The New Pressure-Treated Wood

The EPA has  banned  CCA lumber. The replacements are safer, but they may change how you use pressure trested lumber.

    Nearly 40 million lb. of arsenic is used in this country every year, and most of it goes into the pressure-treated wood that we use to build decks and playgrounds. But that all changes Jan. 1, 2004. The Environmental Protection Agency (EPA) is banning chromated copper arsenate (CCA) as a preservative for wood intended for residential use (except for the lumber that is used in permanent wood foundations). CCA-treated lumber will still be available for industrial and agricultural use, however.

By the way, there's no need to panic about existing CCA-treated structures. The EPA says that they're fine. But if you're nervous about the chances of leaching chromium and arsenic, you can make your deck or swing set safer by coating it with an oil-based penetrating stain every couple of years.

Taking CCA's place as a preservative are two waterborne compounds: alkaline copper quat (ACQ types B and D) and copper azole (CBA-A, CA-B). Sold under the trade names Preserve, NatureWood, and Natural Select, they have been used around the world for up to 15 years. These EPA-approved low-toxicity pesticides resist bugs, mold, and rot as effectively as CCA.

                         ALUMINUM FLASHING:

Perhaps the most important point to keep in mind relating to copper-based wood treatments and galvanic corrosion is to avoid aluminum flashings altogether. Aluminum corrodes quickly in the presence of high copper concentrations.

        When metals from near the top of the Electromotive Series, such as aluminum, come in contact with metals on the lower end of the series, such as cooper, there will be rapid corrosion when surrounded by an electrolyte, such as water.

That's why you don't want to put aluminum flashing in contact with wood treated with copper. When the materials get wet, holes will be eaten in the aluminum flashing due to corrosion.

Why is it a problem?

Code requires flashing on decks so water will not migrate under the siding and cause rot/decay in the untreated house framing. If the material used for flashing develops holes, the water will pass through it. This is what will happen once the copper eats holes in the aluminum flashing.

Finally, double-check the joist hangers

Joist hangers, if they were used on your deck, are another potential trouble spot. They are susceptible to the same corrosion problems as fasteners.

They should be made from stainless steel or galvanized steel with a G185 coating thickness.

Connectors made with thinner galvanized coatings can be used in some conditions as long as they are protected from direct contact with treated wood.

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PRESSURE TREATED WOOD FOR RESIDENTIAL USE

     Beginning Jan. 1, 2004, CCA pressure treated wood was no longer produced for residential use. The CCA treatment used a chromium-copper-arsenic compound to prevent wood decay and infestation by wood destroying insects, but because of public concern with this chemical treatment, the wood preservative industry decided to replace it with other preservative chemicals which are equally effective.

     Two alternative treatment processes have undergone review and testing, and are accepted by the current building codes. These are: Wolmanized Natural Select Pressure Treated Wood, and Nature Wood Preserved Wood Products. In addition, other treatment chemicals/methods are undergoing tests, and may be available in the future. Additional information about products can be obtained by obtaining a brochure from the lumber retailer, or by visiting the web site of each company.

     The Wolmanized Natural Select Pressure Treated Wood web site is www.naturalselect.com.

     The Nature Wood Preserved Wood Products web site is www.osmose.com.

     These new chemical treatments have eliminated the chromium and arsenic previously used in CCA treated wood. The new treatment processes rely on a new formula copper compound, along with small amounts of other insect and fungi control agents. While these formulas do an excellent job of protecting the wood, precautions must be taken when using the treated wood. The following highlight must be observed:

        Hot-dipped galvanized fasteners and hot-dipped galvanized connector brackets must be used. The new treatments are more corrosive to steel than the CCA treatment, and electroplated steel is not adequate.

        Alternatives to hot-dipped galvanized fasteners are listed and attached. For example, stainless steel, ceramic coated steel screws, and other fasteners listed in the attachment may be used. Most nail gun manufacturer’s have hot dipped galvanized fasteners available for their line of tools.

        Aluminum flashing may not be used in contact with these new wood products. The high copper content of the chemical will quickly corrode aluminum.

     The CCA treated wood was readily available with a 0.40 PCF retention rate, which was suitable for ground contact and above ground use. Although 0.25 PCF treated CCA lumber was suitable for above ground use only, most lumber suppliers did not stock the two different grades. The 0.40 PCF treated wood cost a small amount more than the 0.25 PCF treated wood, but the extra space and cost of stocking two different lumber grades more than offset the small additional cost of the additional treatment. Thus the lumber retailers stocked only the 0.40 CCF treated wood.

     The new treated wood products are available in two grades: above ground use and ground contact use. Look at the small tag on the end of each piece of lumber to be sure you are using the properly treated wood in the location for which it is designed. If the lumber retailers find that the cost of stocking two different grades of lumber is costly, they may decide to eliminate the above ground use product, and sell only the ground contact product.

     The most commonly treated wood is Southern Yellow Pine, and the strength of this wood with the new treatments, remains equal to the CCA treated wood.

     The “A” in CCA stood for inorganic arsenic which worked well in keeping insects and microbes from destroying the wood, but introduced a potent poison into the environment. Today’s pressure treating chemicals rely on copper alone in new formulations. You will see codes such as ACCQ-C, ACQ-D, and ACQ-D Carbonate on some lumbers. These are all versions of Alkaline Copper Quatenary. Other pieces of lumber will bear codes like CBA-A or CA-B which indicate they were treated with a Copper Azole-based material. The commonality among these materials is in the use of copper as the primary decay-preventing chemical. Research so far indicates that these new materials should work to prevent decay for decades much as the old CCA treatment did.

     One of the big changes you will notice when you purchase these new pressure treated woods is in the price. The new lumber is going to cost you more since the new treatments cost more. Our long-term expense as a society will probably be lower if you factor in that we will on longer be creating massively expensive to clean up toxic waste sites as we did with CCA treatment plants.

     Another change is in the grades. Pay careful attention to the specific application on the end tag. Due to the higher expense of the new chemicals and the fact that we don’t always use the wood in contact with the ground, some of the wood will bear the recommendation “Above Ground.” Less chemical has been forced into the wood to save money. Be sure to use only wood labeled for ground contact as posts or retaining walls. The key for the consumer is to read the end tag on the lumber. Any lumber sanctioned by the American Wood-Preservers Association will bear their initials “AWPA” and have a fairly easy to understand tag.

     The greatest change for carpenters is in the hardware required to connect these new copper-based pressure treated lumbers. This new wood is much more corrosive to fasteners than CCA. Do not use nails, screws or connectors that are labeled “galvanized” as these well start to corrode in just weeks. At a minimum, use fasteners labeled “hot-dip galvanized.” Your better choice is to use stainless steel screws and bolts Type 304 or 316. Some screw manufacturers claim their zinc galvanized coatings although not hot-dip are usable on all pressure treated woods. Be sure to ask if they warrant their use before committing a major deck or wall project to questionable fasteners.

     Polymer-coatings may be a viable alternative, but so far none have gotten the nod from the ASTM (American Society for Testing and Materials) for use in the new pressure treated lumbers. Some independent labs have confirmed the performance of these polymer coatings. Again, look for the warranty.

     Joist hangars, post anchors and other hardware need to be considered as well. Look for an ASTM label that says they conform to ASTM A653. Two lines you can find on the market today are the TZ line from USP and ZMax from Simpson Strong-Tie. As stores transition to these new lumbers, finding the right connectors may take time and planning. Marine and coastal suppliers will probably have what you need as they are accustomed to selling to people building in a corrosive environment.

     Lastly, you cannot use aluminum flashing. It will start to corrode immediately. Look for copper, galvanized or membrane flashing. While not specifically noted in any of the research materials used in developing this article, it should be assumed that some compatible flashing will need to be placed between any pressure treated wood and aluminum siding to prevent rapid degradation of the siding.

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To make the new preservatives effective, their copper content has been boosted substantially -- from around 18% to 96% in some cases. Because ACQ and copper azole contain so much more copper, you can expect to pay from 15% to 35% more than you paid for CCA lumber. The cost varies because the amount of chemical treatment varies. CCA wasn't that expensive, so most CCA lumber was given a maximum dose of preservatives and rated for ground contact.

To keep down the cost of the new pressure-treated wood, manufacturers will produce different levels of protection (chemical-retention levels) for different end uses (see More choices than before). End-use categories will be marked on the tags stapled to the end of the board, but in general, they'll be determined by the dimension of the lumber itself. The lowest chemical-retention level will be for 5/4 stock, or decking. One level higher will be 2x lumber, or above ground. Ground contact will be 4x and 6x lumber, and other stock will be treated for permanent wood foundations (PWF, or structural members).

Although most of the time this system of categorizing chemical-retention levels will jibe with the actual end use, a reasonable potential exists for accidental misuse. You need to make sure you're using ground-contact lumber if that's what you need.

More copper makes the new pressure-treated wood more expensive. To reduce costs, companies are offering lower levels of treatment (retention levels) than before. Through scientific testing, the American Wood Preservers Association (AWPA) sets standards for retention levels based on end-use applications. The building code approves the standards, and a third-party inspector verifies compliance by wood treaters. You'll find this information on a tag stapled to the lumber.

Use corrosion-resistant nails and joist hangers

Unfortunately, boosting the copper content in lumber not only makes the new pressure-treated wood more expensive than the old, but it also makes the new stuff significantly more corrosive -- 5 times more to common steel, according to American Wood Preservers Association (AWPA) test results.

Most people already know that they should use corrosion-resistant nails, screws, and connectors when they're building with pressure-treated wood. But now the stakes are higher. Due to the high risk of galvanic reaction between the copper-impregnated wood and any dissimilar metals, fasteners and flashings should be stainless steel and copper whenever possible. At the very least, you need to use better grades of galvanized fasteners. Unfortunately, the fastener grades aren't always marked on the boxes of nails and screws.

Electro-galvanized stock is rated with a class scale that ranges from 5 to 110. Hot-dipped galvanization ratings are based on the actual weight of the coating. For example, a G-60 rating means that there's 0.60 oz. of zinc per sq. ft. of metal.

The G-60 and G-90 hot-dipped coatings are what we've been using until now. But engineers suggest stepping up to the heavier G-185 coatings for hot-dipped galvanized products, and they recommend class ratings of 40 or above when using electro-galvanized fasteners, such as expansion bolts.

Currently, G-185 is the best galvanized protection that you can buy. Simpson's ZMax line and USP Structural Connectors' Triple Zinc line both are rated at G-185. As for nails and screws, many of the composite coatings that are currently available are still good for the new treatments (see www.osmose.comto read about fastener recommendations), but you should verify this by carefully reading the label.

Corrosion dangers require better flashings, fasteners, and connectors

The new pressure-treated wood contains high concentrations of copper, which could quickly corrode the critical flashings, fasteners, and connectors where the house and the deck meet the foundation walls (or floor slabs). Clearly, these dangers will be greater in regions prone to hurricanes, tornadoes, and earthquakes. The solution is to use stainless steel, copper, or better grades of hot-dipped galvanized.

The weak links in the system with the new treatments are instances where there's a significant chance of using the wrong fastener or flashing. Deck flashings will have to be either galvanized or copper.

Pressure-treated bottom plates in slab-on-grade construction also offer weak links. Cumulative effects of corrosion could be catastrophic in tornado and hurricane zones. Will production-framing crews meticulously switch to galvanized nails when nailing studs and sheathing to the bottom plate? And what about foundation anchor bolts, which attach pressure-treated mudsills to basement walls? Galvanized versions are made, but they aren't commonly available.

Nails for powder-actuated tools and retrofit expansion bolts have a zinc plating, but their electrogalvanizing may need to be boosted to a higher class rating. Engineers at Ramset-Redhead say it's too early for their corrosion-test results to show a trend.

The wood still needs to dry before you can stain it

Most water repellents can be applied immediately to the new pressure-treated wood, and some manufacturers offer a water-repellent treatment as an upgrade. But manufacturers still recommend an additional level of protection. The wood preservers group suggests waiting for the lumber to dry before applying an oil-based semitransparent stain to the new varieties of pressure-treated lumber. How long you should wait before applying the stain varies depending on where you live. In New Mexico, you probably should wait for six weeks; in New Orleans, six months would be a more preferable length of time.

Borates may be better

Not all pressure-treated lumber is copper-based. Borate-based treatments are also effective at stopping bugs, mold, and rot. Borate lumber treatments have low toxicity levels for people and pets. Borate taken into the body doesn't build up like heavy metals do; our bodies excrete what they don't need.

Borate pressure-treated wood has excellent to outstanding corrosion resistance to common metals, according to standards established by the AWPA. No special fasteners or flashings are required.

Lumber treated with disodium octaborate tetrahydrate (DOT) historically has been used in protected, not exposed, locations because borate leaches from wood when the wood gets wet.

But studies show that borate-treated lumber doesn't leach as much as its reputation suggests.

And borate treatments are getting better. Wood Treatment Products Inc. (www.eswoodtreatment.com) has developed a way to fix borate into lumber better. EnviroSafe Plus is the brand name of this turbo-borate, and it has tested well for borate retention, noncorrosiveness, fire suppression, and nontoxicity of smoke.

Safe handling and use

The safe handling and use of CCA-treated wood—or any other material that contains hazardous chemicals—is simple. Please read the following tips:

• Never burn treated wood.
• Wear gloves and long sleeves when handling treated wood. If your project includes cutting or sanding, wear eye protection and a dust mask, and work outdoors.
• Wash hands after working with the wood and before eating or drinking.
• Do not use treated wood where it will come into direct contact with food (e.g., cutting boards).
• Do not use treated wood or wood scraps where they could enter the food chain (e.g., feed storage, silos, water troughs, compost, mulch, wood chips).
• Avoid using deck bleaches and cleaners on CCA-treated structures, as these may affect the release of wood-preservative chemicals.
• Some studies suggest that applying penetrating coatings (e.g. oil-based, semi-transparent stains) every year or two may reduce the migration of preservative chemicals from CCA-treated wood.
• Contact your local or provincial government for information on how to properly dispose of this material in your community.