Standard Specifications for Grades of California Redwood Lumber

Above-ground redwood.

When a homeowner decides to use wood in a home project, durability and appearance are two important characteristics. Any type of exposed wood can decay or become infested with termites, but some wood varieties are more resilient than others. Redwood native to California is one type of these varieties, and it has a natural resistance to harsh weather and insects. But the quality of the redwood may vary from tree to tree, so a grading system has been developed to ensure quality.

Grading Factors

The quality of appearance of Californian redwood is determined by its clearness, or the number of knots in the piece. The fewer knots a piece has, the higher its appearance grade will be. Another factor in quality of appearance is the presence of surface defects that come in manufacturing. Redwood durability is determined by its ability to resist weather and insects, and this comes from the wood's color. The inner part of the tree, which is a reddish-brown, is most resistant to weather.

Types

Cal Redwood lists two types of main redwood grades: garden and architectural. Within both categories, further criteria for grading are whether the wood sample is heartwood, sapwood, a mixture of heartwood and sapwood, common, or clear.

Garden Grade

The subcategories for the garden grade are heartwood and heartwood/sapwood (a mixture of the two types). The heartwood type has two further divisions, construction and merchantable. Construction heart is used in areas such as decks, fences, and walls where there is possible contact with water, soil and insects. Merchantable heart is the economical version of construction heart and is used in similar situations. Heartwood/sapwood also has the divisions of construction and merchantable, which contain some less resilient sapwood and are not used where there is a potential for weather or insect contact.

Architectural Grades

The architectural grade also has all heartwood and heartwood/sapwood, as the two main categories. All heartwood is divided into clear heart and heart B. Clear heart has a low-blemish surface and is used on indoor woodwork. Heart B is also used on indoor woodwork, but has more surface blemishes than clear heart. The heartwood/sapwood category is divided into clear and B-grade. The clear grade is similar to clear heart, but contains some sapwood. B-grade also contains some sapwood, and has more knots than the clear grade.

Considerations

Grades containing sapwood are not generally used on any area that will be exposed, like cabinet faces, wall molding or trim. But, when considering a small-budget build, the lower grades can be used on anyarea and still have a quality appearance, as long as only that grade is used in those areas, creating uniformity.

References

• Cal Redwood: Grades and Uses
• Redwood Inspection: Grades
• California Redwood Information
• Redwood Lumber Grades and Uses (pdf)