Hygroscopic Properties of Wood
Wood products are derived from living trees, therefore wood products possess the ability to respond to fluctuations in atmospheric humidity. Moisture is the most common cause of damage to wood floors. To keep floors at their optimal strength and appearance, relative humidity of indoor air should always be monitored with a hygrometer, usually attached to a thermometer. Dimensional issues that can arise from moisture and temperature fluctuations from the wood shrinking and swelling are: cupping, checking, splitting, cracking, crowning, and buckling.
Atmospheric humidity determines the moisture content of wood, and moisture content determines the dimension of wood. Outdoor weather conditions affect the humidity in the air. In contrast, humans control the indoor environment through heating and cooling. The major issues that arise do so because of seasonal temperature changes.1 However, different parts of the world will have different moisture conditions, and there are none so vastly different conditions as that in the U.S. Here in the Northeast, where PID Floors showrooms are located, it is recommended to keep indoor relative humidity at a range from 30%-60%. Always consult your wood floor supplier on the proper range for your zone, and the conditions needed for the specific wood you have installed. Different wood species have slightly different requirements.
In the summer, air usually holds an abundance of moisture due to high temperatures. When the warm air is cooled, the capacity of the air to hold moisture is reduced, the relative humidity rises even higher.1 One easy way to combat this problem is to have a dehumidifier turned on in the space with high relative humidity. A dehumidifier will draw the excess moisture out of the air.
In the winter, air has a low absolute humidity. When the cold air seeps indoors, the occupants heat the air up without adding moisture. Therefore, relative humidity drops, and the air is dried.1 In contrast to the easy summer solution to keeping relative humidity constant, is to run a humidifier in the winter months. A humidifier will add moisture to the air.
More complex ways to deal with both summer and winter moisture issues is to find air leaks in the building envelope and seal them to reduce air exchanges between indoor and outdoor environments. Installing high performance insulation can seal the building from outdoor air conditions. Another high-performance building retrofit is to replace all the traditional windows with triple glazed windows. Triple glazed windows can reduce condensation indoors and keep relative humidity constant during winter months.2
Acclimation is quite possibly the most crucial portion of installing new hardwood floors. If this step is not properly done, moisture issues will arise. Yet, keep in mind, that even if all of the wood floor manufacturers’ requirements are followed, acclimation-type issues can occur. A major misconception across all installer professionals is that they let the wood flooring products acclimate for 2 weeks. The proper way to acclimate wood flooring products is to check if the moisture content of the product has equaled the indoor equilibrium moisture content. For example, if a product arrives to a project site with a moisture content of 9%, and the indoor equilibrium moisture content is 7%, then the product needs to acclimate to 7% moisture content.3
Engineered Wood Floor Misconceptions
Even though engineered wood floors are more structurally stable than solid wood floors, a popular misunderstanding is that engineered wood floors do not need to be cared for as solid wood floors do. There are many issues that can occur to engineered wood flooring such as: delamination, face-checking, splitting, and dry-cupping. Although engineered wood floor products will outperform solid wood floors in the case of cupping/gapping, Moisture Content and Relative Humidity of the environment should not be ignored.
Considerations to Keep in Mind
Here are a few tips to keep in mind when installing hardwood floors:
- Identify the expected year-round interior environmental conditions of the project site. Can the manufacturer’s Relative Humidity range be met?
- Identify the expected impact of environmental controls such as: air conditioners, humidifiers/dehumidifiers, seasonal changes in the humidity of the geographic region.
- Installation of floating floors should be left in the factory wrapped packaging until installation [Exposure to the environmental moisture conditions may prevent the tongues from fitting into the grooves.]
- Solid wood floors should be unwrapped from the factory packaging and allowed to acclimate.
- Engineered floors require that the project site meets the conditions outlined in the manufacturer’s recommendations regarding the Relative Humidity.
- Installers should measure and know the moisture of the flooring and of the sub-floor material, the Relative Humidity and the Equivalent Moisture Content of the space.
- Humidity can vary from room-to-room.
- In an engineered product, the wear layer (top layer) and core layer may have different Moisture Content levels, which may cause an imbalance of the product.
- Installing hardwood floors in the middle of winter or summer will cause movement in the floor.
Dew Point / Relative Humidity / Temperature
Dew point is the temperature at which air is cooled to that causes saturation. Dew point and relative humidity are related through temperature. When ambient air temperature and dew point are the same, it causes Relative Humidity to be at 100% which creates liquid dew. Relative humidity rises as the temperature falls then more water vapor condenses as the temperature decreases. When moisture content remains constant, temperature increases, relative humidity will decrease. If temperature and pressure rises, the dew point rises and relative humidity decreases.
For a dew point calculator please refer to: http://www.dpcalc.org
Dew point is an important factor to consider in your indoor environment because it will cause condensation and ruin building materials. Dew point has an affect on the comfort level of occupants. Please refer to the table below.
Suggestions to Prevent Common Water Damage to Wood Floors
- Place barrier floor mats at all building entrances to reduce the amount of soil, pollutants and moisture that gets tracked into your home, office, or retail store.
https://www.epa.gov/iaq-schools/controlling-pollutants-and-sources-indoor-air-quality-design-tools-schools?utm_content=&utm_medium=email&utm_name=&utm_source=govdelivery&utm_term=#Entry Mat Barriers
- Installing low flow sink faucet fixtures can reduce the amount of water that splashes out onto the floors in front of the kitchen and bathroom sinks. These areas tend to have moisture damage.
- Using a hygrometer to keep indoor relative humidity in check. When people can see the actual status of indoor conditions, they are better equipped to remediate issues as issues occur.
- Humidifier / Dehumidifier – Use a humidifier in the winter to return moisture to the air as indoor environments are heated. Use a dehumidifier to combat extra moisture in the air in the summer season.
1Hoadley, R. Bruce. (2000). Understanding Wood: A Craftsman’s Guide to Wood Technology. Newtown, CT: Taunton Press.
2Alter, Lloyd. (2017). Does Embodied Energy Really Matter in Green Building? [accessed 2017 Feb 10]. http://www.treehugger.com/slideshows/green-architecture/does-embodied-energy-really-matter-green-building/page/11/#slide-top
3DeWitt, Craig. (2010). Acclimation is NOT a Time Thing. [access 2017 Mar 8]. https://www.woodfloorbusiness.com//inspector-blog/acclimation-is-not-a-time-thing.html