Well first let’s look at what some of the options are:
    •    Painted spruce (which includes pine and fir)
    •    Cedar
    •    Plastic composites
    •    Wolmanized® lumber
    •    Chromated copper arsenate (CCA)
    •    ACQ-treated wood, which is alkaline copper quaternary
    •    Copper azole (CA)

But there are important issues surrounding these products, too, and you need to be informed before you decide on any particular type for your deck construction.

Also when you look at a wood preservative its important to remember that the treatment kills the food source for molds and fungus, but the wood will still absorbs water, swell, twist, warp, shrink and all the other great things lumber does. So don’t be surprised if the deck you build warps a little.

Painted Spruce
This includes all the spruce family, including pine and fir. These woods are very resistant only if they are allowed to dry. In other words, if water can get into them and not evaporate, they will rot from the inside out.
If you paint them always paint five sides and leave the bottom open so the wood can “breathe”. Decks that are open underneath and up away from the soil can be all right when you use this type of lumber for the joists.

However you should consider using a treated plank or decking for the top.

Cedar
Cedar is a wood that contains natural oils that resists funguses that destroy wood fibers. Cedar is also a very aromatic wood that gives pleasing smell when its wetted and dried.

Again, being wood it will absorb water, but it’s more resistant to damage when it’s allowed to get and stay wet. Remember though that it will also perform better if you ensure it can dry as well, so if painting, allow one open side, preferably the bottom, to allow for drying.

Chromated copper arsenate or CCA
This treatment is a combination of copper and a small amount of arsenic. Due to the uproar from the environmental lobby groups, the lumber industry voluntarily decided to remove this lumber from use for decks and areas where people would be in contact and possibly get slivers.

The wood is also used for PWF or preserved wood foundations. It is characteristically green in colour and has a pattern of punch marks that pushes the preservative deep into the wood.

ACQ-treated wood
The treatment is either alkaline copper quaternary or copper azole (with a Z not S!). It is forced into the wood under pressure, like a giant pressure cooker. These new preservatives are considered less harmful than the arsenic contained in the CCA wood, however they can cause a different problem.

They corrode metal connectors and fasteners more rapidly. That’s because the wood has an increased the amount of copper compared with wood treated with CCA.

The only acceptable fasteners are either Hot-dipped galvanized or stainless-steel fasteners. Regular screws and nails and aluminum fasteners are not. The new preservatives were twice as corrosive as CCA and can deteriorate in just one year!

Wolmanized® lumber
This is not a treatment invented by woman. This is a patented process for treating lumber. Traditionally it is a method of getting the preservative into the lumber without leaving those ugly marks on the wood. Often the wood will look browner than the traditional green colour.

Composite wood
This is a relatively new material, having been introduced just over five years ago. The material is usually made from recycled plastics and wood fibers. There are about ten manufacturers in North America.

You can get a variety of colours and sizes and they are usually resistant to ultraviolet light and moisture. Although they don’t warp and twist like natural wood products, they will tend to shrink over time. This is due to the plastic content and is usually minimal.

These materials can be cut and fastened the same as wood components however the cost is significantly higher than wood materials as well. The benefit being that its relatively maintenance free, as you don’t need to paint it.

So you’ll have to do some homework before you decide. Think about maintenance, lifespan, moisture and sun exposures. Cost can be an issue, but less if you are having the deck built and painted, rather than doing it yourself.

Just remember wood rots because it gets wet and can’t dry. Preservatives tend to kill the food source of the rot. Composite materials are environmentally friendly since they use recycled materials and are maintenance free.  

Darrell Paul, Building Consultant, has dedicated his entire career to the residential building industry. He is president of Building Science Resources, is a director with the Professional Home Builders Institute of Alberta (PHBIA) and is an accomplished speaker/presenter in addition to instructing home building and building science courses with SAIT.