What pressure-treated lumber means
Pressure-treated lumber is wood forced full of preservative under pressure so it resists rot and insects, for use outdoors and in contact with concrete or soil.
Also called PT lumber, treated lumber.
Where it matters on a carpentry job
Treated wood has ratings for above ground and ground contact; using the wrong one for posts is a common failure. It also needs fasteners and connectors rated for the chemicals.
What the model code says
- Deck ledgers are at least 2 by 8 nominal, pressure-preservative-treated Southern pine, incised treated hem-fir, or approved naturally durable lumber of No. 2 grade or better. (IRC 2021, Chapter 5)
Check which code edition your building department enforces for pressure-treated lumber before you quote.
Work it out
- Free calculator: Deck cost calculator
- Tools, templates and guides: Free carpentry resources
Sources: 2021 International Residential Code, Chapter 5, Floors (ICC). Checked October 9, 2026.