Types

• Hardwood floors normally expand and contract due to seasonal humidity. Gaps no bigger than the thickness of a dime between planks are completely normal. Buckling and cupping are fairly common types of warping as well but are a more serious type of warping than normal expansion and contraction. Buckled floors have come apart from the subfloor while cupped floors develop a "washboard" type of warp with planks rising up at the edges and sinking down in the center. Sagging floors that slope downward in the middle present the most detrimental type of warp, which is a thankfully rare type of warp.
  
  

Causes

• Natural humidity causes normal shrinking and expanding. As wood planks absorb moisture, they expand. The planks naturally shrink when they dry out. Likewise, moisture stands as the most common culprit for other types of hardwood floor warping. Moisture imbalance causes cupped floors; the wood is too wet near the bottom of the plank and too dry near the top. An excess of moisture on the surface of the floor or on the subfloor causes sagging floors.
  
  

Prevention

• Home humidity controls go a long way in preventing normal and abnormal warps in hardwood. Humidifiers help along dried out floors during the winter months while dehumidifiers help remove excess moisture caused by humid weather, leaks, spills or other factors. Maintaining your hardwood floor's finish also helps lock out harmful moisture that can lead to warping. Clean your floor with a dust mop or vacuum, but avoid damp mopping to prevent warping.
  
  

Repair

• Small gaps due to expansion and contraction generally correct themselves over time. Fix leaks immediately to ward off warping, and use fans to speed up the drying process. Buckling calls for professional reattachment of the wood to the subfloor while cupped floors will need to be sanded flat and refinished. Both cupping and sagging require stabilization of the home's moisture balance; these serious types of warping need professional care.