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.

[JacobZ]

Hi @Zog,

Some curvature is expected when using softwood such as pine, in lengths as long as you are. 

It can usually be managed by pulling the curve out when screwing the timbers off but the hump that you've circled and curvature on multiple planes can be tricky to deal with.

You can often pull the curvature out when screwing the members off or cut them into shorter lengths for shorter sections of your framing. If you can use them in this way, this is certainly an option.

If there are any twisted lengths that you're unable to use, and they were from us, I'd be happy to put you in contact with a manager at the store of purchase to discuss options.

Let me know what you think.

Jacob

[Zog]

Thanks @JacobZ 

In that case I guess I can put the bent and multi-curved joists on the inside and I can use the noggins to pull them straight. I'll go ahead and get started and if I find that the two mentioned are unusable I'll get back to you.

[JacobZ]

Hi @Zog,

Sounds like a great plan. Remember to cut your noggins to the width the spacing should be, not what it is. Doing this means you can hit them into place with a hammer, which will straighten out the curves.

Keep us in the loop if you run into any issues, I'm sure we'll be able to come up with a solution.

Jacob

[Zog]

Hi guys,

I'm ready to install the decking boards to part of the deck. Because of the size of the deck (just over 400 mtrs of decking boards) I've decided to nail instead of pre drilling and screwing.

I know nothing about nail guns, I don't have an air compressor. The Ryobi 18v One+ 16GA Brad nailer looks suitable. It takes 16 gauge brad nails. Is it suitable for decking boards?

[MitchellMc]

Hi @Zog,

Brad nails are not suitable for fixing decking boards in place. They are like small pins and only suitable for light assembly project; they don't have the required holding power for decking boards. You would need to use a framing nailgun which uses much larger and thicker nails, but that's also not recommended as the readily available nails will rust as they are not treated for external use. You're best to screw the decking boards down. Regarding pre-drilling, that's not necessary as there are plenty of self-drilling screws available such as the Simpson Strong-Tie 12G (5.5mm) x 50mm 316 Stainless Steel DHSD No-PreDrill Hardwood To Softwood Deck.... There is no need to pre-drill; you just drive them straight in.

Please let me know if you have any questions.

Mitchell

[Zog]

Okay,

I'm using wooden joists, so it's timber to timber, not timber to steel. Are these screws still suitable ?

[MitchellMc]

Great catch @Zog! Sorry, I missed that they were timber to steel. I've updated the link above and suggest these Simpson Strong-Tie 12G (5.5mm) x 50mm 316 Stainless Steel DHSD No-PreDrill Hardwood To Softwood Deck... instead.

Mitchell

[Zog]

Thanks @MitchellMc , there are stainless steel nails though.

[MitchellMc]

There are some specialised Stainless nailgun nails out there @Zog. Are you referring to something like these Airco 50 x 1.75mm Stainless Steel Collated DA Brad Nails? If so, they are brad nails and not framing nails.

I'm sorry, but I am not familiar with anyone using stainless steel nails to fix down decking boards. Everyone I have dealt with uses screws or, in some instances, hand nails. I'm sure there are options out there, but I'm not familiar with any.

Mitchell

[Zog]

Okay. Another hardware chain has 2.5x50mm stainless steel nails with some threading in a coil but Bunnings doesn't stock them. But it seems that a framing nail gun is around $1000 anyway, so screws it will have to be. I'm just trying to not overestimate myself because 400+mtrs of decking boards is a lot of screwing and I'm not young. I'll just have to pace myself haha.