I was in communication with John Wagner a couple months ago about an article he wrote that was published in Residential Design/Build Magazine on Foam Insulation. I will get to that next week, but first lets talk about wood preservatives, something that comes up every time we design the deck. At Gravitas we have always discuss what is the most responsible way to specify the treatment of wood in decks and porches. Code says “rot resistant” and we take that to mean that you could use sustainably harvested rot resistant species of wood such as redwood or cedar. Unfortunately these species have a decreased structural capacity and thus you need more tightly spaced joists, and/or more girders to shorten the spans of the joists. This always pushes us in the search for the greenest wood treatment options. In the article below John Wagner has outlined some good options, at least the best of the worst so to speak. John, thanks for sharing your knowledge again.
By John Wagner
We are seeing some real innovation with wood treatments these days; whether it’s wood for decking, siding, or part of the structural frame. At the root of this topic is the fact that, when left untreated or when unprotected, wood can rot. Even premium species like cedar and redwood—which are naturally decay- and rot-resistant—require treatment to extend their useful lives.
Today’s wood treatments range widely from chemical treatments to heat treatments (a.k.a. “thermally modified wood”). And if you are looking for the green angle here, 
the simple fact that wood treatments can dramatically extend the life of the wood is a very “green” attribute indeed—in a life cycle analysis, it lowers the environmental costs of re-harvesting (and re-treating, and re-shipping and re-installing) replacement wood products. However, each wood treatment method has its merits, and each one has features that can make it more or less green. Let’s take a closer look by first reviewing a brief history of wood treatment.
Chromated Copper Arsenate (CCA)
For a long time, Chromated Copper Arsenate, or “CCA” was the formula for treating lumber. For decades, it was common to see “green” CCA decks – the green was the color of the oxidized copper. And CCA-treated wood was also commonly used in most ground-contact situations. In the ‘90’s new alternatives to CCA were introduced. None took meaningful market share from CCA because none could match its performance and value. As the millennium approached, there was increased scrutiny regarding the perceived safety of CCA as reported by various “consumer advocate” reporters and environmental organizations. In 2003, treaters voluntarily stopped using CCA for residential applications and newer, more expensive formulations replaced CCA. One bright spot that emerged from the demise of CCA was that the pace of innovation in preservative development quickened.
Alkaline Copper (ACQ) & Copper Azole (CA-B)
The replacement wood preservative treatments were ACQ and CA-B. Let’s first look at ACQ. ACQ is a treatment consisting of alkaline copper, a fungicide, and quaternary ammonia (sometimes called quat), which serves as an insecticide. On the other hand, CA-B is a treatment containing mostly copper and azole; the azole is a fungicide that appears in various chemical forms. If you step back and take notice, there are two consistent elements in these approaches to wood treatment. One, they all are aimed at stopping rot, decay, fungus, and insects from getting to the wood. And two, they all overwhelmingly contain copper, a natural, harmless wood preservative. As wood treatments have evolved, some wood treaters (and the chemical companies that license their formulas to these wood treaters) have stayed with copper. But they have eliminated other chemicals in their wood preservative formulations.
Micronized Copper (MCQ)
Among the most positive result was the recent introduction of a new micronized copper wood preservative. Developed by Osmose, Inc., and marketed as ProWood Micro (MCQ Treated Wood), the new process bonds microscopic copper particles to the wood cells. Because of this there is no need for a solvent (which is still used in most other non-micronized formulations) . These 
attributes have earned the ProWood Micro formulation Environmentally Preferrable Product (EPP) status from Scientific Certification Systems, a leading third party certification firm. This is the first and only such preservative to earn this recognition. To earn EPP certification, a product must demonstrate reduced impact on human health and the environment when compared to other products that serve the same purpose as measured by guidelines published by the U.S. Environmental Protection Agency.
Non-metallic
There is another relatively new product out today that is offered by Arch Wood Protection. The treatment is Wolmanized L³ Outdoor wood. It contains no copper as part of the preservative and uses a proprietary non-metallic preservative.
Boric Acid
Yet another class of wood treatment is focused on boric acid, as well as its oxides and salts which are called borates. Boric acid is a very-effective wood preservative. Conveniently, it is toxic to insects, but it has low toxicity with humans. That said, the problem with boric acid has always been that it is water-soluble. That means it can be floated into wood with water-based pressure treatments or applied with surface applications. But the boric acid will eventually leach out of the wood. That leaching process is dramatically accelerated if the wood is exposed to the elements. All of this means that wood treated with borates isn’t generally good for ground contact, and in any application, it has to be re-treated repeatedly with borate applications to ensure that the wood is preserved. Now, because borates have gotten another look from consumers, due to the perceived toxicity of alternative wood treatments, borates have seen some innovative uses. One company floats borate deep into wood fiber by mixing it with glycol, a kind of alcohol. The glycol flashes off, leaving the borate behind, and until the borate leaches out, it is a good termiticide, insecticide, and wood preservative. But here too, the wood has to be re-treated regularly.
Thermally-Modified Wood (TMW)
Another kind of wood treatment that you see gaining wider acceptance is heat treatment. Wood that is treated with heat is generally referred to as thermally-modified wood or TMW. This treatment process contains no chemicals or additives at all. Like its name says, the thermally-modified process uses high heat and steam to change the very nature of the wood. In fact, the thermal process removes the aspects of the wood that serve as food. With no insects, fungus, or mold attacking the wood, the thermally-modified process can prevent for rot and decay. Specifically, the process removes or de-natures the sugars in the wood, leaving behind aspects of the wood that cannot be digested by insects or eaten by fungus and mold. After the wood is thermally treated, it can be stained, sealed, joined, and glued like regular wood.
No matter what type of treated wood you seek, you should be aware of its code acceptance. Some treatments are not code compliant, even though they have been around for a number of years. To get code approval, preservative companies can either work with the American Wood Protection Association (AWPA) to have their treated wood listed in the AWPA Standards. Or the preservative company will work with the International Code Council (ICC) Evaluation Service to earn an Evaluation Service Report (ESR). Without the support of either an AWPA listing or an ESR, there is no guarantee that a local code will allow a product on the job where treated wood is required. So, check the fact sheet from the wood provider or the wood treater to see if the wood is approved for use.
