Cleaning & Care

Why is My Floor Gapping?

Seeing gaps in your wood floor?

Frequently with wood flooring, gaps can signify a problem. The issue isn’t necessarily with the gap itself, but in understanding the underlying cause.

Here’s a quick run-down of what makes a normal gap.

Environmental / Seasonal Gapping

The Cause:

Gaps typically show up during winter when the air is dry but returns to normal in the spring. This happens due to seasonal changes and is normal for most wood floors.

Low relative humidity brought on by naturally dry winter weather combined with firing up the heater causes indoor air to become dry. The result is the drier air draws moisture from its surroundings including the wood flooring. For solid wood floors gaps tend to vary in size relative to the width of the boards.

Gap in a hardwood floor
One of the leading causes of flooring gaps in the winter is the lack of moisture in the air.

Wider plank floors will show gaps much more than their narrower counterpart. Light-colored and square-edge flooring will show gaps more than dark or beveled floors. With engineered products, you may notice the sides curling or the ply backing separating.

Homeowners that keep their house within the 35-55% relative humidity range with an in-home humidifier will help reduce the occurrence of winter-time gaps.

How Gaps Affect a Wood Floor:

A homeowner may worry because of gaps in their flooring. Most of the time during the dry season, flooring gaps are due to low moisture content in the wood – caused by low relative humidity inside the home.

By understanding this, it becomes easier to explain to a homeowner the importance of having a hygrometer and humidifier to help keep their home and floors stable during the dry winter months. When spring rolls around, gaps will generally begin to close as the floors regain moisture from the higher RH in the air. See why you should buy a humidifier and pass it along to your customers.

Infield Expansion Gaps

The Cause:

Some gaps are intentionally included during installation by the flooring installer. Wood flooring is an organic material that expands and contracts, just like trees do. Under certain conditions in the installation process, intentional gaps running the length of a row of boards are left to allow the flooring to expand during the more humid part of the year. Major problems could result if expansion rows are not left during winter installations.

Man installing hardwood flooring
Depending on the time of installation, gaps may be purposely created to avoid future problems with the floor.

One of these instances is winter time installation when the wood’s moisture content is at its lowest. By installing with some intentional gaps, this allows for the natural expansion and contraction of boards from summer to winter. The wider the plank, the more critical this infield expansion gap becomes. If this allowance is not made, the boards may cup and cause damage during the summer.

How It Affects a Wood Floor:

Imagine you are planning to install a floor during winter. The moisture level of the wood is at its lowest and the air is dry. No amount of acclimation would make much difference since the environment and flooring is all dry.

You have two options at this point:

First, install the floor with no infield expansion gaps. In the spring as humidity increases, it starts to expand and the floor boards take on moisture. By summer, you can see that the floor is cupping and nearly buckling due to expansion.

The second option is to install with expansion gaps. This is usually done by installing with a dime, washer, or thin weed-eater line placed between the flooring boards leaving the necessary gap. When summer comes around, the floor expands without damage.

Jobsite Problems

Jobsite conditions, and decisions made before the floor is installed can also cause problems.

Let’s start off with acclimation. All wood products need a chance to adjust to their new home with the climate control system up and running. This is not a time for shortcuts. Acclimation takes time, but it is the the responsibility of the install contractor to properly follow manufacturer guidelines to ensure success.

Flooring tools being used for hardwood installation
Sometimes the conditions of the jobsite, such as climate issues or subfloor problems, can lead to gapping down the road.

Acclimation is not limited only to the flooring product. Subfloors also need to be checked for proper moisture content and acclimated if necessary. The gold standard for prepping the subfloor is that they must be clean, dry, sound and flat (level). Give ample time and attention to these steps before you lay the first board.

Proper job site preparation and following manufacturer and industry recommended installation instructions are the best kind of insurance against problems down the road. See our installation guide that links to all of the recommended instructions for our prefinished flooring lines.

It is important to pay attention to details during installation. Here are three areas to watch closely:

  1. Start installing the flooring straight and you’ll be good to go. Improper alignment of the wood floor will create gaps at the ends and sides of the flooring.
  2. If you are gluing down the floor, pay attention to the trowel you are using. Too much or too little adhesive can have adverse effects. Check with your flooring adhesive manufacturer for the trowel that achieves the right spread rate and avoids potential for gapping. Remember to change your trowel regularly – they will wear down quickly which will cause a change in your spread rate.
  3. If you are nailing or stapling down the floor, be sure to use the correct air pressure for the fastener you are nailing. Too low of pressure could leave the fasteners seated too high, while too high of pressure could split the tongues. Both of these issues cause boards to not sit flush.

Did you know that using the wrong fastener or air pressure can also cause squeaks? Find out more about how to stop squeaky floors by using the right fastener here.

Manufacturer’s Issues

The Cause:

The last culprit for gaps comes from the flooring manufacturer and generally with solid flooring material.

The most common issue is mis-milling. This occurs when lumber is milled into specific widths but for various reasons a machine molder or saw could be malfunctioning causing taper from one end of a board to the other.

Insufficient kiln drying before flooring is milled to the correct range of 6-9% moisture content will result in delayed shrinkage as the material completes drying whether its been installed or stored in a warehouse. If this improperly milled flooring is installed without the installer checking the MC of the flooring, he would along with the manufacturer be responsible for the gaps. In this case the gaps will never close up and the flooring will need to be replaced.

Flooring mills that process lower grade lumber into flooring are allowed a % milling defect. As a result any flooring contractor who does not inspect each board and cull out problem boards during install can actually install problems into a floor. Gaps and other character defects like splits, large knots, could result in homeowner complaints at the completion of the job. Lower grades of flooring where tolerances are less and more defects are allowed could result in gaps during or after install. In most cases, installers should communicate with the homeowner and set their expectations for what is and isn’t acceptable.

Determining the real cause for gaps can take some detective work. In many cases, when gaps are normal, wood filler can be used to fill in the gaps prior to staining and finishing the floor.

Wood drying outside at a lumber mill
With lower grades of flooring you are more likely to experience gaps in the long term.

How It Affects a Wood Floor:

Years after an installation a homeowner may call saying gaps have recently shown up in their flooring. Remember the filler? As the floor goes through seasonal expansion and contraction cycles, some of the wood filler may have been pressed out revealing a gap. A quick remedy is wood putty that can be used to replace the filler and get the floor looking like it originally did.

How to Fix Wood Floor Gaps

When it comes to gaps before the installation, the installer needs to make sure that the flooring is milled correctly and that it is installed in accordance with the manufacturer’s guidelines. Measure the width of a random sample of the flooring material at each end and the center of the boards. Check the moisture content in a random sample of boards ensuring the flooring is within normal range for the species being installed. Remember – installation is acceptance.

It’s also important to properly acclimate the floor with the humidifier on and thermostat set to living conditions (typically 35-55% relative humidity and 60-80 degrees F).

For gaps that occur post-installation, the best remedy is to install a whole home humidifier. Keeping the home between 35-55% RH, will keep the floors from contracting during dry seasons. You can track how well the humidifier is working by purchasing a hygrometer that will measure the RH.

If you see gaps in your flooring, consider whether they are intentional (infield expansion), humidity-related (seasonal) or an installation error.