The landscape of rot-resistant lumber has changed dramatically since the Environmental Protection Agency phased out chromated copper arsenate (CCA) for residential use in 2004. In the years following that ban, the treated-wood industry introduced alkaline copper quat (ACQ) and copper azole (CA) as replacements. While effective at preventing rot and insect damage, these copper-based treatments proved significantly more corrosive to metal fasteners and connectors than CCA had been, forcing builders to switch to stainless steel or hot-dipped galvanized hardware at considerable expense. Now, a new generation of wood preservative treatments promises to combine the environmental benefits of modern chemistry with improved compatibility with standard building materials. For more detailed information, see harvesting and using your. For more detailed information, see wood plastic composites.
MicroPro: Fine Copper Particle Technology
The most widely available of the new treatments is MicroPro, developed by Osmose and licensed to multiple lumber producers under brand names including SmartSense, ProWood Micro, YellaWood MCQ, and MicroPro AC2 (available at Menards). MicroPro uses copper as its preservative agent, but in micronized particles rather than dissolved copper ions. This distinction is critical: the copper particles are so fine — measured in micrometers — that they are as effective as dissolved copper at preventing fungal decay and insect attack, but they are significantly less corrosive to metal fasteners.
The Micronized copper technology works by embedding microscopic copper particles deep into the wood cell structure during the pressure-treatment process. These particles release copper ions slowly over time, providing long-term protection against decay fungi and wood-boring insects. Because the copper is present as solid particles rather than dissolved ions, the electrical conductivity of the treated wood is much lower than that of ACQ or CA treated wood. This reduced conductivity translates directly to reduced galvanic corrosion of nails, screws, joist hangers, and other metal hardware.
In corrosion testing, MicroPro-treated wood has been shown to be no more corrosive than CCA-treated wood, making it safe for use with standard galvanized fasteners and connectors. This is a significant economic advantage for builders, as the premium for stainless steel hardware can add hundreds or even thousands of dollars to the cost of a deck or other outdoor structure. MicroPro is approved for above-ground, ground-contact, freshwater immersion, and saltwater splash applications, making it suitable for a wide range of projects from residential decks to marine structures.
Availability of MicroPro-treated lumber is currently strongest east of the Rocky Mountains, and the price is comparable to ACQ and CA treated lumber. As production capacity increases, availability is expected to expand nationwide.
Wolmanized L3: A Copper-Free Alternative
Arch Wood Protection, the manufacturer of the well-known Wolmanized brand, has taken a fundamentally different approach with its Wolmanized L3 Outdoor Wood treatment. Rather than relying on copper compounds, L3 uses a proprietary combination of fungicides, insecticides, and water repellents to protect the wood. Because there is no copper in the formulation, corrosion of metal fasteners is not a concern. Builders can use standard galvanized hardware without any special precautions.
The active ingredients in L3 are selected for their efficacy against a broad spectrum of decay fungi and wood-destroying insects, including termites and carpenter ants. The water repellents added to the formulation help the wood resist moisture absorption, which reduces the tendency of treated wood to crack, split, and cup as it dries. This dimensional stability is a practical advantage on the job site, as the lumber is less likely to warp or twist after installation.
According to Arch Wood Protection, the durability of L3 is comparable to traditional copper-based treatments, based on seven years of testing in above-ground applications. The treatment is currently approved for above-ground use only, meaning it should not be used in direct contact with soil or in applications where the wood will be continuously exposed to moisture. For deck boards, railings, fence boards, and other above-ground components, L3 provides effective protection without the corrosion concerns associated with copper treatments.
The price of Wolmanized L3 is comparable to ACQ and CA treated lumber, and availability is currently limited. As production ramps up, it is expected to become more widely available through major lumber retailers.
PureWood: A Non-Chemical Heat Treatment Process
The most innovative approach to rot-resistant wood comes from Bay Tree Technologies, whose PureWood treatment relies on heat and steam rather than chemical preservatives. The PureWood process involves heating wood to high temperatures in a controlled steam environment, which chemically changes the composition of the sugars and other nutrients in the wood cell structure. These sugars are converted into a non-edible substance that mold, fungus, and insects cannot digest, making the wood effectively immune to biological attack without the introduction of any biocides.
The thermal modification process also reduces the wood’s equilibrium moisture content, making it more dimensionally stable and less prone to swelling, shrinking, and checking. The wood darkens in color, developing a rich, warm tone similar to tropical hardwoods. This aesthetic change is often considered desirable for decking, siding, and other visible applications. For more detailed information, see composite decking.
PureWood has a 10-year track record in European markets, where it has been used in structural applications meeting European standards. The product is still in the process of being recognized by the International Code Council (ICC) for use in US construction, which has limited its distribution in the American market. Once ICC approval is obtained, PureWood is expected to be available through specialty lumber dealers. For more detailed information, see timber for construction.
The price of PureWood has yet to be determined for the US market, but it is expected to be competitive with premium treated-wood products. The treatment is approved for above-ground, ground-contact, freshwater immersion, and saltwater immersion applications, making it one of the most versatile options available.
Practical Implications for Builders
For builders and contractors, the emergence of these new treatment technologies has several practical implications. The most immediate benefit is the ability to use standard galvanized fasteners and connectors with MicroPro and L3 treated lumber, eliminating the cost premium associated with stainless steel hardware. On a typical 500-square-foot deck, the savings on fasteners and connectors alone can range from $200 to $500 or more, depending on the complexity of the structure.
The availability of multiple treatment options also gives builders flexibility in specifying materials for different applications. For ground-contact or high-moisture applications, copper-based treatments like MicroPro provide proven protection. For above-ground applications where corrosion is a concern, L3 offers effective protection without copper. For environmentally sensitive projects, PureWood provides chemical-free protection that meets the highest sustainability standards.
It is important to note that all treated lumber requires proper handling and installation practices to achieve optimal performance. End cuts should be field-treated with a compatible preservative to maintain protection where the treatment envelope has been breached. Fastener compatibility should be verified with the treatment manufacturer’s recommendations. Proper spacing and drainage should be provided to minimize moisture accumulation. And all treated wood should be installed in accordance with local building codes and manufacturer instructions.
Environmental Considerations
The transition from CCA to modern preservative treatments has significantly reduced the environmental impact of treated lumber. CCA contained arsenic, a known carcinogen that could leach into soil and groundwater. The new treatments — including MicroPro, Wolmanized L3, and PureWood — are formulated to be more environmentally benign, with no arsenic and lower toxicity profiles.
MicroPro’s micronized copper technology uses less copper overall than traditional dissolved-copper treatments, reducing the environmental footprint of the treatment process. L3 eliminates copper entirely, relying on organic biocides that break down more readily in the environment. PureWood uses no biocides at all, qualifying as a truly green building material that can be disposed of as untreated wood at the end of its service life.
For builders pursuing green building certifications such as LEED or the National Green Building Standard, the availability of these environmentally improved treated-wood products provides additional options for meeting sustainability criteria without compromising on durability or performance.
Conclusion
The treated-wood industry has come a long way since the phase-out of CCA, and the latest generation of preservative treatments offers meaningful improvements in corrosion resistance, environmental profile, and performance. MicroPro’s micronized copper technology restores compatibility with standard galvanized hardware while maintaining effective decay protection. Wolmanized L3 eliminates corrosion concerns entirely through a copper-free formulation. PureWood’s thermal modification process provides chemical-free protection with enhanced dimensional stability. Together, these technologies give builders and homeowners more choices than ever for rot-resistant lumber that meets their specific needs for durability, cost, and environmental responsibility.
Understanding Pressure Treatment Processes
The pressure treatment process is critical to the performance and longevity of rot-resistant wood. In a typical pressure treatment cycle, lumber is placed in a large cylindrical vessel called a retort. Air is evacuated from the retort to create a vacuum that draws moisture out of the wood cells. The preservative solution is then introduced into the retort under high pressure, forcing the treatment chemicals deep into the wood’s cellular structure. The amount of preservative retained in the wood, measured in pounds per cubic foot, determines the level of protection and the approved application category.
For above-ground applications, such as deck boards, railings, and fence pickets, a retention level of 0.25 pounds per cubic foot is typically sufficient. For ground-contact applications, such as fence posts, retaining wall timbers, and landscape edging, a higher retention level of 0.40 pounds per cubic foot or more is required. For permanent wood foundations and saltwater immersion applications, the highest retention levels are specified. The treatment process typically adds 10 to 20 percent to the cost of the lumber, which is a small premium compared to the cost of replacing untreated wood that has been damaged by rot or insect infestation.
Best Practices for Working with Treated Lumber
When working with any type of treated lumber, certain best practices should be followed to ensure optimal performance and safety. Always wear gloves, long sleeves, and eye protection when handling treated lumber, as the treatment chemicals can irritate the skin and eyes. Cut treated lumber outdoors or in well-ventilated areas to avoid inhaling sawdust. Wear a dust mask when cutting, as the fine particles can be irritating. Dispose of treated lumber scraps and sawdust in accordance with local regulations; do not burn treated lumber, as the smoke contains toxic compounds.
All cuts made on treated lumber should be field-treated with a preservative end-cut solution to maintain the protection envelope. The exposed end grain is the most vulnerable part of the treated wood, as it absorbs moisture more readily than the face grain. Apply the end-cut solution liberally to all cut ends, allowing it to penetrate before installing the board. Most manufacturers of treated lumber offer compatible end-cut solutions, or a general-purpose copper-based wood preservative can be used.
Fastener selection is critical when working with treated lumber. Even with the less corrosive MicroPro and L3 treatments, it is advisable to use hot-dipped galvanized or stainless steel fasteners for maximum corrosion resistance. Standard electroplated galvanized fasteners may corrode over time, particularly in wet or coastal environments. Use joist hangers and connectors that are rated for use with treated lumber, and check the manufacturer’s specifications for fastener compatibility before installation.
Deck Design Considerations for Longevity
Proper deck design is as important as material selection for achieving long-term durability. Provide adequate ventilation beneath the deck to allow moisture to evaporate. This means maintaining at least 18 inches of clearance between the ground and the bottom of the joists in most climates, and ensuring that the area around the deck is graded to drain water away from the structure. Use flashing tape on top of the joists to protect the wood from moisture trapped between the joists and the deck boards. Leave proper spacing between deck boards for drainage and airflow. Avoid trapping moisture against the house by maintaining a gap between the deck structure and the siding, and by using proper flashing where the deck ledger attaches to the house.