Douglas Fir-Larch is the structural benchmark among North American framing species. Highest bending values of the common framing species, the stiffness long spans need, and a timber tradition that goes back as far as wood-frame construction on this continent. It is also routinely specified where it is not needed and skipped where it is. This page covers what Douglas Fir actually is, how it is graded, and where it earns its price.
"Douglas Fir" on a grade stamp is usually Douglas Fir-Larch, a species combination of Douglas Fir and Western Larch graded and marketed together. It grows big, straight, and dense in the Pacific Northwest, which is why it dominates the timber and long-span end of the market. Its design values lead the common framing species in bending and stiffness, which is exactly what governs the spans where framing gets difficult.
Select Structural. The top structural grade. Specified where design values must be maximized or appearance and strength both matter.
#1 & Better. The workhorse of exposed timber work: near-Select values with the appearance to be left visible. Free of heart center stock in this grade is the standard call for large timbers that will dry in place.
#2. The default framing grade. Most span tables you have ever used assume it.
Decking grades. T&G decking carries its own grade rules and design values, separate from dimension lumber. A "Select Dex" stamp is not the same claim as "Select Structural."
Dimension lumber and timbers are graded under different rules with different design values. A 6x12 is not a big 2x12, and its numbers come from the timber tables, not the dimension tables.
Dimension lumber is normally kiln dried. Large timbers are normally surfaced green and dry in service, because you cannot practically kiln dry a 12x12. That means checking is normal, shrinkage is real and predictable, and connection details for big timbers must be designed for movement. Specifying free of heart center stock is the single most effective step for controlling checking in exposed timbers.
Where it does not: short spans, hidden framing, and anything a span table clears in SPF. Paying Douglas Fir money for closet walls is a specification error in the other direction.
In design values, yes, across bending and stiffness for equivalent grades. Whether that matters depends on whether your span is close to the limit. At half the allowable span, the cheaper species is the right call.
Free of heart center. The timber is sawn to exclude the pith, which dramatically reduces splitting and checking as the timber dries. It is the standard specification for exposed Douglas Fir timbers and worth the premium there.
Dimension sizes, yes, routinely. Large timbers, generally no. Big DF timbers ship surfaced green and season in place, and good detailing accounts for that.
Untreated, no; it is not durable in ground or weather contact. Treated Douglas Fir exists but treats less readily than Southern Pine, and incised treated DF takes a strength reduction. For most decks the treated framing species of your region is the better call, with DF reserved for the covered, exposed structure above it.
Design values and grade descriptions on this page are general reference for comparison and planning. They are not engineering, not sealed drawings, and not a substitute for design by a licensed professional under your local code. Final member sizing, connections, and load paths must be confirmed for your specific project.
Bardowl Design produces structural layouts and material specifications that builders and lumberyards can actually work from. Clear scope, defined assumptions, documented output.
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