The Pacific Northwest is beautiful. Much of that beauty is thanks to plenty of moisture, and climate conditions that are perfect for growing immense, lush forests. The trees that are harvested from these sustainably-managed forests make for impeccable building material—wood! Aesthetically beautiful, renewable, and environmentally conscious.

Unfortunately, the same conditions that grow our beautiful forests also create an environment perfect for the decay of wood. When wood will be used in applications that expose it to soil and/or moisture, only treated wood will last.

Dunn Lumber stocks treated wood available for applications ranging from above-ground, to ground-contact, to fire-resistant, all only using wood that has been treated with chemicals proven to be both effective for use and sensitive to the environment.

Most of our treated wood products have been treated with Copper Azole (CA-C), a copper-based preservative and an efficacious fungicide. The wood is ideal for applications including decks, retaining walls, fences, picnic tables, planter boxes, walkways, sill plates, and structural members. It is certified by Home Innovation Research Labs, meeting requirements for termite-resistant materials in the National Green Building Standard and by EcoSpecifier as a verified product.

It's easy to understand why some people have concerns about the safety of treated wood because they know there are chemicals involved. Arch Wood Protection makes the CA-C in the lumber we sell at Dunn Lumber. On the subject of toxicity: Arch shared that our treated wood is no more toxic than common table salt, and less toxic than the toothpaste with which we brush our teeth.

The three active substances in CA-C are copper, tebuconazole, and propiconazole. In terms of toxicity, the higher the number, the safer the product. For example, a low number would mean a lower amount could be ingested per body weight and still yield fatal results. The LD 50—or the toxicity of a substance—for each of the substances in the CA-C are:

  • Copper: > 5000 mg/kg
  • Tebuconazole: 4000 mg/kg
  • Propiconazole: 1517 mg/kg

If we return to our everyday comparisons, toothpaste typically contains about 0.3% by weight sodium fluoride as the active ingredient. The LD 50 for these two substances are:

  • Table salt: 3000 mg/kg
  • Sodium fluoride: 200 mg/kg

As can be seen, table salt has an equivalent toxicity to the actives in CA-C, while the active in toothpaste is significantly more toxic. Using the table salt example above, let's look at a typical man who might weigh 170 lbs (77 kg). It would take ingesting 3000 mg/kg x 77 kg = 231000 mg to receive a potential fatal dose. This is equal to 0.5 pounds of salt ingested at one time.

Plywood and some landscape timbers are treated with CCA, in a treatment process that has been used for many decades and is proven to be effective. When used in recommended applications, CCA-treated wood is harmless to people, plants, and animals.

At some of our stores we stock DRICON fire retardant treated wood. It is intended to be used in interior, weather-protected applications. It has a Class A rating, and is an effective and economical material for reducing the effects of fire. DRICON impedes flame spread and smoke development. The chemicals react with combustible gases and tars normally generated by untreated wood, converting them to carbon char, harmless carbon dioxide, and water. The wood is also useless as a food source for termites and fungal decay, thereby avoiding damage caused by these organisms.

We intend to always provide our customers with the best in building materials, including treated wood. If you have any questions about the process of treating wood, the substances used, or the lumber we stock, leave them in the comments below—or, as always, email me at