Interpreting the Mark on Pressure Preservative Treated Lumber
Pressure preservative treated lumber is a mystery to most consumers, builders and even building officials. Certainly all of the above parties understand the need for pressure preservative treated lumber when it is embedded in or in contact with the ground or concrete, or in locations where there is a high probability of untreated lumber decaying.
Where the mystery comes into play is not knowing if the pressure preservative treated we are buying is actually adequate for the intended use.
Every piece of pressure preservative treated lumber is required to be either stamped or tagged with the information shown in the box above, although the format may vary slightly. Here is the secret to understanding this quality mark:
- Is the identifying symbol, logo or name of the agency which accredits the producer – (the producer being the pressure preservative treating plant).
- Is the applicable American Wood Protection Association (AWPA) standard and Use Category. THIS IS THE IMPORTANT ONE. For lumber to be embedded in the ground and used structurally it must be treated to a UC-4B standard. For more on this subject, what I believe may be one of my best articles ever is here: https://www.hansenpolebuildings.com/2014/05/building-code-3/.
- The year of treatment if required by AWPA Standard/Use Category.
- The preservation used, which may be abbreviated.
- The preservative retention. In the “olden days”, the standard for treating was “.60” which everyone knew was CCA treated for structural in ground use. More reading on the post-CCA world here: https://www.hansenpolebuildings.com/2016/01/pressure-treatment-beyond-cca/
- The exposure category (e.g. Above Ground, Ground Contact, etc.). This really confuses too many people as both UC-4A and UC-4B say Ground Contact.
- The company name and location of home office; or company name and number; or company number.
- If applicable, moisture content after treatment. This is crucial to the glue laminated column manufacturers as the glue laminating process relies upon very low moisture content lumber.
- If applicable, length, and/or class.
Just because lumber is pressure preservative treated, does not make it all the same. Learn to watch for the level of treatment on every piece of lumber. You will be glad you did.