What size steel for joists ?

[GAT]

I have recently completed an outdoor raised deck using Steel Deck and Eko Deck boards.  Stage 2 is to add a deck over the existing patio and flush with bifold doors - raising the deck about 90mm.

Plan is simply to run joists every 450mm with an edge beam attached to the house and attach these using dynabolts and brackets as the patio isnt completely level.

Question.  What dimension steel should I use for the joists ?  The distance/width of the deck is 4200mm and I was going to cut short steel blocks to go under the joists to level them.

Appreciate your help and apologies if this has already been asked.

[StevieB]

Welcome to the Bunnings Workshop community @GAT. It's fantastic to have you join us and we're always happy to help.

@Adam_W and @tom_builds may be able to offer advice here, as well as our resident D.I.Y. expert @EricL.

Look forward to seeing updates on your decking project.

Stevie

[EricL]

Hello @GAT

Thank you for sharing your question about what size do you need for your steel joists. 

Thank you for posting a picture of your decking project. Are you using Ekodeck for your follow-up decking project? If you are, you can deduct the thickness of the panel from your available space. For example, if your available space is 90mm, less 23mm which is the thickness of the decking panel. That leaves you with 67mm usable space. If you allocate 10mm for adjustment for height, that will then leave you with 57mm. 

If you are planning to use a Steel Deck System, I suggest sending your proposed plan to your store's Special Orders Desk to see if it can be built. I recommend asking a professional deck builder if it is possible to build it with the space available.

Let me tag our experienced members @tom_builds and @Adam_W for their recommendations.

Please keep us updated, we look forward to seeing your new deck built.

Eric

[GAT]

Thanks @EricL 

Yes - planning to use EkoDeck to match the new deck that only finished last week.  Just planning on running joists and brackets over the existing concrete patio so wanting to know what dimensions of steel would be recommended for the joists. Eg 70 x 50 x 1.6mm RHS

The height from the existing deck to the bottom of the doors from the inside of the house is 110mm so 87mm + the ekodeck boards.

I used the Steel Deck system for the current new deck as it was a fair way off the ground.

Thanks again.

[Jason]

Thanks for the extra detail @GAT.

@EricL will be back on the site on the weekend to provide his thoughts. Hopefully @Adam_W and @tom_builds will be able to share their opinion of your plan in the meantime.

Jason

[tom_builds · Accepted solution]

Hi @GAT,

The boxspan range of structural steel members has a joist range that are 100x50 x 1.2 or 1.6mm. Obviously for traditional joists you'd be choosing your size based on span, but by using steel members as battens you are able to fix them into the slab as often as you need in order to secure them. I'd say that 70 x 50 x 1.6mm would be fine, but maybe consider bumping up the thickness to 2 or 2.5mm to reduce the chance of the member twisting over time.

Hope this helps and best of luck with your deck project, by the looks of your other deck you are a quality operator.

[Adam_W]

Hi @GAT good advice all-round from the others.
It's a bit of an odd situation because you are having to increase the height. If it was a level install then battening it out would be just fine but as the joists will be increasing in height they still need to have the right spans etc. to avoid deflection of any sort.
When I had a tricky spot I dealt direct with the team at SteelDeck to explain my situation & needs & they then spec'ed it out allowing me to get a quote & then place an order through the Special Orders desk. I found this was a wee bit less confusing than explain to special orders, having them talk with SteelDeck, come back to me, back to SteelDeck etc.
At least that would give you a firm idea of what you need from a technical perspective.

[GAT]

Thanks @tom_builds  - exactly what I was after.  Really appreciate the help. !