Causes: Dryness. The loss of moisture results in the most frequent reason for shrinkage of individual pieces and cracks. In other cases, when a floor has experienced water damage or high humidity over a length of time the edges of the wood can crush, and subsequent drying and shrinkage can present larger than normal cracks. Most cracks are seasonal – they show in dry months, or the cold season when heating is required, and close up during humid periods. This type of separation and closing is considered NORMAL. In solid 2 1/4” oak floors dry cracks may be the width of a dimes’ thickness (1/32”). Wider boards will have wider cracks. Cures: Add moisture to the air space during dry periods (see your manufactures warranty for humidity ranges) or live with the cracks.