Scandinavian Thermally Modified Wood at the Base of a Wall: Clearance and Drainage

Why Ground Clearance Matters for Scandinavian Thermally Modified Wood

Scandinavian Thermally Modified Wood, while enhanced for stability, still benefits from proper installation practices that manage moisture. Direct contact with the ground or insufficient clearance can lead to several issues. These include prolonged exposure to standing water, which can encourage biological growth, or splash-back from rain, which can deposit dirt and accelerate surface weathering. Adequate clearance promotes airflow, allowing the material to dry efficiently after rain or humidity, which is crucial for any exterior wood product. It also helps prevent pests from accessing the wall assembly from the ground.

The heat and steam modification process improves the wood's resistance to moisture absorption and decay compared to untreated wood, making it suitable for exterior applications. However, no wood product is impervious to the effects of constant moisture exposure. Establishing a clear separation from the ground is a fundamental step in a durable facade design.

Standard Ground Clearance Recommendations

This measurement should be taken from the lowest point of the wood cladding to the highest point of the adjacent finished surface, whether that's soil, pavement, or another hardscape element. For areas prone to heavy rain, snow accumulation, or irrigation splash, a greater clearance may be prudent.

This clearance allows for effective drainage away from the wall and reduces the likelihood of moisture wicking up into the bottom edge of the cladding. It also provides space for routine maintenance around the building's perimeter without disturbing the cladding.

Considering Adjacent Surfaces and Drainage

The type of surface adjacent to your wall significantly impacts ground clearance planning. For softscapes like garden beds or lawns, ensure the finished grade slopes away from the foundation to prevent water pooling. For hardscapes such as patios, walkways, or driveways, confirm that these surfaces also shed water away from the building. The base of the cladding should always be above the highest anticipated water level, which includes splash-back during heavy rain.

Consider incorporating a gravel strip or a drainage channel at the base of the wall if direct runoff onto the cladding is a concern. This can further mitigate moisture exposure and keep the bottom edge of the Scandinavian Thermally Modified Wood drier. Proper rainscreen detailing, which includes a continuous air gap behind the cladding, is also essential for managing moisture within the wall assembly itself.

Worked Example: Planning Ground Clearance for a Facade

Imagine you are cladding a new garden shed with Scandinavian Thermally Modified Wood, using a V-Joint profile. The shed will sit on a concrete slab foundation that extends 4 inches above the surrounding finished soil grade. The proposed cladding will start at the top of the concrete slab.

Since your slab is already 4 inches above grade, you would install the first cladding board 2 inches above the top of the concrete slab. If the finished grade were a paved patio that sloped away, the same principle applies: measure from the highest point of the patio surface.

This approach ensures that the valuable Scandinavian Thermally Modified Wood, known for its "Nordic character with a more stable, consistent structure," is protected from excessive ground-level moisture, contributing to its longevity and appearance.

Integrating with Foundation and Flashing Details

The ground clearance works in conjunction with foundation waterproofing and flashing details. The bottom edge of the cladding should ideally terminate above any horizontal flashing that sheds water away from the foundation. This flashing, often called a Z-flashing or drip cap, directs water out and away from the wall assembly, preventing it from running down behind the cladding or into the foundation.

Ensure that the air gap of your rainscreen system, if used, is maintained at the base of the wall to allow for continuous airflow and drainage. The bottom of the rainscreen cavity should be open to the exterior, often with insect screening, to allow any accumulated moisture to escape and air to circulate. This complete system approach is vital for the long-term performance of your Scandinavian Thermally Modified Wood facade.

Before you order

• Confirm the finished grade level around the entire perimeter of the building.
• Measure the height of the foundation or base wall above the finished grade.
• Calculate the required offset for the first cladding board from the top of the foundation.
• Verify that the adjacent surfaces (soil, pavement) slope away from the building.
• Plan for any necessary drainage elements, such as gravel strips or channels.
• Ensure that foundation waterproofing and base flashing details integrate correctly with the cladding's starting point.
• Confirm the rainscreen air gap is maintained and vented at the base of the wall.

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