Have You Heard of Accoya?

What is Accoya? No, it’s not a bookshelf at IKEA. It’s the next generation of treated lumber that I have been experimenting with for a few years now. The results have been surprising and I’m ready to give you my thoughts.

We all want to avoid rot, right? Does anyone here appreciate termites and powder post beetles? I thought I might know the answers to those questions, but the bigger question is this:

“Is there an attractive alternative to the ugly green PT lumber we’ve all be relegated to using the last half century?”

Sure, you can use old growth lumber when you can find it and deal with the nail holes. I love the character of old wood, but I don’t want to waste it on paint grade outdoor projects that don’t call for heritage quality woods.

You’ve also got the option to use exotics like Mahogany, Spanish Cedar, and Sapelle to name a few, but those aren’t consistently available in my experience and are rarely sustainably grown (I don’t like cutting down rain forests FYI).

That leaves us with standard PT lumber, right? That works well for decks and rough stuff but when I am building doors, windows, exterior trim, or anything else that needs a more refined look, I’m left with very few wood options. Last week I talked about cement board options like Hardie Trim, but sometimes you need wood and I want to have a wood option that won’t rot away in a few years!

What is Accoya?

Accoya is the next generation of treated lumber that is non-toxic, sustainably grown, dimensionally stable, and extremely resistant to rot and insect damage. Check out the video below for a quick explanation of Accoya.

Accoya is FSC certified sustainably grown Radiata Pine that undergoes a special treatment process called acetylation. For the science nerds, here’s what happens: The chemical structure of wood typically contains hydroxyl groups, which encourage the uptake of water (trees need water to grow right?). During the acetylation process, those hydroxyl groups are changed to acetyl groups. This new cell structure of the wood results in a wood that absorbs 80% less water, is no longer recognized by mold and fungus as food, and is indigestible by insects. Those are three major scores!!

The acetylation process uses an industrial vinegar. Think of it like pickling a cucumber. That same cucumber can sit on the shelf for months or even years without rotting due to the chemical change it has undergone. That’s why your shop will smell like a deli when milling Accoya!

Advantages of Accoya

• 50 yr above ground/25 yr in-ground warranty against rot
• Dimensionally stable (no more swelling, twisting, bowing or warping)
• Extremely hard wood, similar to mahogany Janka rating
• Longer paint life (due to decreased wood movement)
• Accepts stains and varnish well
• Non-toxic, natural wood product
• FSC certified renewable resource

Disadvantages of Accoya

• Requires stainless fasteners
• Prone to increased blowout during milling processes
• Limited availability
• Not locally sourceable

To me, the advantages far outweigh the disadvantages, but I happen to be one of the few folks who live near a distributor of Accoya. That local availability is likely the reason you have either heard of it or not.

My Thoughts on Accoya

For about four years I have been using Accoya to build a variety of projects in my shop. We’ve made window sash and jambs, doors, porch flooring, custom moldings and even corbels (check out that video here!)

I have painted it, stained it, drilled it, run it through a jointer, planer, table saw, mitre saw, shaper, and anything else you can do to wood and it has become a favorite of mine in most regards.

Two issues when working Accoya are that it does create a little more blowout unless you use a spoil board because it is more brittle than some other woods like pine and cypress. Also, it does not turn on a lathe at all, too hard and brittle.

The big wins for me are the rot and insect resistance and the dimensional stability, which means that my windows and doors will fit perfectly year-round instead of shrinking up and being gappy in the winter and swelling themselves shut in the summer.

All of us woodworkers have our favorite woods to work with and it’s hard to convince most of us to try something new and relatively untested, but in my experience, Accoya is worth taking a look at and seeing if it might be worth a try in your shop.

At the time of this writing Universal Forestry Products (UFP) seems to be one of the only distributors of Accoya in North America for now. I’m hoping that will change and it will become easier to get your hands on.

Have you tried Accoya? Let me know your thoughts in the comments below.