When To Use Treated Lumber in the Tropics

What is Pressure Treated Lumber?

Let’s start with understanding what pressure treated lumber is to understand why treated lumber should be used in many projects in the tropics. The process of treating the wood involves using high pressure to inject the wood with chemicals or preservative agents, which protects the wood from insects, rot and decay from moisture. It essentially extends the longevity of the wood, extending its lifetime by decades.

In most cases, treated lumber should be used in outdoor projects where moisture is present. However, although moisture is one of the main risk factors in bio-detioration, dry wood can also be vulnerable to attack by termites and other insects. Using treated lumber in the tropics should further protect you from this. 

Examples of treated lumbers most common use cases are in decks, fences, railings, picnic tables, roof slats and corner posts. There are 2 main types of pressure treated lumber to be aware of: above-ground and ground contact. Your use case will dictate which type of treated lumber you should pick for your next outdoor project.

Above Ground Treated Lumber

As the name suggests, above-ground treated lumber are for outdoor applications that are above the ground. It is recommended to leave a space of at least 6 inches above the ground, as recommended in the International Building Code. Examples when to use above-ground treated lumber include deck railings, porch flooring, joists and beams. It can also be considered for sub-flooring in kitchens and bathrooms, as water leaks are common in these areas.

Ground Contact Treated Lumber

Ground-contact lumber should be used when the wood will be in contact with the ground, or the installation of the wood is less than 6 inches off the ground. You should also consider using ground-contact treated lumber if you are building the tropics, or if it will be installed in an area where the wood will get wet frequently without enough time to dry or in areas where there is low air circulation. Ground-contact lumber has a higher chemical concentration than above-ground treated lumber. 

In summary, the ground contact lumber has been treated to a higher standard to withstand rot and decay when in contact with the ground or when exposed to excessive moisture and high humidity environments. Above-ground lumber has been treated with a lower chemical concentration, and so it is less resistant.

Safety Considerations for your Treated Lumber

Some safety considerations should be taken into account when dealing with pressure treated wood. Given the high concentration or preservatives used in treated lumber, non-treated wood is preferred for indoor applications and in structures where children and pets frequent regularly. Examples of these include play sets and dog houses. If these structures are built outdoors, natural rot-resistant woods such as cedar, are a better compromise for health and safety reasons.

Pressure treated wood doesn’t release harmful particles or gases, so if you are not cutting the wood or are exposed to its sawdust, you will be fine. However, in some cases it is recommendable to apply oil-based sealants to your treated wood. Oil-based sealants limit the amount of copper, arsenic and other compounds from reaching the surface of the lumber. However, there is no need to use these sealants on treated wood when it will be hidden from direct access, such as sub-flooring.

AWPA Use Categories 

The American Wood Protection Association (AWPA) publishes a Book of Standards annually. In this guide, the AWPA outlines the suggested preservatives and retentions for various service and intended uses.