Rough Treated Dimensional (RTD) plywood is a specialized engineered wood product designed for environments where standard materials would quickly fail. It is manufactured specifically to resist degradation from moisture and biological factors, making it distinct from common interior-grade panels. RTD plywood provides a durable solution for applications requiring long-term performance under demanding outdoor conditions.
Understanding Rough Treated Dimensional Plywood
The “Treated” component of RTD plywood refers to a process where liquid preservatives are forced deep into the wood fibers under high pressure inside a closed cylinder. This pressure treatment provides long-lasting resistance throughout the entire panel. Unlike standard interior-grade plywood, such as the common CDX variety, RTD panels are engineered to maintain structural stability even when subjected to repeated wetting and drying cycles.
The “Rough Dimensional” aspect indicates that the panels are often sold in common construction dimensions and may retain a slightly coarser surface texture compared to sanded products. Standard thicknesses generally align with conventional construction materials, including half-inch (12.7 mm), five-eighths inch (15.9 mm), and three-quarter inch (19.05 mm) sheets. These panels are typically available in the standard four-foot by eight-foot (1.22m x 2.44m) sizing, facilitating straightforward integration into framing systems.
Performance Characteristics and Limitations
The primary benefit of RTD plywood stems from its superior resistance to fungal decay, commonly known as rot. This decay involves the decomposition of wood cell walls by fungi. The pressure treatment saturates the wood with compounds toxic to these organisms, effectively halting the enzymatic breakdown process that leads to structural failure. This defense mechanism also extends to insect infestation, particularly subterranean termites, which are deterred by the chemical barriers established within the wood fibers.
The treatment process introduces limitations that must be managed during construction. The preservatives and water carrier significantly increase the panel’s moisture content, resulting in a notably heavier material immediately after purchase. This retained moisture means that as the plywood slowly acclimates and dries out, it is susceptible to movement, including potential warping, cupping, or shrinking across its dimensions.
The surface finish of RTD plywood is typically less refined than that of sanded or finished-grade panels, which can affect its suitability for visible or fine-finish applications. Furthermore, the chemical components of the treatment can sometimes react with certain metals, necessitating specialized fasteners to prevent premature corrosion. The increased density from the treatment also means the material is more resistant to cutting and dulls saw blades faster than untreated material.
Ideal Projects for RTD Plywood
RTD plywood is optimally deployed in construction scenarios where the material faces consistent, prolonged exposure to moisture, high humidity, or direct contact with soil.
Outdoor Subflooring
One of the most common uses is for the subflooring of outdoor structures, such as utility sheds, small storage buildings, and playhouses. Using treated plywood for the floor deck ensures that ground moisture wicking up through the foundation or incidental rain runoff does not compromise the structure’s base over time.
Fencing and Skirting
The material is well-suited for constructing components of outdoor fencing or privacy walls, particularly the lower sections near the ground line. Where standard plywood or lumber would quickly absorb moisture and begin to rot, the treated panels maintain their integrity, extending the service life of the entire fence system. Using RTD plywood for skirting or lower wall panels provides a necessary moisture barrier.
Agricultural Structures
Another application involves agricultural and gardening structures, such as raised garden beds and planters, where the wood is in continuous contact with damp soil. The preservative treatment prevents the biological degradation that would rapidly occur in untreated wood, ensuring the beds remain structurally sound for many growing seasons. This direct contact with organic matter and moisture is where the material’s resistance truly proves its value.
Humid Interior Storage
RTD plywood provides a durable solution for utility and storage shelving installed in inherently humid or damp interior spaces, such as crawl spaces, unfinished basements, or enclosed porches. In these environments, airborne moisture and condensation often promote mold and mildew growth on standard wood products. Utilizing the treated panels for these storage systems prevents the wood from becoming a host for biological contaminants and maintains the integrity of stored items. The material is also often used for temporary exterior site hoardings or construction barriers that must withstand prolonged weather exposure.
Installation and Safety Requirements
Working with RTD plywood requires specific construction practices to ensure the longevity of the project and the safety of the installer. Due to the chemical nature of the preservatives, specialized fasteners are required to prevent premature corrosion, a process known as galvanic action. Installers must exclusively use hot-dip galvanized, stainless steel, or polymer-coated screws and nails, as standard fasteners quickly degrade when in contact with the treated wood.
Maintaining the integrity of the protective envelope is achieved by applying a topical preservative to any surface that has been cut, notched, or drilled. When the panel is cut, the internal treated layer is exposed, creating a potential entry point for moisture and decay organisms. Applying a brush-on end-cut sealant restores the protective barrier, preventing localized failure at the point of modification. This step is important for areas exposed to direct weather or ground contact.
Installers should take precautions when cutting or sanding the material because these actions release fine sawdust containing the preservative chemicals. Wearing a dust mask or respirator, along with gloves and eye protection, is necessary to minimize inhalation and skin contact. Once installed and fully dry, the material can be finished with exterior-grade stains or paints, though manufacturers often recommend a short curing period before application.