In recent years, the focus of moisture-related issues in the flooring industry has largely revolved around concrete subfloors, but an often overlooked culprit is moisture in wood subfloors. This problem is growing in importance, particularly with the increasing use of wood in residential flooring systems and the effects high humidity can have on these materials. In this article, we will explore the causes and consequences of wood subfloor moisture, as well as how to effectively manage this issue to ensure the longevity of your flooring installations.
The Growing Issue of Wood Subfloor Moisture
We are currently experiencing a period of high humidity, especially during the warmer months. Homes, both newly constructed and older ones, without proper climate control are particularly susceptible to moisture problems. This moisture can significantly affect wood subfloors, potentially causing issues with newly installed flooring, including expansion, buckling, or joint show-through. As the moisture content in the wood increases, so does the risk for floor-related failures. This makes understanding and managing wood subfloor moisture more critical than ever before.
It is essential for every installer to have a moisture meter for checking wood subfloors. These tools have become the most important instruments for flooring installers but are often neglected in the field. Moisture meters are vital not only for hardwood installers but for all flooring trades. These meters can help detect moisture damage in subfloors, measure the moisture content of wood subfloors prior to installing any flooring, and ensure that the hardwood is at the correct moisture level in relation to the subfloor.
Types of Moisture Meters
There are two main types of moisture meters used for checking wood subfloors: Pin (Invasive) and Pinless (Non-Invasive).
- Pin or Invasive Moisture Meter: The traditional and older of the two, this meter uses pins that measure electrical resistance across opposite sides of the pins inserted into the wood. Pin meters generally measure moisture levels ranging from 6% to 30%. These meters are ideal for precise moisture readings at specific points in the wood but can leave visible holes in the material.
- Pinless or Non-Invasive Moisture Meter: This newer style of moisture meter uses electromagnetic signals to detect moisture without physically penetrating the wood. Non-invasive meters can be moved across large areas of the floor to locate wet spots or detect overall moisture levels. They are less intrusive than pin meters and can be used on rough surfaces without causing damage. These meters are especially useful for large areas where visible pinholes would be a concern.
It is important to ensure that the moisture meter you are using can accurately read OSB (Oriented Strand Board) subfloors, as this material has different moisture absorption characteristics compared to solid wood.
Why Should You Test Wood Subfloors?
Wood subfloors are naturally porous materials, and when they absorb moisture, they tend to expand. This expansion can cause serious issues for flooring systems. For example, flooring can begin to move, buckle, or show gaps between joints, which compromises both the appearance and functionality of the floor.
One common scenario occurs in homes with new construction during the hot, humid summer months. If flooring is installed on a subfloor that has absorbed excess moisture, the floor may appear fine initially. However, once the heating system is turned on in the fall, the moisture in the subfloor starts to dry out. As the subfloor contracts, the previously installed flooring may buckle because there is no longer sufficient expansion space to accommodate the shrinking subfloor. This can lead to significant damage to the flooring.
Another situation that exacerbates the problem is flooring installed over crawl spaces. These areas are particularly prone to moisture accumulation, especially if the crawl space is not properly ventilated or sealed. A lack of ventilation traps moisture, which can seep into the wooden subfloor and cause it to swell, leading to flooring failure.
How Many Readings Should You Take?
To ensure accurate moisture readings, it’s essential to follow industry guidelines. Hardwood flooring suppliers recommend taking a minimum of 20 readings per 1,000 square feet of subfloor area and averaging the results. This practice is valuable not only for hardwood installations but for all types of flooring, including laminate, vinyl, and tile. Taking multiple readings across the subfloor ensures that no localized moisture issues are overlooked and provides a more accurate assessment of the overall moisture content.
How Does Wet Subfloor Affect Flooring?
The effects of a wet subfloor on flooring materials can be likened to the way a paper towel absorbs moisture from a damp sponge. When moisture-sensitive materials such as hardwood or plywood underlayment are installed over a wet subfloor, they will absorb the moisture and expand. This can lead to a variety of flooring problems, including:
- Plywood Underlayment Joint Show-through: When a dry underlayment is installed over a wet subfloor, the moisture in the subfloor is absorbed by the underlayment, causing it to swell. As the underlayment expands, the seams can push up, creating visible joint show-through. This is particularly noticeable in vinyl flooring installations, where the seams can be seen through the surface.
- Cupped Hardwood: Hardwood flooring, when installed over a wet subfloor, can experience cupping. This occurs when the bottom of the hardwood absorbs more moisture than the top surface, causing the edges to rise. Over time, this can lead to the hardwood buckling or even lifting off the subfloor entirely.
These types of issues can be prevented by ensuring that the moisture content in the subfloor is properly managed before installation begins.
What Are Your Subfloor Moisture Limits?
Each type of flooring product has specific moisture content limits for the subfloor, and these limits vary depending on the manufacturer. For instance:
- Hardwood Floors: Most manufacturers recommend that the moisture level of the subfloor should be no higher than 12% or 13%. Additionally, the moisture content of the hardwood should be within 2-4% of the subfloor moisture level. For plank hardwood (3¼” wide or more), the difference should be no more than 2%, while for strip hardwood (2¼” wide), the difference should be no more than 4%.
- Floating Floors (LVT, Cork, Laminate, Hardwood, Ceramic, Vinyl): Subfloors with a moisture content over 13% will likely cause too much movement for floating floors to accommodate. As the subfloor shrinks, the flooring’s expansion zone may be compromised, leading to buckling and other problems.
- Glue-Down Floors: Similar to floating floors, subfloors with moisture content above 13% can cause issues for glue-down floors. Excess moisture may lead to adhesive failure or cause the subfloor to shrink, resulting in show-through.
How Do You Address Subfloor Moisture Issues?
Dealing with subfloor moisture requires a two-pronged approach:
- Acclimation of Flooring Products: Acclimating flooring materials to the environment where they will be installed is crucial. This allows the materials to adjust to the ambient humidity and temperature, ensuring they do not absorb excessive moisture from the subfloor after installation.
- Proper HVAC System Functionality: Getting the HVAC system up and running before installation helps initiate the drying process in the subfloor, reducing excess moisture in the environment.
Documentation and Monitoring
Once moisture readings have been taken, it is essential to document the results for future reference. This documentation can serve as a useful record in case problems arise later on. For example, if the subfloor moisture content was measured at 10% during installation and the flooring begins to fail months later, checking the moisture content at that time can help identify the source of the problem (e.g., leaks, flooding, etc.).
When documenting moisture readings, it is important to record the following details:
- Customer information
- Installation address
- Date and time of readings
- Specific moisture readings
- Locations of readings
- Photos of the readings and any visible issues
Conclusion
Wood subfloor moisture is a critical factor in ensuring the long-term success of flooring installations. By using moisture meters, testing subfloor moisture content, and following industry guidelines, installers can avoid costly failures and provide their customers with high-quality, durable flooring. Additionally, proper documentation and ongoing monitoring can help prevent future issues and support claims should problems arise. Taking the time to properly manage moisture in wood subfloors is an investment in the overall integrity and longevity of the flooring system.