Posi Joists

What Are Posi Joists?

Posi-Joists, also known as Posi-joists or metal web joists, are a type of engineered floor and roof truss system used in construction. They are designed to combine the benefits of both traditional timber joists and engineered wood I-joists while addressing some of their limitations. Posi-Joists have become increasingly popular in residential and commercial construction due to their versatility and performance advantages. Here are some key features and characteristics of Posi-Joists:

The Benefits of Posi Joists

Composite Structure: Posi-Joists are made by sandwiching a lightweight steel or aluminum web between two layers of oriented strand board (OSB) or plywood. This combination of materials provides the benefits of strength and stability from the metal web and versatility from the wood panels.

Open Web Design: The open web design of Posi-Joists allows for easy installation of utilities like plumbing, electrical wiring, and HVAC ducts. This feature simplifies the process of running services through the floor or roof trusses, reducing the need for notching or drilling holes in the structural members.

Span Capabilities: Posi-Joists are engineered to offer longer clear spans than traditional timber joists, I-joists, or solid wood beams. This increased span capacity can result in more flexible and open building layouts, as well as reduced need for additional load-bearing supports.

Design Flexibility: Builders and architects have the flexibility to specify the depth, width, and spacing of Posi-Joists to meet the specific load and span requirements of a project. This customization allows for tailored designs that optimize structural efficiency.

Stability: The metal web in Posi-Joists provides excellent resistance to both deflection and twisting, ensuring a stable and level floor or roof structure.

Reduced Weight: Compared to traditional solid wood joists or beams, Posi-Joists are lighter, making them easier to handle during installation.

Cost-Effective: While the initial material cost of Posi-Joists may be higher than that of standard timber joists, their ability to reduce construction time, minimize material waste, and provide longer spans can lead to overall cost savings in a project.

Fire Resistance: The metal web in Posi-Joists can provide improved fire resistance compared to some other engineered wood products. However, fire protection measures are still recommended by local building codes and fire safety regulations.

Sustainability: Posi-Joists are considered environmentally friendly due to their efficient use of wood resources and the potential for sustainable steel or aluminium materials in the web. Additionally, the reduced waste during manufacturing can contribute to sustainability efforts.

Posi-Joists are commonly used in various types of construction, including residential, commercial, and industrial buildings, where they provide the benefits of both traditional timber and modern engineered systems. When considering the use of Posi-Joists in a project, it is essential to work with a structural engineer or architect to ensure proper design and installation in compliance with local building codes and regulations.

Are Posi-joists Stronger Than Timber?

Posi-Joists can be engineered to have specific strength characteristics tailored to the requirements of a project. In many cases, Posi-Joists can provide greater strength and load-carrying capacity compared to traditional sawn timber joists of the same size. This enhanced strength is due to the combination of materials in Posi-Joists, which typically include a steel or aluminium web and oriented strand board (OSB) or plywood flanges.

The combination of a metal web with wood flanges creates a composite structure that leverages the strength of both materials. The metal web provides excellent resistance to deflection and twisting, while the wood flanges contribute to the overall strength.

Posi-Joists are engineered to meet specific load and span requirements, allowing for optimization of the structural capacity. Engineers can design Posi-Joists to carry heavier loads and span longer distances than traditional timber joists.

While Posi-Joists can offer enhanced strength compared to traditional timber joists, it's important to note that the specific strength of Posi-Joists can vary depending on the design, materials used, and engineering specifications. Additionally, factors such as the intended use of the structure, local building codes, and safety regulations will influence the design and selection of the appropriate floor or roof system.

Do Posi Joists Need Noggins?

Posi-Joists typically do not require noggins or blocking between the joists in the same way that traditional solid timber joists do. The reason for this difference is the inherent design and construction of Posi-Joists.  The open-web design of Posi-Joists allows for easy installation of utilities such as plumbing, electrical wiring, and HVAC ducts within the joist spaces. This design feature eliminates the need for noggins or blocking to accommodate these services, as would be required in traditional timber joists.

What is The Dead Load of a Posi Joist?

The dead load that a Posi-Joist can support depends on various factors, including the specific design and dimensions of the Posi-Joist, as well as the materials used in its construction. Dead load refers to the static weight or permanent load that a structural element, such as a floor or roof system, must support. It includes the weight of the building materials, finishes, and any permanent fixtures.  Because the dead load capacity of Posi-Joists can vary widely depending on these factors, it's crucial to engage a structural engineer or architect to perform the necessary calculations and provide specific load-bearing data for your project. They can design the Posi-Joist system to meet the structural requirements of your building while ensuring it complies with local building codes and safety standards.