Wood Subfloor Problems

There are three major types of wood subfloors usually used in houses.

  • 5/8″ or 3/4″ CDX tongue and groove Plywood panels nailed to floor joists
  • Plank Subfloor (usually 3/4 inch thick x 4 – 8 inch wide pine) is found in older homes.
  • OSB (Oriented Strand Board) tongue and groove Subfloor – solid sheets nailed and glued to floor joists

Many problems with hardwood floors can be traced to the wood subfloor. Installed correctly, all three of the materials listed above will provide a dependable support for hardwood flooring and other types of covering, such as laminates, vinyl, carpeting and even ceramic tile. A moisture-free environment, correct design, and correct installation, however, are vital for a good floor. Here a few of the more common wood subfloor problems seen in homes:


This is a condition where the edges of the floorboards are raised up, creating a “cup” in the middle. Cupping is caused by varying levels of humidity in the floorboards. For example, a floor has absorbed humidity after it’s installation, making the boards expand.

One reason for this is a too much wood subfloor humidity. The undersides of the floor planks will then absorb a greater amount of moisture than the top surface, which causes top and bottom to expand to different amounts and then cup.

Creaking, Popping noises

Everone knows what this is. Over time, people living in a house will become used to it, but if you’ve just moved in to an older home, this can be a big problem. Wood subfloors can be the cause of it a number of ways.

Structure not being strong enough; if a subfloor is not firmly fastened to the underlying joists with floor screws, there will be space left between the joists and subfloor.

Wrong subfloor material for nailed installations. Particleboard is not a suitable material; you must use plywood or OSB panels.

Creaking can also be the fault of an improper subfloor thickness. Recommended thickness for plywood or OSB subfloor panels is ¾ inch for joists spaced 19″ or less apart center on center. Anything thinner can make the floor creak when it bends under the weight of foot traffic. Wider joist spans can also have the same effect.


Does you floor look wavy and slanted in spots? Your sub floor could be warped and loose. Also, the floor joists might be warped or even split. Supporting pillars and columns or walls could have settled, over time, or the perimeter foundation has settled unevenly..

Floor Sinking when Walked On

Is the floor spongy and springy in spots? Your subfloor may be improperly installed, not strong enough, or rotted from moisture. You’ll need to have a look at it, either from below if it is a main floor and you have a basement, or from above, by removing some of the floor covering in the suspect area.

Slanting floors

Not really a subfloor problem per se, usually is due to house and/or foundation settling problems. Cure involves removing subfloor and adding joists to level, then installing new subfloor.