Moisture Under Hardwood Floors: Warning Signs and Prevention Tips

Moisture Under Hardwood Floors: Warning Signs and Prevention Tips

When it comes to hardwood flooring, moisture is your biggest enemy. As a natural product, wood reacts to environmental factors like moisture or temperature, and both hardwood and engineered wood are at risk of moisture damage. The bad news is that moisture damage is often irreparable, and the hardwood planks can have permanent damage that requires them to be replaced. That’s definitely not what your clients want to hear, especially since some hardwood species can be quite expensive. 

Hardwood flooring is incredibly sturdy and durable, and very aesthetically pleasing at the same time. It can stay in top shape for decades, if properly cared for, with regular cleaning and upkeep. However, moisture damage can be hard to spot, especially if the damage is happening beneath the hardwood floors, and by the time the first signs of damage start to show, it can be too late. So, how can you ensure that hardwood floors are protected from moisture and water damage, and how can you recognize the warning signs?

Water damage warning signs 

If water or moisture damage is minimal, say someone spills a glass of water or some kind of liquid onto the hardwood floor, it can be fixed without any long-term damage to the integrity of the wood. As long as any spills are cleaned immediately, and the floor is allowed to properly dry and air out, and the damage is surface-level only, there won’t be any significant impact to the hardwood. The area can be cleaned, dried, and recoated, if needed, to protect the floor from any future damage. 

However, if spills or other accidents are not resolved, and water starts to infiltrate the hardwood planks, it can cause damage that is hard to see with the naked eye, and thus hard to repair before it gets worse. But there are often recognizable signs of water damage to a hardwood floor, signs that an industry professional might notice before the homeowner or business owner. The trained eye will be able to spot these warning signs and pinpoint the cause behind the damage, and find a solution. 


When the edges of a hardwood board rise higher than its center due to moisture damage causing the wood to warp, this is called cupping. This often occurs after water is spilled onto the floor and is absorbed into the wood, causing the planks to expand and pace pressure against each other. As a result, the edges of the planks rise up and become deformed. This happens because the surface of the wood boards dry faster, while the bottom and the edges take a lot longer to dry and hold more moisture. Cupping can also occur when relative humidity levels are high for a prolonged time.


Crowning is the opposite of cupping, and it results in the center of a hardwood plank rising higher compared to its edges. Crowning can almost look like the wood is swelling or bulging, and it’s often caused by moisture exposure or an imbalance in moisture levels throughout the wood planks. If the hardwood floor is exposed to water or high humidity levels for a prolonged period of time, moisture can start to saturate the wood and cause crowning, which sadly can’t be reversed. 


Buckling is the most extreme warning sign that shows you water has caused significant, irreparable damage to hardwood flooring. It doesn’t happen as often as cupping or crowning, but it’s more severe, and it occurs when the hardwood floor has been flooded or submerged for an extended period of time. The prolonged exposure to water can cause the hardwood floors to pull up and separate from the subfloor, causing visible bulging and warping across the floor surface. 

There is still hope for the hardwood floor, even in this extreme scenario. Once the standing water is removed, parts of the floor or the entire floor can be removed to allow air to circulate and the wood to dry. Although it might take a long time, once the wood has dried to an acceptable level, the floor can be repaired, unless there already is extensive damage. In many cases, the entire floor (and the subfloor, as well) will have to be replaced. 

Preventing water and moisture damage to hardwood floors

While moisture can be considered ‘enemy number one’ when it comes to hardwood flooring, damage can be prevented and mitigated if proper action is taken at the right time. 

The first step to preventing water damage to hardwood flooring is to properly install and thoroughly check the subfloor prior to installing the hardwood planks. Whether it’s concrete or wood, the subfloor plays an important part in protecting the hardwood from damage and extending its lifespan. 

The subfloor should be completely dry before installing the hardwood on top of it; sometimes the subfloor looks dry, but there can still be moisture present, so it’s important to thoroughly check it and give it time to fully dry. 

The best way to test if the subfloor is really dry is to use a wooden floor moisture meter to measure the moisture content. If you’re working with a concrete subfloor, the moisture content, or MC, should not exceed 6%. If the subfloor is made of wood, plywood, or joists, the MC should be under 16%. Keep retesting regularly until the moisture content levels are within these limits; then it’s safe to install the hardwood floor over the subfloor. 

Besides making sure that the subfloor is completely dry before installing the main floor, it’s important to also ensure that it is flat, level, and clean. A level subfloor is crucial to ensuring that the hardwood floor above will also be level and flat, thus avoiding future issues. There also needs to be an expansion gap around the edges of the room where the wood subfloor and floor is installed, because wood will expand or contract depending on changes in temperature or humidity. 

The hardwood planks need to be acclimated to the humidity and temperature in the room they’re being installed in, to avoid any issues with warping or cupping down the line. The planks need to be stored in the room, stacked on top of each other with space in between, to allow them to acclimate to the humidity level in the air.