0.020″ initial sag
0.008″ per foot · ~0.030″ after years of load (creep)
Stiff enough — sag should be invisible in normal use.
Guideline: keep sag at or under 0.02″ per foot of span (≈1.7 mm per meter). Stiffness values are typical for kiln-dried stock at ~12% moisture content; individual boards vary.
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