Understanding the Moisture Performance of Wood

Presented by [ Presenter’sRon Anthony Name ] Please add relevant logo Disclaimer: This presentation was developed by a third party and is here not funded by WoodWorks or the Softwood Lumber Board.

Course Description

This session covers the effects of moisture on wood used in construction. It begins with a discussion of how wood responds to various forms of moisture (relative humidity and liquid water), and the science behind wood shrinkage, swelling, and factors affecting decay and insect attack. Focusing on the use of structural wood, discussion shifts to how different products respond to environmental conditions before and after installation, common moisture problems observed in the field, and design considerations and specifications that can improve the long-term performance of wood products in a structure. Learning Objectives Review the interaction between moisture and 1. wood as a building material.

Consider the effects of relative humidity and 2. liquid water on wood products before and after construction.

Examine common wood-moisture issues 3. observed in construction.

Discuss considerations for design and 4. specifications to reduce the impact of moisture on the performance of wood products.

Wood is a biological material

So what? Wood behavior is highly variable! It is that variability relative to use of wood in construction that we need to understand

Engineered wood products

• Plywood • Oriented strand board • Glued laminated timber • Laminated veneer lumber • Structural I-joists • CLT

Factors affecting wood performance

• Moisture content • Durability • Construction details • Maintenance Moisture content

Amount of water in the wood expressed as a percent

Equilibrium moisture content

Moisture content at which wood is in equilibrium with water vapor present in environment Equilibrium moisture content

• Depends upon relative humidity • Is always changing • Affects wood performance

Shrinkage and swelling

• Varies between species

• Is a function of change of moisture content

• Results in warp and checking

Checking and splitting

• Checking is a natural process of wood drying • Checking does not typically impact structural performance • Splits extend to two sides of a member How do you make wood last? How do you make wood last?

KEEP IT DRY!

Fungi and wood

•Food •Moisture •Oxygen •Temperature Molds, stains and mildew

• Molds and stains penetrate the surface of wood but do not reduce strength • Mildew grows on the surface of wood and paint and do not reduce strength

Decay fungi

•Degrades wood constituents •Results in reduction of material properties Insects and wood

•Borers tunnel through wood but do not eat it • Bore holes contain frass

•Termites digest wood • Bore holes are clean or contain pellets Durability •Natural durability due to extractives •Chemical preservatives •Remedial treatments •Finishes •Detailing

What goes in a specification related to moisture?

• Species • Moisture content • Grade • Treatment • Detailing • Finish Questions?

This concludes this portion of the American Institute of Architects Continuing Education Systems Course

Ron Anthony Anthony & Associates, Inc. [email protected]

This presentation was developed by a third party and is not funded by WoodWorks or the softwood lumber check-off.