7 factors that influence timber cladding’s durability outdoors 

Wood exposed to outdoor conditions faces constant expansion and contraction due to temperature changes. Freeze-thaw cycles, especially in colder climates, can cause moisture inside the wood to freeze and expand, leading to cracks and structural damage over time.

Solution? Look for thermally modified wood. Wood’s physical and chemical properties change during thermal modification. When it’s heated, the wood releases moisture and its chemical composition is transformed. It lowers the wood’s absorbency, meaning that exposure to moisture no longer causes it to swell as much. It also improves dimensional stability, so the wood expands and contracts less in outdoor conditions.

Frequent rain, snow, or consistently high humidity can saturate wood, increasing the risk of rot, mold, and fungal decay. Areas where water tends to pool or where airflow is restricted can accelerate this degradation.

When installing timber cladding or decking, ensure sufficient airflow behind the boards. Leave an air gap of at least 25 mm behind the boards to prevent moisture damage by allowing for vertical air flow.

UV rays break down lignin, a key component that holds wood fibers together. This leads to the graying of the wood surface. The process starts immediately after the products are installed and can take anything from a few months to a few years depending on the intensity of UV radiation and water exposure they’re subjected to.

Any color changes may be uneven. Each board ages in its own way, and different sides of a building’s façade will also age differently depending on the sun and rain they’re exposed to. 

To protect the wood, apply UV-resistant oils or finishes regularly. Also note that with thermally modified wood, the graying of the surface doesn’t affect its structural integrity. It’s rather just an aesthetic change due to exposure to sunlight.  

Wood in direct contact with soil is more likely to absorb moisture continuously, creating conditions for decay. Improper drainage or lack of spacing between boards can also trap water, causing even naturally durable wood to fail prematurely. 

So, elevate structures off the ground where possible and install with adequate spacing for water runoff. We advise leaving a gap of at least 300 mm between the ground and the cladding.  

In coastal environments, salt-laden air and water can be particularly harsh on wood, increasing moisture absorption and surface breakdown. Urban pollution may also accelerate wear and discoloration. Insect activity (e.g., termites, carpenter ants) and fungal presence in certain climates are additional biological threats to consider. 

Using naturally durable wood species or modified wood products that are resistant to decay and insect attack can be beneficial in coastal areas. 

Even highly durable wood can underperform if installed poorly. Incorrect fasteners, lack of sealing on end grains, or insufficient ventilation behind cladding can compromise the wood’s performance and lifespan.  

Make sure you maintain proper ventilation and drainage behind the boards and use corrosion-resistant fasteners like stainless steel to improve the timber cladding durability.  

Wood is a natural material and that is part of its charm. That also means durability is not a “set it and forget it” property. Without regular maintenance such as cleaning, resealing, and repairing minor damage, even the best wood materials will degrade faster than expected. 

Luckily, natural uncoated thermally modified wood does not require much special care. Thermory thermowood cladding boards are durable and remain weatherproof for decades, even in the most demanding climates. Just make sure you clean surfaces regularly to remove dirt and organic buildup.