Not All Pressure-Treated Lumber Is the Same — Read the Use-Category Tag

The Problem

"Pressure treated" reads like one product, and it's several. The green boards at the lumberyard span a wide range of preservative retention levels, and the difference between them is the difference between a beam that shrugs off ground contact for decades and one that rots in the same spot in ten years. Most buyers never look past the color.

The Technique

Read the end tag: every stick of treated lumber carries an AWPA Use Category rating that says what exposure it's actually treated for.

• UC3B — exterior, above ground, exposed to the weather: typical deck boards and railings.
• UC4A — general ground contact: posts and framing that touch soil.
• UC4B — "Critical Structural Components": heavy-duty ground contact, treated to a retention level just shy of what docks and utility poles get.

The builder here chose UC4B for structural members he wants to last — and paired it with another longevity move, elevating the wood on standoff blocks so it isn't sitting directly in the wet.

Ask for the category you need; if the yard's rack only holds UC3B, ground-contact stock can be ordered.