Humidity & Moisture
Everyone knows wood comes from trees and that it can behave differently than we wish. In a tree, wood serves many functions; it provides a strong,durable, and resilient structure to support the tree’s growth, thus what makes wood desirable for the construction of homes, furniture, and fine cabinetry. Wood also serves to conduct water throughout the tree, and it is this function that can cause a lot of distress if not fully understood. By its nature, wood is hygroscopic – it loves water and will absorb as much as it can. The amount of water wood holds balances with the amount of water available in the surrounding environment. To keep this balance, wood continuously exchanges moisture with the air around it. Wood continues to balance its water content with its environment, even decades after it was harvested and shaped into its final form.
This interaction can create problems, because wood changes in size as its moisture content changes; it acts much like a sponge. As wood absorbs water, it swells in size. When water is driven out of it, it shrinks.
The relative humidity of the surrounding air determines the moisture content of wood. Relative humidity measures how much water vapor is in the air— wood will either absorb or give off water to balance. High humidity means high water vapor in the air thus, wood will naturally absorb this water. Low humidity means the air is dry and the air will pull water back out of the wood. Temperature plays a lesser role in the moisture content of wood.
Holiday Kitchens recommends that homeowners maintain a controlled temperature and humidity where their cabinetry is stored and installed:
Relative Humidity between 35 and 50 percent & Temperature between 60 and 90 degrees
Wood species has little effect on the moisture content – that is fairly constant for woods offered by Holiday Kitchens. The degree of shrinking and swelling is tied closely to the species of wood. For example, Red Oak can change in size more than Alder.
Wood does not expand or shrink equally in all directions due to the structure. Wood is composed of a complex network of fibers, cells, and microscopic tunnels – which we see as grain (Imagine tight bundles of tiny straws running the length of the tree). The microscopic tunnels in wood run in generally one direction from the bottom of the tree to its top to transport fluids through the tree.
Wood will mostly change in size across the grain while remaining relatively the same in the direction of the grain. As they swell, they grow wider, not longer; when they shrink they grow narrower, not shorter. This difference is important as it impacts the components of cabinetry.
Some fluctuations in temperature and humidity are bound to happen, and cabinet construction methods have been developed to compensate for this. Cabinet boxes at Holiday are built from either plywood or particle board (depending on your Holiday order) core materials which are specifically designed to resist changes in dimension due to moisture content changes.
Change in humidity for Contemporary (solid wood) doors will be uniform across the width of the entire face of the door which may change the overall width affecting the reveals on each side, but very little at the top or bottom. Whereas five piece doors (framed with a panel) are designed to move with humidity changes while maintaining their overall square shape and avoiding warping. If you look at the cross rails (the top and bottom pieces of the door), you will see that the grain runs across the door, whereas the grain in the panel and in the stiles (the left and right pieces of the frame) run up and down. The frame of the door is constructed with spacers in the groove to allow for reasonable changes in the width of the panel.
*If the moisture content gets too low, the panel will shrink and could expose edges of the panel that haven’t been finished. If the moisture content gets too high, the panel could expand beyond what the spacers in the frame can allow, causing the outer frame to crack.
In winter, the air is colder and can’t hold as much moisture so all wood products will dry out to some degree. In summer the air is warmer and holds much more moisture, causing wood to swell in response. Wood will always respond to the natural cycle temperature and humidity. This affects all wood in the home: the doors, the trim, the floors, the furniture, and the cabinetry. Holiday Kitchens designs its cabinetry to be able to adjust with these constantly cycling conditions. For example, joints in wood products will move slightly over time, and are designed to do just that so the wood itself is not damaged.
The effects of this natural cycling can be minimized by good temperature and humidity control in the home. Holiday Kitchens strongly recommends maintaining an environment with temperatures between 60º-90ºF and a relative humidity of 35-50%. These ranges recognize that there will be some natural cycling, but should prevent serious damage from occurring.
Failing to control wood’s moisture content is a leading cause of damage to cabinetry. Excessive changes in moisture content create tremendous stresses on your cabinetry as the wood grows or shrinks. The majority of cracks, splits, open joints, and other damage to cabinetry results from failing to maintain a steady range of temperature and humidity. Outside of Holiday’s recommended ranges, you risk seriously damaging your cabinetry.
Brief fluctuations in temperature or humidity, such as opening the door in winter or mopping your floor, will not adversely affect your wood cabinetry. Simple humidity and temperature control is the best way for you to ensure your Holiday Kitchen cabinetry lasts a lifetime.
CHART 1: Equilibrium Moisture Content of Wood
CHART 2: Expansion of Wood