The question of whether you put cement board under cabinets arises most often during a kitchen renovation, specifically when the existing surface is pressed wood, particle board, or any material that lacks the necessary structural integrity or moisture resistance. Before removing the old countertops and appliances, it is essential to evaluate the subfloor that will support the new cabinetry, as this decision dictates the longevity and stability of your entire installation. Cement board, also known as backer board or hardie board, is a dense, fibrous material typically used as a tile backing, but its application beneath cabinetry is a topic of significant debate within the contracting community.
Understanding the Purpose of Cement Board
Cement board is valued for its ability to provide a stable, flat, and moisture-resistant substrate where standard wood subfloors might fail. Unlike plywood, which can swell and delaminate when exposed to water leaks, cementboard resists rot and mold, making it an ideal surface for areas prone to humidity. When you put cement board under cabinets, you are essentially creating a fortress against the elements, particularly in environments where sinks are prone to overflow or splashes are frequent. This layer acts as a protective barrier, safeguarding the expensive hardwood or laminate flooring underneath from potential water damage that could occur over time from minor spills or condensation.
Structural Integrity and Weight Bearing
One of the primary reasons to install cement board is to address the issue of softness or flex in the existing floor. If the current subfloor feels springy or bounces when you step in the center of the room, the weight of heavy stone countertops and tall stock cabinets can cause noticeable deflection over time. By screwing the cement board into the joists and then securing the cabinets into the board, you distribute the weight more evenly across a rigid surface. This prevents the cabinets from sagging or the countertops from cracking due to an uneven support structure, ensuring that the installation meets professional standards for durability.
When is it Necessary?
You do not always need to install cement board if the existing floor is solid wood or plywood in good condition. However, if you are removing the old flooring to install new tile, or if the current surface is damaged, cement board becomes a necessary component of the assembly. It is specifically required if your local building code mandates a non-combustible, moisture-resistant barrier in the wet areas of the kitchen. In these scenarios, placing the cement board provides compliance with safety regulations and offers peace of mind regarding fire resistance and waterproofing, effectively future-proofing the kitchen against a significant portion of moisture-related failures.
Addressing Uneven Floors
Many older homes suffer from uneven floors, which can translate to uneven cabinets and gaps in the countertops. If you look across the floor and see gaps beneath the feet of the cabinets, simply shimming the cabinets is a temporary fix that does not solve the underlying problem. By grinding down high spots and building up low spots with a cement board overlay, you create a level plane that allows for a precise installation. This ensures that the cabinets sit flush, the counters align correctly, and the doors operate smoothly, which is critical for the aesthetic and functional success of the renovation.
Installation Considerations and Challenges
While the benefits are clear, the process of installing cement board under cabinets requires careful planning and execution. The material is heavy and dusty to cut, requiring appropriate safety gear and tools. Furthermore, you must account for the height difference; cement board adds approximately a quarter-inch to half-inch of elevation to the floor. This transition must be managed where the kitchen meets the adjacent hallway or dining room to avoid a tripping hazard. Professional installers often use a thinset mortar to bed the cement board, followed by proper fastening with screws spaced every six inches to ensure a tight, secure bond that prevents movement.
Alternative Solutions
Depending on the specific conditions of your project, there are alternatives to full cement board overlay. If the goal is merely to protect against minor spills and the existing floor is structurally sound, a high-quality moisture barrier paint or a sheet of plywood sealed with urethane might suffice. That said, if you are installing large-format tiles or solid surface materials that require extreme rigidity, cement board is often the industry-standard recommendation. Evaluating the scope of the work—whether you are refreshing the look or performing a complete gut—will determine if the added labor and material cost is justified for your specific situation.
Final Verdict for Homeowners
Deciding whether you put cement board under cabinets is ultimately a risk management strategy. For the homeowner planning to stay in the house for decades, the investment pays off in durability and resistance to water damage. For a flipper focused on a quick turn, the answer may lean toward a simpler solution to meet code and provide a functional surface. By assessing the current condition of the subfloor, the type of materials being installed, and the environmental factors of the space, you can determine if this step is essential for a successful, long-lasting kitchen transformation.
