Glulam Perspectives: Treatment Options

Treated bridge component

Note: Glulam Perspectives is a quarterly series on Unalam’s Wood Times blog. In each article we will take an in-depth look at a project or issue facing the timber industry from our unique standpoint as a glulam manufacturer. These are our opinions and we invite constructive discussion. Next time, we will focus on a completely different topic, so stay tuned.


When you use wood outdoors, where it comes in contact with the ground, or in a wet environment, it is the best practice to use treated wood. The treatment is formulated to prevent rot, decay, and insect damage, adding durability and longevity to the wood structure. 


At Unalam, we are approved by the American Institute of Timber Construction (AITC) to glue lumber after it has been treated. We believe that this is preferable to treatment after gluing in most circumstances, because the treatment is evenly distributed throughout the glulam members and because we can manufacture large treated glulam curves that may not be able to fit into a treatment facility.


There are two types of treated wood that we glue here at Unalam: CCA, and Penta. Both have advantages in different situations. For indoor projects, such as indoor swimming pool enclosures, CCA works best. Penta is used in outdoor projects and in more extreme environments, such as bridges and marine docks. Penta is an oil-borne treatment with a strong smell, which is why it is not used indoors.

Pedestrian bridge made with treated lumber

Are there other, newer, types of lumber treatment? Yes. Why does Unalam stick with CCA and Penta for the time being? Because we manufacture a structural product, we are obligated to use these well-established and reliable treatment methods. For instance, two things we are concerned about are whether the treatment corrodes the connecting fasteners and whether the glue bond maintains integrity when using treated lumber. The risk to life safety posed by both of these situations is too great for us to consider using a new treatment before it is thoroughly tested. 


That being said, we, and others in our industry, are very interested in finding treatment methods that are safer for the end user and the planet. We are just beginning to take the first steps toward a new treatment, and it is a glulam industry-wide goal. It will take collaboration with the treatment industry to find a solution. Until we are satisfied that the new method will stand up, we will continue to use the tried-and-true methods.