resistant adhesive. Slab passed moisture reading required for gluing flooring. Second floor also failing with cupping over 65% of floor. Now scheduled for third round of flooring. Different type of engineered hard wood, same moisture resistant adhesive. Chance of success? No drainage issues with landscaping or lot. Should floor be floated with click lock flooring?

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