Choosing Thermally Modified Radiata for a Renovation: What to Check First

Evaluating the Existing Substructure for Wall Applications

For exterior wall renovations, the condition of your existing substructure is critical. Thermally modified radiata siding requires a robust and level surface for proper installation and long-term performance. Begin by inspecting the framing or sheathing for any signs of rot, moisture damage, or instability. Any compromised areas should be repaired or replaced before new material is installed.

Consider the type of existing wall assembly. If you are replacing an older siding material, you may need to evaluate the entire wall system, including insulation, vapor barriers, and the presence of a rainscreen gap. Thermally modified radiata benefits from a well-ventilated rainscreen system, which helps manage moisture and extend the lifespan of the material. If your current assembly does not include one, this renovation may be an opportunity to upgrade.

Ensure that the existing wall can support the weight of the new cladding. While thermally modified radiata is not excessively heavy, verifying the structural integrity is a fundamental step for any renovation. Check for plumb and level surfaces; any significant deviations will need to be addressed to achieve the desired aesthetic with a clear-grained material like thermally modified radiata.

Assessing Decking Subframes and Supports

For decking renovations, the existing subframe, including joists and beams, must be in excellent condition. Inspect all structural components for rot, insect damage, or excessive deflection. Replace any compromised lumber to ensure a safe and stable foundation for your new thermally modified radiata decking. The improved stability of thermally modified wood means it responds less to moisture than unmodified material, but the underlying structure must still be sound.

Verify that the spacing of your existing joists aligns with the requirements for the chosen thermally modified radiata decking profile. Standard decking often requires specific joist spacing to prevent sagging and ensure proper load distribution. If your current joist spacing is too wide, you may need to add additional blocking or sister new joists to meet the necessary support requirements.

Consider drainage and ventilation beneath the deck. Good airflow helps prevent moisture buildup, which is beneficial for both the decking and the subframe. Ensure that the ground below the deck is properly graded and that there are no obstructions impeding air circulation.

Choosing the Right Thermally Modified Radiata Profile for Your Renovation

Thermally modified clear radiata is known for its clean, consistent grain and is available in several profiles suitable for various applications. Understanding these profiles is crucial for matching the material to your renovation's aesthetic and functional needs.

This profile is excellent for achieving continuous architectural lines.

For decking, "S4S E4E" (surfaced four sides, eased four edges) profiles are common. Available in 5/4 × 6 and 2 × 6 nominal sizes, these are suitable for creating a durable and stable walking surface. The 2 × 6 size can also be used for structural details where a more substantial look is desired.

Trim and moulding applications can utilize "S4S E4E" in various sizes, including 1 × 8, 1 × 12, and 2 × 6. These provide flexibility for coordinating details across different parts of your renovation project, allowing for a cohesive design.

Custom milling is also an option, offering flexibility to coordinate slats, trim, and field profiles to achieve a specific design vision. This can be particularly useful for unique architectural details or matching existing design elements.

A Renovation Example: Replacing Exterior Siding

Consider a hypothetical renovation of a 20-foot by 10-foot exterior wall, currently clad with worn-out cedar shingles. The goal is to replace the shingles with Thermally Modified Clear Radiata Nickel Gap siding to achieve a modern, clean aesthetic.

First, the existing cedar shingles and any deteriorated sheathing would be removed. An inspection reveals that the underlying wall studs are spaced at 16 inches on center, which is suitable for most siding applications. However, the original construction lacks a rainscreen gap. The renovation plan includes installing a new weather-resistive barrier and vertical furring strips (e.g., 3/4-inch thick) over the sheathing to create a ventilating rainscreen cavity.

To cover 200 square feet, approximately 437 linear feet of siding are needed (200 sq ft / 0.458 sq ft/linear ft). Accounting for cuts, waste, and starting/ending boards, it would be prudent to order at least 10-15% extra, bringing the total to around 480-500 linear feet. This ensures enough material for accurate cuts and minimizes delays if a board needs to be replaced.

Considering Material Compatibility and Finishing

Thermally modified radiata has a natural, consistent grain that can be left to weather to a silver-gray patina or finished with a transparent or semi-transparent stain to maintain its initial warm tone. When planning your renovation, consider how this material will interact visually with other existing or new materials, such as stone, stucco, or metal accents.

If you plan to apply a finish, ensure that the chosen product is compatible with thermally modified wood. Always follow the finish manufacturer's instructions for application, as proper preparation and curing are essential for durability. The improved stability of thermally modified radiata means it has a lower moisture response, which can be advantageous for finish longevity compared to unmodified wood.

For fasteners, select corrosion-resistant options appropriate for exterior use, such as stainless steel. These fasteners help prevent staining of the wood and ensure a secure, long-lasting installation. Pre-drilling may be necessary, especially near board ends, to prevent splitting.

Before you order

• Assess existing substructure for rot, damage, and stability.
• Verify existing joist spacing for decking applications meets new material requirements.
• Determine if a rainscreen system is needed or can be integrated for wall cladding.
• Select the appropriate thermally modified radiata profile (e.g., Nickel Gap for siding, S4S E4E for decking) for your project.
• Calculate the required material quantity, including waste factor, based on project dimensions.
• Consider the desired aesthetic: natural weathering or a specific finish.
• Confirm compatibility of chosen fasteners and finishes with thermally modified wood.
• Plan for proper ventilation and drainage in both wall and deck assemblies.

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

Keep planning your project