As cabinet professionals, we all deal with the same reality: wood is a living material that continues to respond to its environment long after installation. Through our years of manufacturing wood components, we've gathered insights about wood movement that we'd like to share with fellow professionals. This technical resource also includes a compilation of the best practices and information in the wood industry, including citations. The goal of this blog is to help you educate clients, set proper expectations, and demonstrate expertise when wood movement questions arise - ultimately reducing expensive service calls to completed projects.
Wood's behavior is defined by its hygroscopicity - its natural ability to absorb and release moisture to balance with the surrounding environment. This continuous exchange causes dimensional changes, even in kiln-dried lumber and finished wood products.
Think of wood like a sponge on a counter: when humidity is high, the sponge expands; when dry, it shrinks. Wood behaves similarly, though less dramatically. A 4-5% change in wood's moisture content leads to about a 1% change in size across the grain².
On a wide cabinet door, even that small percentage is enough to make gaps or rubbing noticeable.
Air has temperature and relative humidity. For woodworking, there's a third critical factor: equilibrium moisture content (EMC), which represents the moisture content wood seeks at given temperature and RH conditions¹.
Simply put, wood always tries to balance itself with the air around it. The point where wood and air "agree" with each other is called the equilibrium moisture content (EMC).
Most interior wood components (floors, cabinets, doors, furniture) are manufactured and installed at a moisture content that matches ~30-40% relative humidity.
At this range, wood stabilizes its EMC at around 6-8% — which minimizes shrinkage, swelling, cracks, and warping.
If RH is too low (<25%) = EMC (<5%) : Wood dries out → center panels shrink, assembly joints shift (creating small hairlines on painted 5-piece doors)
If RH is too high (>50-60%)= EMC (>10%): Wood swells → center panels expand and may push against stiles, doors may rub together
The single most important factor in a homeowner's control is the maintenance of a consistent indoor environment. Wood performs best when the relative humidity (RH) is stable. All warp occurs because the moisture content changed, and moisture changed because the relative humidity changed; temperature is not a factor, only relative humidity³.
Most seasonal movement issues occur when humidity swings dramatically between seasons:
If your wood components bow or warp slightly because of seasonal changes (slight gradual change over time), most often the wood components will come back to their original shape when the RH returns to the 35% range. Stated another way, slow, small moisture changes will not be a problem even with some slope of grain. Twist is worse when the moisture change is large and fast³.
However, wood has a limit to how much it can deform and return to its original shape. A rapid or extreme change in moisture content can generate internal stresses that exceed the wood's elastic limits, causing a lasting change to its cellular structure. This is known as "permanent set" or irreversible deformation. Once this occurs, the wood's internal "memory" of its original shape is lost. This is actually how we manufacture curved doors; the wood is exposed to extremely high humidity and then bent into shape.
If a client says: "2 doors are warped, they are defective" in a full kitchen, here's what's happening:
Typically, doors for one particular job are manufactured with wood from the same bundle: cut, dried, and milled at the same humidity levels. Even when all these conditions are met, the wood may present different internal structure. Wood's stability depends heavily on grain orientation. Boards with "slope of grain" - where fibers aren't perfectly parallel to the board's length - twist and warp more readily when moisture changes, even slightly³. Within the same order, one door may react more to humidity because a stile or rail has angled grain. This is not a manufacturing defect.
Also, it's possible that the 2 doors are within a "microclimate" - next to a dishwasher, for example.
The image above show why hairline cracks may appear. It shows the bottom left corner of a 5 piece door. The bottom 'rail' of the door have grain that runs left to right. The left 'stile' of the door have grain that runs top to bottom. The arrows show the direction in which the grain expand and contract. As you can see, the wood parts are expanding and contracting in opposite directions. The black line line that appears at the joint shows the stress of the paint. It is not the joint falling apart; the paint is not flexible enough to withstand the movement of the wood. Every component manufacturer and the greater majority of cabinet manufacturers will not cover this under warranty once the kicthen is installed.
Some clients may insist their humidity is perfectly controlled, saying something like: "There is actually an ERV with digital display that shows humidity levels, so I am certain that we adhered to your humidity recommendations."
In these situations, acknowledge their monitoring system while providing technical clarification. ERV systems (Energy Recovery Ventilators), also known as air exchangers, are not designed to remove high levels of air humidity. During heatwaves, they solely transfer humid air from outside to inside and can actually increase humidity levels in homes⁴.
Point out that ERV systems typically measure whole-house humidity, but localized conditions near heating vents, windows, or exterior walls create microclimates.
Remember: RH readings of 35% during installation and 35% on service calls does not mean humidity remained constant between visits - fluctuations between readings often cause the movement issues you're called back to address.
It is common practice to limit warranty regarding cabinetry and cabinetry components with regards to relative humidity after installation. Wood is a natural material that will move according to its environment.
Best practices include humidity-related waivers in your contracts with homeowners. You may include this citation:
"Even panels with ideal materials, construction, and processed according to best practices can cause problems when introduced to a highly variable environment"⁵.
Before discussing humidity management in your shop or for the homeowner, let's address a common misconception about the transit of wood components.
Some may speculate that wood components may be altered by spending 1,2 and even 5 days in transit , in varying humidity conditions.
At Caron, we have shipments crossing Canada and the US eastern seaboard every day, with scarcely any callbacks for warped components out of the package. The components are manufactured with wood at 6-8% MC as it comes in the plant, and as it leaves. We package the doors with up to 4 layers of protection ( plastic wrap, foam, 3 ply cardboard and a final cardboard). Such packaging creates a protective micro-environment, thus the components experience negligible internal moisture variations during transit. Furthermore, the flat stacking of components with foam in between prevents differential moisture absorption that may lead to warping.
When receiving and working on the components, make sure to keep humidity levels between 30 and 40%, all year round. We recommend always keeping the doors flat, stacked on top of each other, until they are ready for finishing. Putting doors upright on a wall may lead to warping or bowing.
If the doors are not pre-finished by our finishing department, we recommend applying finish in a timely manner. While wood movement cannot be stopped entirely, a quality finish can significantly help in controlling its pace and preventing uneven moisture absorption. A finish acts as a moisture retardant, slowing down the rate at which wood gains or loses water vapor. This allows the material to acclimate more gradually and evenly, reducing the stress that leads to warping³.
Plastering and drywall installation can spike indoor humidity to 80-85% RH according to industry studies. When delivering components during these phases, keep materials packaged and sealed to prevent moisture absorption⁶.
If possible, delay cabinet installation until construction humidity stabilizes. Use a digital hygrometer (under $40) and avoid installing when humidity exceeds 60% RH, as materials may absorb excess moisture causing post-installation movement⁶.
For doors affected by humidity fluctuations, you may consider these strategies:
As expert cabinet door manufacturers, we believe it is important to share tips about certain doors designs that are more prone to warping or cupping.
Certain door designs create inherent stability challenges due to uneven processing. When creating layouts for clients, we recommend considering smaller door sizes for these "higher-risk" designs.
Barn Wood Textures:
These rustic designs typically feature deep texturing on the face only, with the back of the door staying smooth. The manufacturing process involves a different treatment of the face than the back, creating tension in the door. Moreover, This creates uneven moisture absorption rates - the textured face has more surface area exposed to humidity changes while the back remains relatively sealed. The result is differential movement that may lead to warping in conditions where RH is not well maintained.
Reeded Panels:
Popular groove patterns require intensive milling of solid wood strips. The deep, closely-spaced channels remove significant material from one face while leaving the opposite side intact. This asymmetrical material removal creates internal stress and eliminates the natural balance in the wood structure, making cupping on tall and wide components more risky. Even when the 4" -inch- wide planks are glued to a more stable substrate ( like plywood), they will pull on the plywood if RH is not well maintained.
Deep relief designs on MDF one piece:
Even MDF may cup when intensively milled on one side. The removal of material and fiber disruption on one face creates an imbalanced structure that responds differently to moisture on each side. Any pattern requiring substantial material removal from one face disrupts the board's natural stress balance. Melamine backed MDF and adding more hinges will help keep the doors straight on the cabinet.
For all designs listed above, strategic hinge placement significantly improves performance with almost all of the warping or cupping that may happen. The typical rule of thumb of the industry is one hinge every 30 inches in height. Our experience shows 1 hinge every 20 inches provides optimal support for the products listed above: a door between 40 and 59 inches should have 3 hinges minimum.
Questions about wood species selection, moisture content specifications, or technical applications? Contact our technical team - we're happy to share insights from our manufacturing experience.
1-www.thisiscarpentry.com/2010/09/03/moisture-content-wood-movement/
2-www. mathscinotes.wordpress.com/2014/10/24/rule-of-thumb-for-wood-shrinkage
3-www.woodworkingnetwork.com/knowledge-center/wood-dr/why-does-cabinet-door-warp
4-www.pvhvac.com/blog/will-erv-dehumidify-home/
5-www.woodworkingnetwork.com/best-practices-guide/panel-processing/how-avoid-panel-warp-cabinets-and-furniture-projects
6-Kitchen Cabinet Manufacturers Association (KCMA) Installation Standards and Guidelines
7 -https://www.woodshopdiaries.com/how-to-fix-a-warped-cabinet-door/
