How to build a low-level porch deck?

[devp]

Hi all,

First time building a deck for a first time home owner. I'm currently designing it (thankfully have some cad skills to lean on)

Dimensions as per attached. Yellow = frame (90x45 H3), cyan = joists (90x45 H3), blue  = Picture frame (140x19) red = decking timbers (140x19), purple = 90OD smallfoot pedestals.

Have designed for a 10mm gap between the rendered brick (In grey) and the frame as well as the rendered brick peirs. 5mm gap between boards and 19mm gap at outer edges for fascia.

Joists are spaced at about 320mm.

Sil to slab is 172mm, so presumably if I want the deck to be level it would be 172 minus the deck thickness (19mm) and minus the joist (90mm) leaving me with 63mm to fill with the pedestals (provided the slab is flat of course)

Is this is approprioate layout for the pedestals? I'm mostly concerned about the outer frame (in yellow) being unsupported, as I don't want to bolt that into the render. Do I need to use something else to support the outer frame or is it ok to just hang off everything else? 

[JacobZ]

Hi @devp,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us.

I've had a good look over your plans and have to say you've done a fantastic job. This will make a nice, solid deck.

The only thing I would change about your pedestals is the location of these two in the bottom corners. They should be moved to the first shorter joist between the column and the block wall.

 

With the outside frame, there are no issues on the left and right of the deck, as it can simply be screwed into the ends of your joists. On the right side, because you'll have limited access you may need to screw it on, then lift everything into place, or use angle brackets.

On the top and bottom of your plan, you would just add some blocking between the last joists and the outside frame. This can be done very simply by cutting some 100mm long blocks from your 90x45, then screwing them to the outside of your last joist at roughly 450mm intervals. You can then screw the outside frame to these blocks. With the one at the top, you would need to screw the blocks and outside frame to the joist before setting it in place.

Let me know what you think and if you have any further questions, please don't hesitate to ask.

Jacob

[devp]

Thanks Jacob, I was looking at a few examples with blocking and was thinking thats what I was missing!

Am I right in assuming I wouldn't need brackets like joist hangers or the like either? All of my joints would just be screws?

[EricL]

Hello @devp 

You do have that option of using large bugle screws for traditional fixing especially if you are not keen on using joist hangers.  

Eric

[devp]

So essentially all my fixing / joints would be a bugle screw either through the frame or through a joist?

[EricL]

Hi @devp 

It would be through the frame, the one thing that I did not see in your design is noggins. Will you be installing support noggins between the joists? 

Eric

[devp]

I wasn’t planning to if I don’t need them, would that just be to keep everything from twisting or buckling? 

[JacobZ]

Hi @devp,

Noggins would definitely be a good idea to prevent twisting and buckling.

As it stands, the only thing stopping those movements is the decking boards and the outside framing on the left and right of your plan. Decking boards aren't great at preventing those lateral movements, whereas noggins are.

They're a pretty simple way of adding strength and rigidity to your deck.

Let me know if you have any further questions.

Jacob