To prevent your wood floors from failing (coming apart, pushing together, cracking or worse), you must first understand them...and they're more complicated than you'd think (like some people I know).
Come winter, Fall, Summer, Spring, wood floors behave differently. They also behave differently depending on where you live. Why?
Ever notice in the humid summer months your doors stick? This is because wood swells when it is humid. The same can be true for wood flooring. Both solid hardwoods and engineered hardwoods are susceptible.
The inverse is also true. Low humidity causes wood to shrink.
Any floor, solid or engineered will expand or contract with changes in humidity. The wider the flooring, the more expansion and contraction. This means any floor, solid or engineered may and often does experience seasonal gapping or cupping (see below for definitions of gapping and cupping). Seasonal gapping and minor seasonal cupping is normal. When purchasing a solid or engineered wood floor, your salesperson should tell this to you so you aren't caught unaware and think your floor has a problem after it's installed.
The amount of seasonal gapping/cupping depends on many factors. Species, thickness, wood grain orientation and width are the main factors.
Can you avoid seasonal gapping/cupping? No. In theory, you could if you maintain a completely stable relative humidity throughout the areas with the wood floors. In reality, this is impossible. Regardless of how tightly sealed your windows are, how effective your dehumidifier is, the humidity levels in your home will change.
35% - 55% is the recommended relative humidity range for wood floors
Good news. You can keep seasonal gapping/cupping to a minimum (and avoid ruining your floors) by keeping the relative humidity within the recommended range. 35% - 55% is the recommended range. A good flooring company won't even install a wood floor without checking moisture levels in your home and confirming the humidity is within range. (if they don't, insist they do) Once they're done with the install it is up to you to see that you provide your floor a nice, cozy environment.
Purchase a hygrometer. A good flooring company (like Bob Wagner's) will provide one when you purchase your floor. This allows you to monitor humidity levels and confirm that your home is ready for the install.
What happens if my home's humidity levels move out of the recommended range?
Cupping, crowning, gapping, oh, my! (and buckling)
Gapping: low humidity causes the wood planks to shrink and move away from each other causing a gap between planks.
Cupping: The edges of the floor planks are pulled up while the center remains lower. This happens when the top of the floor looses moisture but the bottom doesn't follow. It can also happen when the bottom of the planks absorb moisture from the subfloor and expand. Minor cupping is a normal result of seasonal relative humidity levels.
Crowning: The center of the floor planks are higher than the edges. This happens when the moisture on the top of the floor is higher than the bottom.
Buckling: Extreme expansion of the floor planks. Usually caused by a water leak or severe moisture conditions.
What if the humidity levels creep toward the edges of the recommended range?
If your home starts to close in on the 35% range, turn on your humidifier. Don't have one? Buy one. No doubt you've spent quite a bit of money on your floor. If you don't want it ruined, invest in a humidifier.
If your home starts to close in on the 55% range, turn on your (you can probably tell where I'm going with this) dehumidifier.
Where you live will determine whether you are likely to need one or the other or both. If you live in Houston, for example, chances are you'll never need a humidifier. Live in Phoenix and you'll probably never need a dehumidifier.
For those of us who live in more seasonally affected areas, having one of each (or a whole house unit) is wise.
Typical seasonal impact on wood floors looks something like this:
Spring: low to moderate humidity levels, not much seasonal gapping in the flooring
Summer: moderate to high humidity levels, floor joints will swell and press against each other
Fall: low to moderate humidity levels, not much seasonal gapping in the flooring
Winter: moderate to low humidity levels, most seasonal gappinng occurs in the winter
Is there a 'best' season to install my hardwood floor?
Spring and fall, when the humidity levels tend to be the most 'average' for the year.
humidity is EVERYTHING when it comes to wood floors.