When it comes to joists and bearers there are 3 main types to choose from. One being hardwood and all of its species, two being softwood and three being steel.
Hardwoods come in a variety of types and grades for all different applications however, most timber yards will supply the lowest grade of f14 for decks in Brisbane, they do this purely to be the lowest price but in doing this they are doing you no favours. F14 hardwood is a rough hardwood and very hard to work, it often isn’t very straight which makes the laying of a floor of your new deck very awkward. As a company we only buy F17 appearance grade timber, this is because it is always straight, clean and easy to work with and we always buy, when possible, treated hardwoods as I prefer the extra protection and it also means your new deck will last a lifetime.
Softwoods are being specified by a lot of draftsmen now days specifically in laminated materials called LVL (laminated veneer lumber). These are pine ply with an LOSP treatment; however they are not designed to be used as external joists as the preserving treatment washes out over time in the weather, this leaves a pine joist to rot out over the next year or two if it’s not retreated.
A deck built in Brisbane out of LVL’s will last a very short time unless it is built by an excellent tradesman with an in depth knowledge of this timber type and the owner does an enormous amount of ongoing maintenance, which is not something I would like to have to do to my new deck. I think this is not a good choice at all and it just goes to show the lack of experience and knowledge of drafts people and builders who use it as an external joist.
The other softwood readably available is CCA treated F7, which is pine. It can last extremely well outside but it has some inherent problems, as its low grade and you need to use large timber members to span short distances, also you have to use the correct hardware on it as nails from decking will want to lift out unless they have a twist or ring shank, however if they are installed correctly it can and will last a long time.
Steel being the final choice has never been my preference, I have repaired too many steel sections on decks from rust to be a fan and I find they are ugly, but in saying that there are some very good systems out there in steel, Duragal is one of them as it is electroplated not galvanised. Built correctly they will last a long time but one of their biggest drawbacks is decking has to be screwed down which takes a fair amount of time and they tend to be bouncy, but they are relatively inexpensive way for someone to build a deck.
We built, as a company, a few steel decks supplied and marketed by one of the larger patio companies but unfortunately we found them to be very poor quality and have decided not to build them anymore as we just can’t do them to the standard we would prefer.
How to choose
All of the above materials have their place in the market, but the problem I see is a lot of inexperience in their use. This causes the client a lot of problems down the track. We always prefer to build a deck with a roof as it will last a lot longer than one without. Any deck built by a deck specialist in Brisbane will normally outlast something built by the local carpenter or handyman, a deck built by a skilled tradesman should last a lifetime.