How to build low-level deck over a concrete slab?

[Ginger1]

Hey team and community, 

I've been enjoying reading other brilliant posts on this topic and I have learnt a lot but still need some 'yay or nay' input for the plan I've put together to get some confidence and feedback. 

I'm planning to build a low level floating merbau deck with a picture frame over the concrete porch out the front. 

The final deck height is 140mm from the ground so I'm avoiding sitting the joists on bearers and instead I'm going to connect the joists to a wood perimeter using a combination of joist hangers and pedestals for support underneath.
The reason for the perimeter vs just having perpendicular joists to the house is for structural support, picture framing the outside and I'm under the impression I need joist hangers as the pedestals won't suffice on their own. 

Materials so far:
90 x 45mm Outdoor Framing H3 Treated Pine 

90 x 19mm Merbau decking

And then use the Builders Edge Minifoot Pedestals to cover the remaining 31mm and allow the final deck height to be in line with the entry way brickwork.  

Pryda Joist Hangers for 90 x 45mm

I've attached photos of the space as well as a mock up of my design for the frame so far. The deckboards will run parallel to the house so my joists are all perpendicular to the home. 

Some questions I still have:

-  Anything missing from the plan? 
If I'm overthinking it or (more likely) underthinking some part I'd love to hear about it.

- Should I move the pedestals to the edge?
In my drawing I've placed the pedestals (grey boxes) under the joists. As I am going to use joist hangers as well, I'm thinking it makes more sense to place the pedestals under the perimeter wood so all parts of the structure are supported. Of course, for the longer spans in front of the entry I know I will need pedestals under the joist there too for support. 

- With fixings, what would be ideal for connecting the frame together and also for the decking boards?
I was looking at Zenith 10 - 8 x 75mm Treated Pine Countersunk Head Screws  for the frame. For the deck boards I'm not sure what would be a suitable option.

Area for deck:
     

     

Deck design so far:

Thanks in advance for any input!

[JacobZ]

Hi @Ginger1,

Welcome to the Bunnings Workshop community, it's great that you've got such a well thought out plan for your upcoming decking project.

Having given your plans a thorough look, I have to say I'm quite impressed. The only thing I might consider, and it is because I tend to over engineer everything, is exactly what you've already said, move the pedestals to the edge and maybe add 2 more to the longer spans running off of the door. Everything you have is well within the recommended spans for the timber you've chosen, I just like to have peace of mind that any project I undertake will be standing strong for years to come.

The screws you have selected are perfect for this application and will provide good solid connections for your joists, the only issue I see with using these is that they couldn't be used for any joist hangers as they'd punch out the back of the timber. Having a couple of different lengths of screws is always handy on decking projects, I'd advise a box of Zenith 8-10 x 30mm Tufcote® Countersunk Rib Head Treated Pine Screws alongside the ones that you've selected for the frame. I would then use Buildex 10 x 50mm 8TPI Climacoat Coating Decking Screws to fix down the decking boards. It might also be handy to get one of these Macsim 10g Clever Tool Standard Head - Blister Pack as they make the job of predrilling and countersinking your screws a breeze.

If you have any further questions, don't hesitate to ask and please update us as your project commences. 

Jacob

[Ginger1]

Hey JacobZ,

Massive thanks for the reply. Hoping to make a start on the weekend, weather permitting.

Adding the extra pedestals in for the spans running from the door is a good idea, I agree with your overengineer sentiment so I avoid creating more work for myself later. Appreciate the clarification around the screws as well. That clever tool looks super handy and will defs add it to the list. 

Will post an update once things get under way.

Cheers!

[JacobZ]

Hi @Ginger1,

I'm very excited to see the finished product.

If you run into any issues, don't hesitate to reach out.

Jacob