Yukanari (床鳴り) – n – a creaking floor. Yukanari can be caused both by shoddy initial floor installation as well as simply by age, seismic activity, and settling. Ideally, if a structure is built to code, where the foundation and structure is built to withstand moderate seismic activity, and flooring is installed according to the specifications of the manufacturer, yukanari should not be a problem.
One of the most common causes of yukanari is insufficient and/or mis-application of glue. Nails and staples are common fasteners used to secure flooring, but a generous application of glue is often required in addition to these fasteners. There are 2 primary reasons for this: Non-level subfloors and stresses caused by moisture entering and leaving natural wooden flooring.
Both of these can place significant stress on a given flooring board (enough to loosen the hold of the fastener), both at the time of installation as well as after some time has passed (after it has dried out, for example).
– See my other page What Causes Squeaky Creaking Floors.