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Moisture Control & Acclimation

Understanding Humidity Levels

Hardwood flooring is a natural product that will respond to different humidity variations. This means that even though the wood has been dried, cut, and processed into flooring material, the hardwood may expand or contract because of moisture. A change in seasons is when these changes become especially noticeable. During warm and humid summers, hardwood flooring expands. During dry winter weather, hardwood flooring contracts. Because this seasonal movement is normal for hardwood products, the best way to reduce such movement is by installing humidity controls and making sure that they function before flooring is installed.

In order to prevent your floor from expanding or contracting, it’s important to keep up with hardwood flooring maintenance. With this in mind, you have to understand how these changes are caused based on the specific climate you live in as well as the climate of your home. But don’t worry, preventing movement of your hardwood flooring isn’t solely based on maintenance. There are also preventative measures that can be taken when your hardwood flooring is installed.

Wood is a hygroscopic material. When wood is exposed to air, it will either dry or pick up moisture until its reactions occur at equal rates with the humidity and temperature of the air. When the moisture is absorbed, the wood will swell. Wood will begin swelling as the moisture levels increase anywhere from 0-30%. When the moisture is lost, the wood will shrink. Shrinkage of wood begins at 25-30% of moisture content. Anything above 25%-30% means that your hardwood flooring is dimensionally stable.

Hardwood does not shrink or swell equally in all directions. A change in moisture content of a piece of hardwood flooring from 0% to 28% will increase the size of the piece approximately 0.1% along the LENGTH of the board, and 5% to 15% change in size in WIDTH of the strip with plain sawn flooring.

Acclimating Before Installation

Acclimation describes the process of conditioning hardwood floor so its moisture content is at the optimal level for the environment it is to be installed. For most wood flooring, the wood floor must be within 4% of the moisture content of your subfloor. For solid wood flooring with planks wider than 3 inches, the flooring should be within 2% of the subfloor. If the wood has a lower content than the acceptable range, it will absorb moisture and swell up. Too high a content causes it to lose moisture, resulting in shrinkage. What you should strive for is referred to as equilibrium moisture content, or the point where the wood will not gain or lose moisture.

Wood flooring typically comes from a region with a different climate than where you live. Furthermore, it’s frequently stored and shipped in environments that are far more extreme than those within the comfort of your climate controlled home. When it arrives for installation, it naturally has a different moisture content and requires time to adjust to its new environment. While most manufacturers recommend around one 7-10 days for acclimation, the actual duration depends on factors such as moisture content at the time of delivery, the type of wood, its dimensions and its finishing method. It’s important to note that not all wood needs to acclimate to its environment — for instance, it could arrive at equilibrium moisture content. Engineered and solid factory-finished flooring often doesn’t require as much acclimation time, provided the environment is within what’s considered average humidity and temperature levels.

If you’re not sure whether your hardwood flooring needs to go through the acclimation process, contact us to speak with one of our experienced representatives that can help you make an assessment.

Winter Time

Because your home is normally heated during cooler months, your hardwood flooring gives up some of its moisture and contracts. Naturally, when this happens, thin gaps can appear between planks. As a homeowner, you should be prepared for this to occur. However, in order to try to prevent these separations, you can install a humidifier in the furnace or bring a movable humidifier into the room. As long as your humidity doesn’t fall lower than 40%, no gaps should appear between your hardwood flooring planks. Generally, once the weather starts to warm up for springtime, heating is turned down and humidity levels will naturally rise. In turn, most of the gaps in your hardwood flooring material will close up on their own.

Summer Time

When spring shifts to summer, your indoor humidity can rise up to 90%, causing your hardwood flooring product to expand. Even just a few days of humidity can cause wood flooring to cup, which means that the edges on the wooden board are higher than its center. Cupping can also happen when spilled water gets absorbed by your hardwood floors. To avoid cupping, keep your indoor humidity levels between 40-60%. High levels of humidity can cause hardwood flooring to expand significantly, sometimes causing the affected boards to lose their structural integrity and crack. That’s why it’s very important to never allow indoor humidity to rise over 65%. Your hardwood flooring maintenance can be made easy by keeping air conditioners or dehumidifiers running during the humid summer weather.

Planning Ahead

When leaving your home for a long duration, it is important to plan ahead for home conditions while you are gone. Keeping your A/C running while you are out can help prevent excessive change in the atmosphere. Humidifiers & Dehumidifiers are also something to think about to help avoid possible movement in your hardwood floor.

Wood Flooring Expansion and Contraction

Unlike many floor coverings, hardwood flooring material can last the lifetime of the building in which it is installed. As a homeowner, you should note that the number one enemy of your hardwood floor is moisture. Hardwood flooring naturally expands when moisture is present and shrinks when moisture is absent. Although not every reaction is a problem, stated below are some of the common results when water and hardwood flooring combine.

CRACKS BETWEEN BOARDS: When homes are heated, humidity levels plummet. In dry months, cracks can easily develop to the thickness of a dime on a typical solid 2¼ inch hardwood oak floor. These spaces in your hardwood flooring are to be expected and will usually close up as the seasons’ change and moisture returns to the air. If you want to try to combat these cracks between boards, try installing a humidifier in the furnace.

CUPPING: As with cracks between your hardwood flooring material, both cupping and crowning are also natural reactions to moisture. Cupping happens when the edges of a hardwood flooring board are higher than its center. Humidity is usually the culprit, although cupping can also happen if water is spilled onto the floor and absorbed into the hardwood flooring material. This moisture causes the wood to swell, crushing the boards together and deforming them at the edges. In order to repair your damaged hardwood flooring product, the cause of the moisture needs to be controlled. To speed up the drying process, use a fan and recoat your hardwood flooring with a flooring dealer approved finish once completely dry. This will leave your hardwood flooring material looking as good as new!

CROWNING: This is the opposite of cupping. Instead of the middle of the board being the highest point, the edges now surpass the center. This occurs when the surface of your hardwood flooring material encounters moisture and can also occur when flooring has been sanded too soon after it has cupped.

BUCKLING: Buckling is one of the most extreme reactions that can occur with your hardwood flooring. Buckling happens when the floor pulls away from the subfloor, up to heights as high as several inches. In such cases it is still possible for hardwood flooring to be repaired rather than replaced, depending on the severity.

Preventing Moisture Problems

Controlling humidity is the most important factor in preventing problems with moisture and your hardwood flooring material. Proper hardwood flooring maintenance will also go a long way. To prevent moisture issues, it is best to:

  • Buy a “floor care kit” recommended by your hardwood flooring professional and clean your wood flooring with a cloth lightly dampened by the recommended cleaning product. Your flooring manufacturer will provide directions for use.
  • Clean your hardwood flooring material only when necessary. Do not clean your wood floors with water or water-based products on a regular schedule.
  • Never damp mop on a wood floor! The water deteriorates the wood and finish.
  • Never let a water spill dry on the floor.

Radiant/Hydraunic Heating

Radiant heating for floors is a system designed underneath your floor to assist in warming the house. This process is done in many different designs in todays world, but each one can be potentially harmful to your hardwood floor. Because of this, Radiant/Hydraunic Heating is NOT covered by warranties offered on products sold by Nature Wood Floors. This does not mean a hardwood floor cannot work over these heating systems, but it is important to understand completely the product you are buying before making a purchase.

Radiant heat is not recommended for application with most solid woods since being a natural material, exposure to high levels of moisture and extensive fluctuations in temperature result in contractions and expansions. The presence of dry heat directly under solid wood floorings can, therefore, lead to quick drying out and contraction of the wood, which might result in cupping issues or the development of large gaps between floorboards. This is why most warranties by manufacturers rarely cover installations over radiant heat. If a solid wood is required over radiant, it is best to stick with narrow planks sizes and Rift & Quartered Sawn lumber.

Engineered wood flooring is, in general, more dimensionally stable than solid wood flooring. However, not all engineered wood flooring is recommended or appropriate for use over radiant heating systems. Engineered flooring with a less-stable wear layer species such as hickory, maple, and most exotic species are not normally best suited over radiant heat unless otherwise suggested by the flooring manufacturer. The cut and thickness of the wear layer may also affect how the floor performs over radiant heat. Follow the flooring manufacturer recommendations for maintenance, environmental (T and RH) requirements, surface temperature requirements, and whether or not each specific product is intended to be used over radiant heat.

Successful wood floor installations occur when the radiant heat system design engineer, the radiant heating system installer, the wood flooring installer, and the end-user all communicate and fully understand what is required for the entire flooring system being installed. This communication should include which type of wood flooring to use, what installation method to use, understanding how this heat source may impact the wood flooring, what precautions to take before, during and after installation, and consistent communication among all parties when any changes take place to any part of the system. Before the final purchase is made, it is up to the purchaser and end-user to have a clear understanding of the flooring product use and maintenance requirements, as well as the radiant heating system features, limitations, and capabilities, and how all of these work together within the system, to stay within the necessary parameters.