What Does Retention Level Refer To?
Plain and simple, retention is the amount of preservative left in the wood after the treating process is complete. Retention is generally measured by pounds of preservative per cubic foot of lumber. There are factors that affect the retention of the wood being treated, most importantly wood species. Sapwood in the tree is more easily penetrated by wood preservatives than heartwood. Therefore, wood species known to have more sapwood, such as Southern Yellow Pine are more commonly used by wood treaters than a species like Doug Fir. Also the unique cellular structure of Southern Yellow Pine allows for a deep and uniform penetration of preservatives. All the retention information you need is on the third party inspection tag affixed to the end of the board you are purchasing. Purchasing treated lumber that is not third party inspected puts you at risk of obtaining a product that is neither code compliant nor covered by warranty. Read the tag. Just because it has a tag does not mean it has been third party inspected. Retention level of the product will dictate the use for treated lumber. We have included AWPA (American Wood Protection Association) charts for reference.
| Code | Preservative Name | UC1, 2 | UC3B | UC4A | UC4B |
| ACC | Acid Copper | 0.25 | 0.25 | 0.50 | — |
| ACQ | Alkaline Copper Quaternary (Type B or C) | 0.25 | 0.25 | 0.40 | 0.60 |
| ACQ | Alkaline Copper Quaternary (Type A or D) | 0.15 | 0.15 | 0.40 | 0.60 |
| ACZA | Ammoniacal Copper Zinc Arsenate | 0.25 | 0.25 | 0.40 | 0.60 |
| CA-B | Copper Azole, Type B | 0.10 | 0.10 | 0.21 | 0.31 |
| CA-C | Copper Azole, Type C | 0.060 | 0.060 | 0.15 | 0.31 |
| CuNW | Waterborne Copper Naphthenate | 0.070 | 0.070 | 0.11 | — |
| CX-A | Copper HDO | 0.206 | 0.206 | — | — |
| EL2 | DCOI – Imidicloprid – Stabilizer | 0.019 | 0.019 | — | — |
| PTI | Propiconazole – Tebuconazole – Imidicloprid | 0.013 | 0.018 | — | — |
| PTI | PTI plus Stabilizer | 0.013 | 0.013 | — | — |
| SBX | Inorganic Boron (Formosan termites) | 0.28 | — | — | — |
| SBX | Inorganic Boron (non-Formosan termites) | 0.17 | — | — | — |
| Use Category | Brief Description |
| UC1 | Interior Dry |
| UC2 | Interior Damp |
| UC3A | Ext. Above Ground, Coated with Rapid Water Runoff |
| UC3B | Ext. Above Ground, Uncoated or Poor Water Runoof |
| UC4A | Ground Contact, General Use |
| UC4B | Ground Contact, Heavy Duty |
| UC4C | Groudn Contact, Extreme Duty |
| UC5A | Marine Use, Northern Water (Salt or Brackish Water) |
| UC5B | Marine Use, Central Waters (Salt or Brackish Water) |
| UC5C | Marine Use, Souther Waters (Salt or Brackish Water) |
| UCFA | Interior Above Ground Fire Protection |
| UCFB | Exterior Above Ground Fire Protection |
About Post Author
