Treated Wood: Construction Tips from the Experts

Rob Pongonis, YellaWood brand manager, offers his expert advice on best practices when working with treated lumber.

Backyard building is big business. For years, this trend in home-improvement has been on the rise, and now that people are spending more time at home than ever, the trend is exploding. Decks, docks, pergolas, patios, outdoor kitchens and exterior furniture--these are the things than transform a backyard into an enjoyable living space.

One of the most fundamental building materials for outdoor construction remains pressure-treated wood, which has undergone a process that uses high pressure to force a solution of water and preservatives deep into the lumber to extend its lifespan. The active ingredients commonly used in treated wood are alkaline copper quaternary (ACQ), copper azole (CA) or micronized copper azole (MCA), which react with the wood fibers to slow decay and resist termites, fungus, moisture and other harmful elements. This process enables treated fence posts, for example, to withstand years of being buried in soil.

Treated wood is a renewable and affordable and usually readily available, although the high demand of recent months might leave your supplier waiting on the next shipment from the mill. According to a July 9, 2020 article from the Wall Street Journal, "Prices for forest products like lumber and plywood have soared because of booming demand from home builders making up for lost time, a DIY explosion sparked by stay-at-home orders, and a race among restaurants and bars to install outdoor seating areas.”

Demand continues to rise because even when prices are up, treated wood remains one of the most economical outdoor building materials available. One of the leading manufacturers of treated lumber, Great Southern Wood Preserving--the makers of YellaWood brand treated products--is now celebrating its 50th anniversary in business. To get some expert advice on best practices when working with treated lumber, HIR turned to YellaWood brand manager Rob Pongonis to clear up a few questions.

Whether you're a pro builder or a homeowner, here's some "insider" insight on what to consider when planning your next project.

What should builders and homeowners understand about selecting different grades of treated lumber for a project?

Pongonis: As a contractor, when you’re meeting with a homeowner to discuss a deck project, it’s important to listen and to ask as many questions as possible to ensure you understand exactly what they’re looking for from their investment. Most homeowners have a vision for their project that includes functionality and color but they often don’t fully consider the appearance of the deck boards. That’s why talking about grades, especially knots and other beauty factors, early in the process is so important. And many homeowners may not realize they have options when it comes to the appearance of deck boards. While many building supply stores stock a couple of grades, there are more options available through special orders that may better meet the homeowner’s expectations. Using a “Good, Better, Best” approach clarifies the options in an easy to follow way.

When talking about deck boards, it is important to remember 5/4 decking is a popular choice and commonly available in two grades: Standard and Premium. 5/4 Standard decking would fit into your “Good” category and will have some large, sound knots and some bark edges. 5/4 Premium decking is a step up and would fall in your “Better” category. These products will have less bark and smaller, more well-spaced knots that appear less frequently than what appears on Standard grade.

What is the latest advice on building applications that require ground-contact lumber?

In 2016, the American Wood Protection Association (AWPA) wanted to address growing concerns around the incorrect usage of treated wood. They released a revised standard which governed the use of Ground Contact treated lumber. This revision required Ground Contact products to be used in some applications where Above Ground products had previously been approved.

Today, the AWPA recommends using Ground Contact treated products in any applications that are difficult to maintain, repair or replace and critical to the performance and safety of the structure. This includes applications such as joists, beams and ledger boards. In addition, they require Ground Contact treated deck boards when placed closer than 6 inches to the ground, have poor air circulation or poor water drainage, or are exposed to frequent wetting like freshwater docks, sprinkler systems, or swimming pools and other such hazards.

The good news is most building supply retailers helped take the guesswork out of this by stocking only Ground Contact treated lumber. However, it’s always a good idea to check the end tag to make sure it clearly states “End Use: Ground Contact” before beginning construction.

Is it necessary to use peel-and-stick flashing when treated wood is used in contact with aluminum products?

YellaWood brand products are treated with a micronized copper preservative which exhibits corrosion rates on metal products similar to other non-corrosive treatments and untreated wood. Aluminum building products may be placed in direct contact with YellaWood brand products without the need of additional flashing as long as there is proper water drainage and the wood isn’t exposed to, or remain in contact with, a continual moisture source, standing water or water immersion.

Editor's note: Not all wood is treated the same, and some different copper-based preservatives used by other brands have been reported to cause corrosion when placed in direct contact with aluminum products, such as ledger-board flashing. This has prompted builders to isolate the aluminum from direct contact with the framing lumber by using a peel-and-stick membrane. Check with the lumber manufacturer for the latest guidelines on your specific product.

What type of fasteners (type and materials) do you recommend for outdoor construction?

When selecting fasteners and hardware, it is important to make sure you are in compliance with the manufacturer’s recommendations and building codes. In exterior applications, fasteners should be either be Hot-Dip Galvanized (ASTM-A153), Epoxy Coated Carbon Steel (Zinc Plated, AC-257) or Stainless Steel (304, 305 or 316). YellaWood Outdoor Fasteners are star-drive fasteners available in a tan epoxy-coated carbon steel or stainless steel options. They are available in deck screws and trim screws in a variety of lengths.

Explain the best procedure for preserving the treated lumber when it has been cut on the job site.

Sealing field cuts is a great idea to provide extra protection to your project. Preservative products can typically be found on the paint aisle at most home centers. Suggestions can include a copper naphthenate (2% as metal).

How deeply does the preservative treatment penetrate into a lumber product? Are thicker boards such as 4x4 or 6x6 any more susceptible than 2x lumber to rot or water damage by virtue of having more mass (and presumably less chemical absorption at their core)?

There are certainly factors that play into how well the wood takes the treatment like the presence of heartwood and the moisture content, but the treatment process is designed to drive the preservative deep into the cellular structure regardless of thickness. Following treatment each charge goes through a rigorous quality control test. Core samples are drilled and tested to see both how deep the preservative went and how much of the preservative was retained in the wood. What’s more, we also have a contract with a third-party testing service that regularly inspects our products for quality (a service not all treaters subscribe to). And of course, we offer and proudly stand behind our warranty.

What advice do you have for applying stain/sealers to an outdoor wood project?

“When do I stain my deck?” is probably the top question we get from homeowners. The answer is simple: As soon as possible. In application, however, it’s a lot harder to predict. The wood has to be dry enough to accept the stain which can be impacted by factors like local weather patterns. The best way to tell if your boards are ready to be stained is to splash a few drops of water on them. If it beads up, wait several days to test again. If the water absorbs into the wood, you’re good to go. When it comes to application, we recommend following the manufacturer’s instructions and testing the stain on a small area to make sure you’re happy with the color before expanding to the full area.

Anything else you’d like to add?

Great Southern Wood Preserving, Inc. recently celebrated its 50th anniversary and announced a partnership with NASCAR in which the YellaWood brand sponsors the fall NASCAR Cup Series playoff race held at historic Talladega Superspeedway. Tickets for the 2022 YellaWood 500 are available via an early access pre-sale.

All photos appear courtesy Great Southern Wood Preserving, Inc.