How does moisture content affect my hardwood floors?

Hardwood flooring is a natural product and is affected by changes of humidity in your home.  Wood expands and contracts as humidity changes.  Installing hardwood in a home with uncontrolled climate may result in damage to the floor.  During winter months, wood releases some of its moisture due to lower humidity.  This can result in gaps appearing between planks as the wood shrinks.  This is normal and not a flaw in the materials.  Keeping the humidity to an acceptable level, as set b manufacturers' recommendations of between 35% to 60%, a good humidifying system decreases the amount of expansion and contraction (ie. less gapping).  During high levels of humidity, the wood will absorb moisture and swell.  As the boards expand, the increased pressure against each other may cause a noticeable cupping of the boards where the sides of the planks are higher tan the middle of the board.  Crowning may also occur if the boards unevenly absorb moisture.  This appears as the centre of the boards are higher by the edges.  Engineered woods, which use a veneer of wood over stable plywood or manufactured composite materials, are less likely to be affected by humidity.  This is especially important as the width of the plank increases.