Pressure Treated Lumber – What you didn’t know
treated lumber



Pressure Treated Lumber – What you didn’t know

​When building structures that sit outside in the elements it is advisable to use materials that resist decay and bug infestation - especially if they contact the ground or any other place with persistent exposure to moisture.

Some examples recommended by the EPA are:

  • Cedar
  • Redwood
  • Tropical Hardwoods
  • Plastics
  • Metals
  • Virgin Vinyl
  • Rubber Lumber
  • High Density Polyethylene

Obviously, each of the above recommendations has its pros and cons regarding costs, availability, and environmental footprint.

One additional substrate recommended by the EPA is ACQ Treated Lumber aka Pressure Treated Wood or PTW.

PTW reigns as one of the most commonly utilized material in exterior applications such as decks, fences, and small buildings. Why?

  • Cheap – when compared to the more durable options of Cedar and Redwood, the lower pricing makes it more enticing.
  • Attainability – Easy to find and largely stocked at big box stores or major hardware stores.
  • It works – PTW does what it’s forumulated to do.

But with the popularity of PTW, have you ever questioned what is done to the lumber to allow it to stand up to the elements in comparison to its untreated counterparts? Further, have you ever asked yourself,

What are the toxic consequences?

Let’s talk about what PTW actually is and what chemicals are used in this process.

PTW is lumber that is infused with pesticides, fungicides and other toxins and chemicals to give this substrate the ability to protect itself outdoors.

A process called “Pressure Treatment” is employed to force chemicals into the wood. The timber is placed in a chamber and chemicals are pushed into the wood by a vacuum and pressure system. This treatment does NOT protect the lumber from moisture.

The most popular form of PTW is CCA (Chromated Copper Arsenate) which, among other things, contain arsenic. This material was used for decades until 2003 when the EPA restricted the use of CCA preventing most manufacturers from treating lumber with the chemical for residential use (though it is still allowed in commercial applications).

The new form of PTW for home use is ACQ (Alkaline Copper Quaternary). This is a water based wood preservative that does not contain arsenic, but still includes the other chemicals as well as copper azole, copper citrate and formaldehyde.

ACQ has been adapted as the new standard for PTW. Though it is less harmful than CCA PTW, ACQ is still toxic and must be treated as a hazardous waste product. In fact, the following info can be found on the Material Safety Data Sheet (MSDS) for ACQ PTW:


  • Harmful in contact with skin
  • Causes severe skin burns and eye damage
  • May cause allergic skin reaction
  • Causes damage to kidneys and liver
  • May cause respiratory irritation
  • May cause damage to kidneys, liver, lungs, and nervous system through prolonged or repeated exposure
  • Very toxic to aquatic life


Additional things to note:

  • PTW is very combustible; wood dust may form explosive mixtures in the air if not properly ventilated.
  • The burning of ACQ treated wood will result in toxic fumes. This means that because of the chemical treatment you need to use personal protective equipment such as breathing masks and puncture proof gloves when handling it. Additionally, it needs to be disposed of as all other hazardous waste material – it cannot be placed in regular trash nor can it be used as compost.
  • As this type of lumber inevitably decays, the toxins stored within are released into the air and surrounding soil by a process called off gassing.


So if PTW is proven to be toxic; why do so many people use it?

Knowledge on its toxic side effects is not widely known. Most people whose occupations involve work with this material on a consistent basis probably have some kind of knowledge regarding its hazardous nature. The general public, however, is for the most part uninformed as to these health and environmental effects. Unless you take the initiative and do some research on PTW, chances are the average person will buy whatever is the cheapest option that will get their job done.

There are many green and safe alternatives to using PTW that provide the same (or better) results regarding durability and resistance to rot, mold, and insects. One simple way of circumnavigating the use of PTW is to construct with cedar or some other kind of naturally durable wood.

HoneyLove Architecture & Gardening chooses to not use PTW within our building or manufacturing processes. Our thought is that the solutions to constructing durable exterior structures are already naturally occurring in our environments so there’s no need to chemically alter the material.
Photo credit: Editor B / Foter / CC BY

Photo credit: Free Grunge Textures - / Foter / CC BY

Leave a Reply

Your email address will not be published. Required fields are marked *