What Supports Thermally Modified Wood? Plan the Substructure

Understanding the Role of the Substructure

The substructure for thermally modified wood cladding serves several vital functions. Primarily, it creates a flat, plumb, and stable surface for attaching the cladding. It also establishes an air gap, which is crucial for ventilation and moisture management, especially in exterior rainscreen applications. This air gap allows any moisture that penetrates the cladding to drain away and promotes drying of the wall assembly.

For exterior applications, the substructure often works in conjunction with a weather-resistive barrier (WRB) and continuous insulation, forming a comprehensive wall system. The specific design of the substructure will vary based on the cladding profile, the intended application (interior or exterior), and local building practices.

Furring: Creating the Air Gap and Fixing Points

Furring strips, also known as battens, are typically the primary components of the substructure. They are installed over the structural sheathing or masonry and provide the necessary spacing for ventilation and the attachment surface for the cladding.

For horizontally installed cladding, vertical furring strips are common to ensure drainage and airflow. For vertically installed cladding, horizontal furring strips are used, often with counter-furring (vertical furring over horizontal furring) to maintain a continuous drainage plane and ventilation gap.

The dimensions and material of the furring strips are important. Wood furring is common, but metal furring systems are also available. The spacing of the furring strips must align with the specified fastener spacing for the thermally modified wood cladding, ensuring each piece is adequately supported.

Fixing Methods: Securing Cladding to Substructure

The choice of fixing method directly influences the substructure design. Thermally modified wood cladding can be installed using visible fasteners or concealed fastening systems. Visible fasteners, such as screws or nails, penetrate the face of the board and secure it directly to the furring. This method requires careful planning to ensure fasteners are consistently aligned and appropriately sized for the cladding thickness and furring material.

Concealed fastening systems, often clips or hidden screws, attach to the back or edge of the cladding board and then to the furring. These systems require specific furring dimensions or profiles to accommodate the clips. They are generally preferred for a clean, uninterrupted aesthetic. Regardless of the method, fasteners must be corrosion-resistant and compatible with the thermally modified wood to prevent staining or degradation.

Substrate Considerations: What's Behind the Furring?

The substrate is the underlying material to which the furring strips are attached. This could be structural sheathing (e.g., plywood, OSB), concrete, masonry, or existing framing. The substrate must be sound, stable, and capable of securely holding the fasteners that attach the furring. For exterior applications, the substrate often includes a weather-resistive barrier (WRB) applied before the furring to protect the wall assembly from moisture.

When dealing with renovation projects, assessing the existing substrate's condition is crucial. Any deteriorated or unstable sections must be repaired or replaced before installing the new substructure. For new construction, ensure the substrate is properly prepared and meets all structural requirements.

Worked Example: Planning a Horizontal Cladding Substructure

Consider a hypothetical exterior wall measuring 10 feet high by 20 feet wide that will receive horizontal thermally modified wood cladding.

1. **Determine Furring Orientation:** For horizontal cladding, vertical furring strips are needed to provide a continuous drainage plane and attachment points.

This means roughly 11 vertical furring strips (20 feet / 2 feet = 10; plus one for the end) will be needed, each 10 feet long.

These strips will be securely fastened through the WRB into the structural studs or sheathing.

If using a concealed clip system, verify the clip's requirements for furring width and depth.

This example simplifies the process; actual projects require detailed drawings, consideration of window/door openings, and corner details. Always consult manufacturer guidelines for specific product recommendations.

Related products for a complete system:

NORX Thermally Modified Wood Cladding: [https://www.lumberplus.com/brands/norx]

Maximo Accoya Siding: [https://www.lumberplus.com/products/maximo-accoya]

Siding and Cladding Options: [https://www.lumberplus.com/siding-and-cladding]

Before you order

• Confirm cladding profile and required fastener spacing.
• Determine cladding orientation (horizontal or vertical).
• Select furring material and dimensions (e.g., wood, metal, thickness for air gap).
• Plan furring orientation and spacing based on cladding and structural support.
• Choose appropriate fasteners (visible or concealed) and ensure compatibility.
• Assess existing substrate for stability and flatness, or plan for new substrate.
• Integrate weather-resistive barrier and any insulation into the wall assembly.
• Detail around openings, corners, and transitions.
• Verify local building code requirements for ventilation and attachment.

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

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