Measuring twice and cutting once sometimes isn’t enough when installing millwork. Wood is hygroscopic, expanding as relative humidity levels increase and contracting when it loses moisture. Professionals refer to the relationship between wood and humidity as equilibrium moisture content (EMC). Construction drying solutions prevent EMC changes, allowing you install millwork without the risk of bowing, splitting or gap formations.
Relationship Between Moisture Content and Relative Humidity
As the relative humidity in the environment increases, so does the moisture content in wood and the EMC. There are some basic rules that experienced woodworkers remember during a project regarding EMC, such as:
- Wider boards expand more than thinner ones.
- Quarter sawn lumber expands and shrinks half as much as flat sawn lumber because of the orientation of the annular rings.
- Always use a moisture meter to determine if the moisture content of lumber is within the acceptable range of 9 to 10 percent. The ideals levels are 6 to 8 percent.
- The temperatures and humidity levels outside a building affect wood as much as the conditions inside.
- Different species of wood expand and contract differently.
- The application of finishes does not prevent expansions and contractions in millwork.
- The ideal relative humidity for construction projects to protect lumber is between 30 and 60 percent.
Just as high humidity levels and lumber with high moisture contents are not good for construction projects, the same is true of dry ambient conditions and wood that’s too dry. While dry wood isn’t always a problem for inside trim, it can create significant issue when you install it on the outside of a building and warps as it acclimates to seasonal conditions. When relative humidity levels are too high or low, responsible contractors use humidity control for construction sites to prevent adverse changes in millwork.
Construction Drying and Wood Storage
The environment in which you regularly store millwork is just as important as its environment at a construction site. Stored lumber requires proper ventilation. During times when the surrounding environment is cold, dry or humid, you may need temporary climate control to maintain the lumber’s EMC level. Some professionals regularly monitor the relative humidity in a storage area and the moisture content of the lumber inside to ensure environmental controls are at the correct settings.
When storing millwork on a construction site, there are factors unrelated to the weather that could increase the environment’s relative humidity and the lumber’s moisture content, such as wet concrete, plaster or drywall. Humidity control for construction sites creates conditions that regulate temperatures and humidity levels, promote the drying of construction materials and prevent changes in millwork.
Construction drying makes millwork more reliable and predictable when ambient conditions are not ideal. The temporary climate control solutions that Polygon offers prevent wood movement problems, costly repairs and unhappy clients. Its custom dehumidification and heating systems, along with moisture mapping, ensure that the moisture content in your lumber is at an optimal level and maintained at its Standard Service Life Condition (SSLC). Contact Polygon to learn more about its construction drying solutions and to schedule a consultation.
[Photo from JDH Rosewater via CC License 2.0]