You can use treated wood for a variety of projects including, but not limited to, decks, retaining walls, fences, fire-resistant applications and marine pilings. Treated wood is vital in many of these different applications because there are naturally-occurring fungi in the ground that attack lumber, so lumber destined to be used in the ground must be treated to a higher standard, or retention level, of fungi-resistant preservatives in the wood. The end tags on treated lumber will provide you with proper use designations. Look for Above Ground or Ground Contact on the end tag.
AWPA Use Categories for Typical Construction Applications
UC3B (above ground, exposed) – wood and wood-based materials used in exterior construction and not in contact with the ground.
- Materials do not require an exterior coating but may be finished to achieve a desired aesthetic appearance.
- Materials are used for a variety of applications in either horizontal or vertical positions such as decking, sills, walkways, railings, fence pickets, uncoated millwork and joists/beams for decks and freshwater docks.
UC4A (ground contact, general use) – wood and wood-based materials used:
- In contact with the ground, fresh water, or other situations favorable to deterioration
- Above ground but are difficult to maintain, repair or replace and are critical to the performance and safety of the entire system/construction
- Above ground but may end up in ground contact or are subject to hazards comparable to ground contact due to climate, artificial or natural processes or construction
Examples are fence posts, deck posts, guardrail posts, structural lumber, joists and beams for decks and freshwater docks.
HEAVY-DUTY GROUND CONTACT
UC4B (ground contact heavy-duty) – wood and wood-based materials used:
- In contact with the ground in severe environments (such as horticultural sites)
- In climates with high potential for deterioration
- In critically important components such as utility poles, building poles and permanent wood foundations
- In salt-water splash zones
UC5A-C (marine use) – wood and wood-based materials exposed to salt and brackish water
UCFA (fire retardant interior) – used in interior construction where wood is not in contact with the ground and is protected from exterior weather
UCFB (fire retardant exterior) – used in exterior construction that is not in contact with the ground but may be exposed to the full effects of weather
For great tables to use for use categories go to the following link: