Pressure-Treated Wood Stack Height Calculator

In 2026, a PT yard manager in Savannah accepts 14 truckloads of wet ACQ 2×6×12 from a Georgia treatment plant. Each unit measures 124 inches tall fresh from the cylinder — but the yard's storage racks were sized for the post-cure 119-inch height. The four-inch difference matters: stacks above the rack rails fall when banded. This calculator was built so material managers never get caught by the wet-versus-cured gap again.

The shrinkage problem traces to a 1924 industry decision codified in PS 20-20: lumber is graded and sold by the finished cured dimension. Pressure treatment, introduced commercially in the 1830s by John Bethell's creosote process, adds water to wood after surfacing. To meet the post-cure spec, mills must oversize the rough-sawn dimension by 3-5% — typically dressing wet PT 2× framing to 1.55″ × 5.65″ instead of the standard 1.5″ × 5.5″.

The American Wood-Preservers' Association — founded in 1904 and now the source of every U.S. pressure-treatment spec — sets the cure-state expectations in AWPA U1 and T1. Fresh treatment cylinder discharge carries 90-150% moisture content. After 48 hours of drip-drying, lumber loses about 30% of carrier water but core MC remains above 70%. Bulk drying to ambient takes 4-6 months in the southeastern U.S. climate where most pressure treatment occurs.

Shrinkage is anisotropic. Radial shrinkage (across growth rings) averages 4% for Southern Yellow Pine; tangential shrinkage (along the rings) averages 7%; longitudinal shrinkage is negligible (0.1%). Because most dimensional lumber is plain-sawn, the wide face shrinks more than the narrow face — a 2×6's 5.65" width loses more than its 1.55" thickness in absolute inches.

KDAT (kiln-dried after treatment) was developed in the late 1990s as a premium product for paint-and-stain finishers. After the standard pressure cycle, KDAT lumber re-enters a heated kiln and dries to ≤19% MC at the mill. KDAT 2×6 ships at the same 1.5″ × 5.5″ dimension as kiln-dried untreated lumber — and stacks measure identical heights. The premium runs 15-20% over standard wet PT but eliminates surprises in rack sizing and trailer planning.

Untreated kiln-dried lumber stacks identically across products, which is the subject of our untreated lumber stack height calculator. The PT-specific math here applies only when the cure state matters — typically the first six months after the cylinder. After cure, PT and untreated lumber stack to within 0.05 inches per layer.

Building inspectors and code officials cite IRC R317 for treated-wood applications and reference AWPA UC categories (UC3A through UC4C) for required retention. Stack-height violations rarely show up in inspections, but trailer-load DOT violations are common — most $1,000+ axle weight tickets trace back to a yard manager who planned the load to the cured dimension instead of the wet shipping dimension.