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Among various building materials, wood is increasingly favored by the construction industry due to its environmental advantages, including recyclability, negative carbon emissions, and energy efficiency. Modern wooden structures are becoming increasingly popular and are being adopted worldwide. However, many people remain skeptical about whether modern wooden structures can withstand the test of moisture, especially in rainy or humid areas. Can wooden structures maintain long-term durability?
Photo: Chongqing Yuanlu Community Center
The relationship between moisture and wood
When exposed to moisture, wood is primarily threatened by various wood-rotting fungi and insects such as termites. Consequently, many people mistakenly believe that water is wood's natural enemy. This is not the case. Wood buildings can also maintain long-term performance in rainy or humid locations. The key lies in understanding how to manage moisture when designing and constructing wood-based building products.
Wood with a moisture content of less than 19% is considered dry. Its properties are stable, and it resists deformation or chemical reactions. All modern timber structures undergo a drying process to minimize any volume changes. This wood, pre-dried to a moisture content below 19%, offers moisture resistance approximately 10 times greater than that of brick-concrete structures. Furthermore, wood regulates indoor humidity, making buildings more comfortable. During periods of high humidity, it absorbs moisture; during dry periods, it releases moisture into the air. Clearly, water and wood can coexist harmoniously.
Photo: Houseboats on the Fuchun River in Hangzhou, Zhejiang
Photo: Houseboats on the Fuchun River in Hangzhou, Zhejiang
4D principles of moisture-proofing in modern wooden structures
Moisture enters buildings primarily through rainwater infiltration, water vapor diffusion, and air leakage. Therefore, as long as proper moisture protection is implemented during the design and construction phases, wood can be a building material that performs well in all climates.
Figure: 4D principles for moisture-proofing of wooden structures
D eflection
The key to moisture-proofing lies in preventing moisture from accumulating in the gaps between structural components. Improper design and construction allow rainfall from outside or water vapor from within to enter these gaps. Deflection aims to divert rainwater away from the building surface, minimizing its potential for infiltration into the building envelope and interior. Key measures include designing roof overhangs and water collection devices. This design and construction method can prevent moisture from accumulating in the gaps between structural components, leading to problems such as mold and rot.
Drying
In order to prevent condensation from making wooden structures damp and providing living conditions for mold and wood-rotting fungi, air diaphragms can be set up on the building shell to prevent moisture from condensing for a long time through evaporation diffusion and air flow movement.
Drainage
Drainage is achieved through the design of sloped roofs and horizontal components, primarily including drainage layers, breather paper, and felt. This allows water to flow out of the house under gravity while preventing rainwater from entering the interior structure. Wrapping the building's outer shell in a layer of one-way breather paper effectively reduces water vapor movement caused by diffusion, making the timber structure both moisture-proof and breathable.
Figure: DuPont Tyvek breathing paper
Durability material
Where necessary, antiseptic wood is used to improve the durability of key components. Antiseptic wood uses chemical preservatives to prevent the wood from decaying by cutting off its food supply. Only when the preservatives are injected into the wood under high temperature, high pressure, and vacuum conditions, creating a permeable treatment, can the wood achieve its overall antiseptic properties.
Moisture-proofing affects the durability and comfort of buildings. With the further development of modern timber construction technology, accurate control of wood moisture content and the 4D principle of moisture-proofing have made it possible to implement modern timber structures in a variety of environments.
Photo: Qingcheng Mountain Wowserinxi Boutique Hot Spring Tree House Inn