How to design hardwood deck supports?

[Krytie]

Looking to build a 6 x 7m deck using seasoned hardwoods (jarrah stumps and Karri bearers, joists and boards) reclaimed from a shearing shed but it's impossible to decipher the BCA regulations on how far the bearers can span, how deep the posts need to be inground, and whether or not we need bracing! In our shire it doesn't need to be a certified plan so we really don't want to pay for an engineer if we don't have to for what SHOULD be a simple project. Please help!

[MitchellMc]

Welcome to the bunnings Workshop community @Krytie. It's wonderful to have you join us and many thanks for your question.

If you can let me know the dimension of your bearers and joists I can show you a basic plan of how the deck can be set out to get you started. Although it seems like it should be a simple project it is a construction which is governed by the Building Code of Australia. This ensures that all decks built comply with a minimum safety standard.

You might like to contact your local council as often they will have their own requirements once again. How deep the posts need to be in-ground has to do with the soil type and stability at your location and once again the local council might be able to provide details on their requirements.

The best place to start is a plan and then you can look further into whether that plan complies with regulations. I'm happy to get you started if you supply those dimensions.

Mitchell

[Krytie]

Thanks MitchellMc.

I do have a plan, I drew it up from my understanding of footings from previous projects Luckily we've just owner-built so I had all the soil classifications etc, problem really was having unusual size timbers that aren't listed on the span tables easily findable online. And nothing relevant to our setup regarding bracing.

I did contact the council who have no requirements over the BCA code, luckily their building surveyor finally got back to me yesterday (we are in very rural WA so we don't have one at our shire, he works for a neighbouring shire and does the approvals for ours too so he's hard to get hold of lol)!. He looked up the tables for me and although our sizes weren't there he advised us that using spans given for the smaller closest size to ours would have to do without certified plans. That  works out to 1500 between posts and 1500 between bearers, 450 deep with a 100mm sole plate backfilled with sand not our clay. It's a bit of overkill but we have the materials onhand so it's not extra cost and only a few more holes in the scheme of things. Better safe than sorry!! Pretty happy with that actually as it's exactly what I had on my plans, apart from the sole plate as we were just going to concrete the posts in. Due to our huge posts and limited height off ground being just over 400 at the high side we don't need bracing, which is good news. Will be sure to post pics along the way.

[MitchellMc]

Hi @Krytie,

I'm glad that worked out for you. It's great that the councils building surveyor got back to you. Although your council doesn't have requirements over and beyond what the BCA recommends many places do. I know my local council has their own stipulations in regards to heights of decks and being able to inspect under them. I can understand your previous predicament as even when using standard sizing of timbers that the BCA mentions it still can be difficult to make sense of it all.

We'd be thrilled to follow along with your project and please do keep us updated on your progress.

Mitchell