In timber, how does moisture content affect modulus of elasticity (MOE)?

• A. Higher moisture increases MOE.
• B. Higher moisture reduces stiffness, lowering MOE.
• C. Moisture content has no effect on MOE.
• D. MOE increases with temperature regardless of moisture.

Answer: (B)

Moisture content directly affects stiffness in timber. Water molecules insert into the wood’s cell walls and interfere with the strong, rigid interactions of the cellulose-hemicellulose-lignin network. That plasticizing effect makes the wood less stiff, so the modulus of elasticity decreases as moisture increases. In other words, drier wood is stiffer (higher MOE), and drying it out raises MOE while wetter wood has a lower MOE.

This is why higher moisture reduces stiffness, lowering MOE. The other statements conflict with how water weakens the elastic response of timber or wrongly imply moisture has no effect or that MOE rises with temperature regardless of moisture.