Seasonal Floor Movement

May 30, 2014

Posted in macstaff

One very important thing to understand when choosing hardwood for your flooring is that wood is what is known as a “hydroscopic” material—it will absorb and release moisture in response to the moisture in its environment.  This means that, no matter the quality of your flooring or the skill with which it is installed, some seasonal expansion and shrinkage should be expected, and slight changes in the appearance of your floor will likely occur.  If your hardwood is properly installed, however, this movement will never compromise its structural integrity of your floor or significantly detract from its appearance.

A wide variety of factors can affect the movement of your floors.  At Macwoods, we are happy to discuss these factors with you to help you determine what kind of flooring and installation would be best for you and your home.


Jobsite conditions:   This is an especially important factor for floors being installed in brand new homes or homes being extensively renovated.  When a building has just been constructed, a great deal of moisture is present in materials like concrete, mortar, drywall, paint, etc.  With modern measures taken to conserve energy on jobsites, much of this moisture remains in the home for quite some time after the floors, walls, etc. are considered “dry”.  If hardwood is laid during this time, it will readily absorb this moisture as it evaporates into the air inside your home.  If this excess moisture is not accounted for during installation, or better, avoided by waiting to lay the hardwood, the floor will be left with unsightly gaps once the moisture has dissipated or may cup or warp as it absorbs moisture after installation.  Whenever possible, it is best to wait for the house to “dry out” before installing your floors.

Timing of installation:  Since the relative humidity in the air changes with the seasons, it is important to take into consideration how much moisture is in the air at the time of installation.  If it is during humid summer months, a floor may need to be laid “tight” to avoid unsightly gaps in the winter.  If it is laid in winter, some give may be needed to make room for expansion in the summer.  A capable professional installer will, of course, always take such factors into account.  If you are planning to lay your floors yourself, you may find it helpful to talk with a flooring professional to learn more about moisture and spacing.  Here at Macwoods, our experts are always happy to lend advice when it comes to the details of hardwood.

Acclimation:  For any installation, from floors to doors, it is essential that wood be allowed to acclimate before it is placed in its permanent position.  This will mean letting your new floor “breathe” in the space where it will be installed for a week or so to let it come into balance, both in temperature and moisture content, with the environment where it will live.  For this to be effective, of course, the space in question should be brought to normal conditions for living (air conditioned or heated, depending on the season, for at least a few days) before the wood is introduced.  It is also important that all of the pieces be allowed to acclimate together, either stacked in the box or laid out in a room.  If some pieces are removed and others are not, they will adjust differently, affecting the way they fit together.

After the pre-installation acclimation period, wood will continue to adjust to the environment throughout the year.  For a new floor owner, the changes in the appearance of the floor in this first year may raise some concern, but there is usually no need to be alarmed.  Once your wood has been through a full cycle of seasonal changes, it will settle in to a less drastic cycle and the changes caused by seasonal expansion will be much less noticeable.


Species:  Just like some species of wood are harder than others, some species are also inclined to absorb and release more moisture than others.  For example, a 12” plank of cedar might fluctuate in width about 1/8” from winter to summer while a plank of maple or hickory could fluctuate twice that much.  In a floor, of course, the close set of the planks greatly restricts this movement (you should never have a 1/4” gap in your flooring), but if you are concerned with minimizing seasonal changes in your floors, you will want to choose a species that is more stable.  This is especially true if the temperature and/or relative humidity in your area tend to varies greatly from season to season.

Width:  A piece of wood will expand primarily across the width of the grain as the grains fatten to accommodate more moisture.  The amount of expansion (or shrinkage) you will see is directly proportional to the width of the strip or plank.  So, a 4” strip of any given species will tend to fluctuate about half as much as an 8” plank of the same species.  Again, the installation of the pieces will have an effect on how much each strip or plank actually moves, but in most climates in the U.S., and certainly here in Colorado, you should be prepared to see somewhat more noticeable gapping in plank floors than you would in a floor made up of narrower boards.

Finish:  It has sometimes been suggested that certain types of finish can eliminate flooring movement altogether by stopping the exchange of moisture.  Though there is in reality no finish available at present that can completely stop expansion and shrinkage, the right finish can in some cases help to lessen it.  Moreover, choosing a finish that maintains much of the natural color of a species can make normal movement less noticeable by diminishing the contrast between the finished surface of each board and the wood that may become visible in narrow gaps between boards during drier months.

Cut:  When trees are milled for lumber, there are three primary ways in which a round log may be transformed into a stack of flat boards.  Most often, a log is essentially “sliced” into boards.  This is referred to as plane sawing and results in less waste and the familiar “u” shaped pattern you see in most wood.  In some instances, however, lumber may be “quarter sawn” or “rift sawn”.  These two methods are similar in that boards are cut from the outer edge of a log in towards its heart.  The grain of these boards tends to be more “stripey”, displaying the cross-section of the tree’s growth rings.  Because of the direction of the grain, quarter-sawn wood tends to expand vertically rather than across its width, almost eliminating visible movement.  However, because quarter sawing produces a smaller yield per log, flooring cut in this way tends to be much more costly than plane-sawn.

Egineered vs. solid wood:  One of the primary reasons some people choose engineered flooring over solid hardwood is because of its dimensional stability.  The layers of wood that make up a strip of engineered flooring are intentionally stacked in varying directions so that each layer helps to counteract the expansion and contraction of others.


In truth, there is really just one environmental factor that will seriously affect the movement of your floors—moisture.  This one factor can override all of the factors mentioned above and is so important that we have written an entire post on maintaining healthy levels of relative humidity (RH) in your home.

Just like the air, wood has a moisture content that needs to be maintained at certain levels to avoid excessive expansion and contraction, warping, cracking, and other terrible things.  Fortunately for wood lovers, the moisture content of wood is directly related to the relative humidity of the air around it, and keeping the latter at healthy levels will almost always keep the former stable.

Wood cuts image courtesy of Ron Trout, Portable Sawmill Service