What joist size to use for low-level deck?

[Zog]

Hi everyone. I have assembled the framing of the modular decking for my low level deck (see photos). What is in the photo is essentially a walkway, the main deck will be under the pergola and slightly higher. I've gained some confidence from what I've done so far and am considering using tuffblocks and building a framework rather than using the modular decking for the main deck. My question is just about the joist size. I'm not going to use a bearer and joists system, just a framework of joists, mainly because the Pergola is already there (before I bought the house) so I need to preserve the ceiling height of the pergola as much as possible.

I'm unsure about joist size and span of tuffblocks. The Tuffblock website has an article where they're using 2"x6" (45x150) joists, I've seen joists of 45x90 used in Australian based articles and the joists of the Good Times modular panels from Bunnings are 45x70. I'll probably use 140x19 merbau decking.

The pavers will be staying, they're not perfectly level, a small part of the deck will be on soil (the far sides in the second photo).

The total size of the main deck will be about 6.4m x 7.4m or 47.36 m2. It's a lot bigger than any articles I've seen about building a  low level deck. Any advice will be much appreciated.

[Zog]

Hi guys,

I'm on the last stage now, the walkway is finished and the 140x19 merbau deck boards were delivered.

Is 2 screws per joist sufficient to screw down the 140 wide boards ?

[EricL]

Hello @Zog 

Yes, two screws per joist are standard for 140mm-wide merbau decking boards. This ensures they are properly secured and minimizes the risk of warping or cupping over time. I strongly suggest using a P&N 10G Quickbit TCT Cut Smart Countersink Drill Bit to save you time when drilling and countersinking the holes for your decking screws. This has an excellent review from the deck builders that have used it. My best advice is to test the drill bit first on timber offcuts so that you can get familiar with its function and behaviour.

If you have any other questions we can help with, please let us know.

Eric

[Zog]

Hey guys,

I've been using the Simpson Strong-Tie hardwood to softwood 12g x 50 no predrill screws for the decking boards.

I've already been through 3 boxes (250 screws to a box) and estimate I'll need another 5 boxes which is another almost $400.

I couldn't find any boxes with more than 250 screws at Bunnings.

Can I just confirm whether there is a bigger box that's more economical ?

 

[JacobZ]

Hi @Zog,

The Simpson Strong-Tie DHSD screws are available in boxes with a quantity of 1100.

They are, however, not kept in stock and will need to be special ordered.

I'd suggest giving your local store a call and speaking with the Special Orders team, who will be able to assist you with a price and ordering. For 50mm screws, Simpson's internal product number is SSDHSD50TR1100, for 65mm screws, it is SSDHSD65TR1100.

Let me know if you need any further assistance.

Jacob

[Zog]

Thanks