What happens if wood flooring absorbs moisture from the subfloor?

Author: Isabel Sporer  |  Last update: Sunday, June 8, 2025

Crowning Hardwood Floors Crowning is the inverse of cupping. When excess moisture is absorbed into the floorboard, the center of a floorboard can rise or swell above the edges. This also results in an uneven floor and, if left untreated, can cause long-term damage to the integrity of your hardwood floors.

Is the subfloor ruined if it gets wet?

A wet subfloor doesn't always need to be replaced, but it must be thoroughly dried and assessed for damage. Use fans and dehumidifiers to dry it out. If the subfloor is swollen, warped, or has mold growth, replacement is necessary.

What happens if water gets under a wood floor?

Water damage can lead to a condition commonly known as “cupping” in hardwood floors. This occurs when excess moisture permeates the hardwood, primarily affecting the unfinished underside of the boards.

How to tell if there is mold under a wood floor?

Signs of Mold Under Floors
  1. Discoloration: Patches of yellow, green, or black can signal mold growth.
  2. Warping: Uneven or bulging floorboards suggest moisture buildup, a breeding ground for mold.
  3. Peeling: If you notice your floor's finish peeling or bubbling, it could be due to mold underneath.

How to fix moisture under a hardwood floor?

Drying water under a wood floor requires proper ventilation and dehumidification. Use fans and dehumidifiers to circulate air and remove moisture from the affected area. Additionally, you may need to lift and aerate the floorboards to facilitate drying thoroughly.

What Causes Wood Floor Cupping & What To Do

What pulls moisture out of wood floors?

Use a dehumidifier placed at the highest setting possible to dry the floors. Place it in the center of the room and leave it on for at least 24 hours. Next, place fans around the room so the entire surface receives the blowing air. Place the fans at the highest settings possible.

How to fix a damp subfloor?

Sub floor ventilation systems are very effective in homes that experience a continuing musty odour or where there is mould on shoes and clothes in wardrobes or on furniture in living spaces. Subfloor ventilation can remove ground moisture from underneath raised floors, creating a drier and warmer sub floor area.

What does mold on subflooring look like?

Subfloor mold can appear as dark spots or patches beneath flooring materials like carpets, vinyl, or laminate. It often grows on plywood or OSB substrates, common since the 1950s. The presence of subfloor mold can be hinted at by a musty odor.

How long does it take for mold to grow under wood floors?

Particularly vulnerable to water damage is wood. It is a natural material susceptible to decay and mold when exposed to moisture or water. The wood is prone to develop mildew and mold during the first two hours to seven days of being exposed to moisture and water.

What kills mold under flooring?

Borax is highly recommended as a mold remediation product.

What draws moisture out of wood?

After thoroughly towel drying the floor, add absorbent material like sawdust, baking soda, or kitty litter. Spread a generous amount of the material over the affected area and let it sit overnight. The absorbent material helps to draw out any remaining moisture from the wood and makes it easier to dry.

Will insurance pay for water damage to wood floor?

Homeowners insurance generally covers water damage that's sudden and accidental. For example, if a pipe bursts or a washing machine overflows and damages your floor, you may be covered. But if the water comes from flooding, standard homeowners insurance typically won't cover it.

How long does it take to dry out a subfloor?

Most wood floors flooded with water will take weeks or more to fully dry out. In some circumstances, especially with a wooden subfloor, removing the wood flooring is necessary to fully dry out the subfloor.

How do I know if my subfloor is ruined?

When Should You Replace Subfloors? There are many signs that your damaged subfloor should be replaced with a new subfloor. These include squeaks and other noises, cupping or warping, cracked or popped tiles, sagging or unevenness, the smell of mold or mildew, or bubbling tile.

How long does it take for water to damage wood floors?

As time passes, the moisture trapped within the wood creates an ideal environment for mold and mildew growth. Within 24 to 48 hours, mold spores can begin to colonize, posing health risks to residents and further compromising the structural integrity of the flooring.

How can you tell if mold is under hardwood floors?

Signs Of Mold On Hardwood Floors
  1. Musty Odor – A tell-tale sign of mold growing beneath your hardwood flooring is a musty scent. ...
  2. Discoloration – If you start to notice discoloration or staining on the surface of your hardwood flooring, it could be a telltale sign that mold is growing beneath it.

What are the 10 warning signs of mold toxicity?

Although symptoms can vary, the most common symptoms seen in people exposed to mold indoors include:
  • Nasal and sinus congestion.
  • Eye irritation, such as itchy, red, watery eyes.
  • Wheezing and difficulty breathing.
  • Cough.
  • Throat irritation.
  • Skin irritation, such as a rash.
  • Headache.

How long can wood be wet before mold?

mildew and mold will develop within 24-48 hours of water exposure. Even worse, it will continue to grow until steps are taken to eliminate the source of moisture, and effectively deal with the mold problem.

How much does it cost to replace mold on subfloor?

Subfloor Cost per Square Foot

Subfloor replacement typically costs about $3 to $10 per square foot. This range can vary based on labor costs, which will add $25 to $30 per hour, and the type of subflooring you choose.

Does homeowners insurance cover mold?

Homeowners insurance doesn't usually cover mold damage or removal unless it's the result of a covered peril. If the mold in your residence was caused by something sudden or accidental, such as a bursting pipe or some other covered incident on your policy, you may be protected.

What is the best mold remover for subfloor?

Treat exposed molded subflooring with a mixture of 1 cup of borax and 1 gallon of water or an EPA-registered mold removal product. Spray the solution on the moldy subfloor. You can also soak affected subflooring with a brush broom. Wait 10 minutes, scrub the area, and repeat the process two more times.

Is subfloor ruined if it gets wet?

In most cases, damaged subflooring doesn't need to be replaced. However, in the event of extensive water damage from flooding or extended periods of exposure to moisture, damaged sections may need to be removed to avoid mold and ensure structural integrity.

What is the best way to ventilate a subfloor?

Simple air vents (commonly brick type vents with small holes in them) strategically positioned around the sub floor perimeter is the most common measure to ensure sub floor ventilation. This uses natural (or passive) cross flow of air, as shown in the below image.

How do you remove moisture from subfloor?

The first way that you can fix a subfloor moisture problem is by removing the finished floor and exposing the subfloor. Make sure that an HVAC system is installed or use a dehumidifier, and then, let the subfloor dry until the moisture levels have gone down.

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