'Tis the season for cupped floors, and I have gotten many calls about them lately. It has been a hot, humid summer, and air conditioning has been running strong in much of the country. So lots of floors have been cupping.
The primary cause of cupped floors is wetter board bottoms than tops. Warm, humid summer air and air conditioning contribute to wet bottoms and dry tops. Warm, humid air adds moisture. Air conditioning removes it, but also affects the floor's temperature.
A flooring board on top of a wood subfloor or concrete slab is affected differently by the environment above and below the flooring. When you change the temperature of one surface, you affect the RH on the other surface. Affecting the RH, in turn, affects the wood moisture content and size.
Reports I see often say that the flooring is cupped because the bottom is wetter, but they don't provide any moisture measurements. How do you rule out the other causes of cupping without moisture measurements? Put away your non-invasive meters and get out your long, insulated pins and pound them through the flooring. You will make big holes, so be kind to the owners in picking your locations.
Once you verify a significant difference between top and bottom moisture content, what do you do? As an inspector, technically your job is done: You have determined the cause of the cupping. Addressing the situation is another story.
