Stacked wood
12 April 2013

What Does Retention Level Refer To?

Stacked wood

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

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