Treatment Specification Guidelines

In July 2016 the U1 standard was revised by AWPA to require sawn lumber and timber used in above ground exposed conditions be preservative treated at the UC4A level, just like general ground contact use conditions, if the preservative treated wood used in Joists and Beams are difficult to maintain, repair, or replace, and are critical to the performance and safety of the entire system/construction. It is the responsibility of the designer and or builder to determine the proper treating specification given the end use and use environment.

AWPA UC4A Guidelines for Treated Wood Apply When:

1. Treated wood is installed less than 6” above the ground. 2. Ground contact treated decking should always be used on ground level decks and walkways. 3. When treated wood is used in an application that does not permit air circulation or water drainage underneath the structure. 4. When treated wood is used in an application where vegetation, leaf litter, or other debris will build up and remain in contact with the treated wood product. 5. When treated wood is used in an above ground application where the treated wood component would be considered difficult to maintain, repair or replace and that component is critical to the performance and safety of the structure. 6. When treated wood is wetted on a frequent or recurring basis such as wind and wave action (such as fresh water docks and walkways) or watering systems, swimming pools and hot tubs. 7. When treated wood is used in tropical climates. Deterioration Zones from AWPA Standards There are major regional differences in the potential for deterioration of wood as shown in the Deterioration Zone map. In some cases multiple retentions are shown in the AWPA Standard, so users may address variances in potential deterioration in their area. The higher retention levels should be considered by the designer when wood is installed in the higher deterioration zones, as shown in the following map.

Severe High Intermediate Moderate

Low

Waterborne Treatment It has long been the glulam industry’s position that waterborne preservative treatments are not recommended for glulam products. Glulams are manufactured from kiln-dried lumber and waterborne treatments cause the beams and columns to take on a high moisture content during the treating process resulting in dimensional changes such as swelling, warping, twisting, excessive checking, splitting and raised grain, resulting in an unacceptable finished appearance.

Field Treatment Preservative treatments create an envelope of protection around each piece of treated wood. Severe checking or splitting that extends beyond the treated envelop can allow moisture or insects to gain access to the untreated wood in the center of the piece. Where possible, fabrication or machining should be performed prior to pressure treatment. All field cuts, holes or beam damage that occurs after treatment must be field treated to protect the exposed wood material. Application of a copper naphthenate solution having a minimum 2% metallic solution is specified in accordance with AWPA Standard M4. Field treatment is not as effective as pressure treatment so the designer should consider

Any treated product quoted or sold is done so on the assumption that purchaser has made the determination of suitability of the product. Rosboro makes no warranty or representation, either expressed or implied as to the performance of treated products. Since the conditions of use and application are beyond our control, Rosboro disclaims all liability and assumes no legal responsibility for damages resulting from use.