Redwood lumber arrives at the lumberyard in more than 30 grades, from general-purpose boards to highly specialized stock intended for a single use. The grade stamped on the board controls both appearance and durability, and it directly affects what the wood costs and where it should be used. Builders who understand the grading system can match material to application instead of overpaying for clear heart on a fence that only needs construction grade. The same logic applies to concrete, where the grades of ordinary Portland cement determine mix design and strength.
This article explains how redwood gets its grades, what the architectural and garden groupings mean, and how to choose the right grade for decks, siding, fences, and structural work.
How Redwood Lumber Gets Its Grades
Redwood is graded by appearance and durability, with criteria defined by the Redwood Inspection Service and now administered by the Western Wood Products Association. The grade depends on where the board was cut in the tree trunk, how old the tree was, how the wood developed, and the direction of the cut. Two primary groupings cover the full range: Architectural and Appearance grades for visible work, and Garden and Structural grades for outdoor and load-bearing use. Each grouping splits further by whether the wood came from heartwood or sapwood.
A parallel structure exists in other building materials. Cement grades and standards, for example, organize products by strength and composition the way lumber grades organize boards by appearance and durability.
Heartwood vs. Sapwood
Heartwood is the older, inner part of the trunk. It contains natural extractives that make redwood resistant to decay and insects, and it carries the rich reddish color the species is known for. Sapwood is the outer layer that transports water; it is paler, softer, and less durable. Boards cut entirely from heartwood earn the premium grades, while boards with sapwood fall into the common grades.
Where the Board Comes From
A board cut from the center of a large old-growth trunk can be clear heart on both faces. The same species grown fast on a young plantation yields narrower, knottier boards that grade much lower. Growth rate and harvest age show up directly in the grade stamp, which is why two boards that look similar can be priced very differently.
Architectural Grades for Visible Work
Architectural grades are chosen when the wood will be seen and judged: siding, paneling, cabinetry, millwork, and outdoor structures where appearance counts. The five primary architectural grades step down in quality from Clear All Heart to B Grade.
What Clear All Heart Actually Means
Clear All Heart is the finest architectural heartwood grade. It is typically certified kiln dried, well manufactured, and free of defects on at least one face, and it comes surfaced or saw-textured. Heart Clear allows limited imperfections; Heart B permits a few knots and characteristics not allowed in the clearer grades. Sapwood Clear carries the same general quality as the heart grades but contains sapwood in varying amounts, and B Grade allows limited knots and other imperfections.
| Grade | Heartwood or sapwood | Typical characteristics | Common uses |
|---|---|---|---|
| Clear All Heart | Heartwood | Free of defects on at least one face; kiln dried | Siding, paneling, cabinetry, millwork |
| Heart Clear | Heartwood | High quality with limited imperfections | Siding, paneling |
| Heart B | Heartwood | Few knots and other characteristics allowed | Siding, outdoor structures |
| Sapwood Clear | Mixed | Sapwood in varying amounts | Siding, paneling |
| B Grade | Mixed | Limited knots and imperfections | General appearance work |
Grading by appearance works the same way in other materials. Concrete is sorted into grades of concrete by strength and mix proportions, and picking the wrong one is just as costly as ordering the wrong lumber grade.
Garden and Structural Grades for Outdoor Work
Garden grades trade appearance for economy. They are built for decks, posts, retaining walls, fences, and garden structures where knots and slight imperfections do not matter. Construction Heart contains knots of varying sizes and other slight imperfections; Merchantable Heart is the economical option with larger knots, checks, splits, and some manufacturing flaws. On the sapwood side, Construction Common mixes heartwood and sapwood, and Merchantable adds sapwood in varying amounts to the same general quality.
Strength-Graded Deck Options
Deck Heart and Deck Common are the two grades that add strength grading. They look similar to Construction Heart and Construction Common but are tested for structural performance and available only in 2×4 and 2×6 sizes. When a deck joist or beam must carry load, the strength-graded stock is the safe choice. Foundations rely on the same idea, where the different grades of concrete determine how much load a footing can carry.
| Grade | Heartwood or sapwood | Characteristics | Typical uses |
|---|---|---|---|
| Construction Heart | Heartwood | Knots of varying sizes, slight imperfections | Decks, posts, retaining walls, fences |
| Deck Heart | Heartwood | Strength graded; 2×4 and 2×6 only | Decks |
| Merchantable Heart | Heartwood | Larger knots, checks, splits | Fences, retaining walls, garden structures |
| Construction Common | Mixed | Heartwood and sapwood | Decks, fences, above-ground garden use |
| Deck Common | Mixed | Strength graded; 2×4 and 2×6 only | Decks |
| Merchantable | Mixed | Sapwood in varying amounts | Fences, rails, above-ground outdoor use |
The unseasoned garden grades are the workhorses of exterior construction. They carry the loads, shrug off weather, and keep the project budget in range while the premium grades go where they will be seen.
Choosing the Right Grade for the Job
The right grade balances three things: how visible the wood will be, how much load it will carry, and how much contact it will have with soil and weather. A privacy fence needs durability at the ground line but can carry knots above it. A living room ceiling needs clear faces and stable, kiln-dried stock.
For weathered installations, the starting condition of the wood determines what restoration takes. Boards that have grayed and checked can still be brought back, and the steps for cleaning and staining weathered redwood siding apply to most exterior redwood that has been left unfinished.
A Selection Checklist by Application
- Identify the exposure: ground contact, weather-exposed, or interior
- Determine the load path: deck joists and beams need strength-graded stock
- Decide how visible the finished work will be
- Compare grade prices against the cost of replacing a failed board
- Order kiln-dried stock for interior work and anything that must stay flat
When Premium Grades Pay Off
Clear All Heart earns its premium where replacement is expensive: custom millwork, paneling in occupied rooms, and siding that would take days to swap. In a fence, the same money buys more footage of Construction Common.
Buying, Storing, and Working With Redwood
Redwood arrives seasoned or unseasoned, surfaced or rough. Kiln-dried stock is stable and ready for finish; unseasoned stock shrinks as it dries, so it should be allowed to acclimate before being cut and fastened. Surfaced boards are planed smooth on the faces, while rough boards are cheaper and suit framing and hidden structure.
Kiln Dried vs. Unseasoned
Kiln drying reduces moisture content and locks in the dimensions, which is why clear grades are usually specified kiln dried. Unseasoned garden grades are acceptable for fences and posts, where some checking is expected and movement does not matter. When in doubt, buy the drier board.
Storage matters on site. Keep redwood stacked off the ground, stickered so air moves between boards, and covered to shed rain. Boards stored flat on wet ground wick moisture into the end grain and stain within weeks. The process for cleaning and restoring weathered redwood siding covers sanding, brightening, and stain application, whether the boards are new or decades old.
Finishing and Protecting Redwood on Site
Redwood takes finish well because the heartwood is naturally resistant to decay, but it still needs protection from UV light, which turns it gray, and from trapped water, which can stain it. A penetrating sealer or a semi-transparent stain preserves the color; a film-forming paint changes the look completely.
Sealers, Stains, and Paints
A clear sealer needs renewal every one to three years depending on exposure; a semi-transparent stain lasts longer but hides more of the grain. Test the finish on a scrap board before committing, because redwood absorbs unevenly across heartwood and sapwood, and the two zones can end up different shades.
Site work around a redwood project involves more than the wood itself. Cutting, routing, and sanding create fine dust that irritates the nose and lungs, and power tools need the same attention as the material. Before long runs of ripping, confirm that tablesaw safety upgrades such as riving knives, blade guards, and dust collection are in place, because a kickback on a 16-foot board is not a small event.
Grade knowledge pays twice: once at the lumberyard, where it keeps the order from being overspecified, and again on the job, where the right board lasts years longer than the cheap alternative.