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So, you want to build a deck or fence...

 So, your deck is rotting or you need a new fence to keep the dogs in the yard. And, because you care about making good choices for the environment, not to mention your own health, it can be tricky to decide what materials to use.
Yes, we have all been there with these real-world dilemmas of what to do given your circumstances and budget, not sure what is the most sustainable option. Well, let's break it down. The main options for decks and fences are
  • pressure-treated wood,
  • naturally weather-resistant wood,
  • composite
  • PVC (plastic)
I'll start with the pressure-treated wood option as it is among the most common, and comes with some important considerations for health and the environment. You may have heard about the concerns with pressure-treated wood, that is because until 2003-2006 the green pressure-treated wood on the market was treated using a compound called chromated copper arsenate (CCA), which contains arsenic, a carcinogen, that was found to leach out of the wood and into the soil surrounding the wood, posing a health risk.
As a result, the use of CCA for most residential uses was restricted or banned in the EU (2003), Canada (2004), U.S. (2004), Australia (2006). However, some commercial and industrial uses remain permitted today and in the U.S. it is still permitted for residential shingles, shakes, and wood foundations.
What about the new pressure-treated wood?
Both brown and green pressure treated wood do contain copper and Health Canada advise precautions with both. Of the various types of treatments, one is the least likely to cause harm. This is called MCA (Micronized copper azole). With MCA the chemicals are added to the wood as a particle rather than with a solvent. This makes it less likely to have the chemical wash off and you have less off-gassing from MCA pressure treated. This is the dark brown version of pressure-treated wood.
Less corrosive to metals
MCA is also less corrosive to metals. With the other types of treated wood, ACQ and CA-B, both are highly corrosive to metals and you need to use hot-dipped galvanized steel nails to prevent corrosion of the metal. However, MCA is no more corrosive than natural wood.
Still use caution
However, with ALL pressure-treated wood Health Canada recommends precautions. In particular, do not inhale the dust, and do not burn the sawdust or off-cuts. The treated wood cannot come into contact with food-growing soils, or beehives where the bees may contact it. It should not be used for serving food, etc. You can check out this resource page to see the details and the various types of pressure-treated wood.
Naturally Weather Resistant Wood
Naturally weather-resistant wood is a great option (Cedar, as well as Larch and Hemlock), and purchasing FSC certified is certainly the most sustainable option here, and often available at major retailers. However, these woods tend to be expensive and may not perform as well as pressure-treated, particularly when in contact with soil.
Composite may not be as sustainable as you think
The key here is to think about the materials that are in that "Composite". Usually, this is a combination of plastic, often much of it recycled, but not all, and sawdust or wood fibre. Now, the unfortunate thing is that by combining the two you have something that can be neither recycled nor composted when you are done with it. So, while it has very good durability and ease of maintenance in its favour, the end-of-life question remains problematic. So, that plastic can go nowhere else in terms of recycling, and the organic matter of the sawdust is now bound up with it.
So, while it may look like a sustainable product I am not a fan as it has zero chance of going anywhere other than a landfill when you are done with it. In addition, the way it is constructed and held together impacts its durability and lifespan, and those components may deteriorate and fall apart more quickly than the decking itself, shortening the life of the deck significantly.
What about the shiny PVC materials?
Well, PVC is plastic, and among the plastics, it is one that contains, and releases phthalates, which are endocrine disruptors. These are the nasty compounds that interact with our hormone system by either mimicking hormones like estrogen or testosterone, blocking them, or altering their function. This is harmful to humans, especially during fetal development, and to other organisms. So, while we are not likely to have much exposure to this type of use of PVC, I think it's best to reduce the use and production of this harmful material.
So, in the end, my top choice is naturally weather-resistant wood like Cedar, Larch and Hemlock if it is FSC certified, that is, sustainably harvested. But, if natural wood is not suited to the project or your budget, any pressure-treated wood on the market is safe when appropriate precautions are taken. Don't inhale the sawdust and don't burn the sawdust or end cuts, and certainly don't allow the wood to come into contact with food. The safest type of pressure-treated wood is called MCA (Micronized copper azole) and is dark brown. You can find the type of treatment on the tag at the end of the boards at the retailer, and check the resource guide for all the details.
Either way, enjoying the outdoors is a great way to spend your time, so well done! Maybe while you are there you want to build a backyard composter or do some gardening. Find out here why gardening can make you happy. Enjoy!

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