Our WPC solid joists are available in 40*25mm and 40*30mm specifications, serving as high-strength foundational support structures specifically designed for outdoor decking and wall systems. Unlike traditional hollow joists or rot-prone treated timber, these joists utilize a fully solid extrusion process with extremely high density. They offer exceptional compressive strength, bending resistance, and screw-holding power, stably supporting the boards above without sagging or deforming under prolonged foot traffic. Furthermore, they are completely waterproof, rot-proof, insect-resistant, and termite-proof, withstanding underground moisture or rain immersion to fundamentally extend the lifespan of the entire decking system. The 40*25mm size is ideal for standard residential patios, balconies, and lightweight wall panel installations, while the heavier-duty 40*30mm is better suited for high-load public areas such as park boardwalks and commercial plazas, providing a safe, stable, and maintenance-free understructure.