How to build a small deck using Decko footings?

[Samc1234]

I pan building a deck platform using concrete DECKO footings. The deck platform will roughly be 3.5m x 1.5m. I am wondering:

What will the frame structure under the deck look like?

What wood will I use for the frame structure?

What screws are best used when using merbau wood?

When placing the DECKO concrete, do they sit on gravel or do I need to cement them in?

How many DECKO concrete footings do I need for a high traffic area? (the deck will not have any furniture on it)

Thank you again, 

Sam

[EricL]

Hello @Samc1234 

Tamping will be enough, but if you wish to use crusher dust it is an option that is open to you. What's important is that the soil be as compact as possible.

Eric

[Samc1234]

Thanks Mitch, 

There has been an update to extend the deck to 2.4m

My questions would be: 

1. Do I need another row of DECK blocks as pictured?

2. Do I need beams (green) running horizonally as well? or would the yellow beam be enough?

Thanks

[MitchellMc]

Hi @Samc1234,

The yellow beams would be enough, but there is no support under the outside joists. Provided the supports are no more than 1000mm apart, you do not need additional Decko footings.

Mitchell

[Samc1234]

Thanks, so below is the updated version,

I have removed additional deck footings, on the DECKO guide it states that support will not be needed if they are close enough to the edge? is this correct?

In addition, do I need beam supports as seen in the red or not?

[MitchellMc]

They would likely be referencing the areas I've marked in blue @Samc1234. As long as the footer is near the end of the joist, the counterlever is supported. However, the joists I've marked in red are entirely unsupported. If you could imagine standing in the middle of those joists, they would bow down under your weight, as there is nothing supporting them. They are floating in the air.

Mitchell

[Samc1234]

Thank you, so if I put decko footings unde the red parts everything will work?

[JacobZ]

Hi @Samc1234,

In increasing the width of the deck to 2.4m, you would no longer be able to use the two deck blocks per joist that @MitchellMc recommended. To be in line with the Joist Span Tables, you would need to space your Decko footings no more than 1400mm apart, which will leave you with a cantilever of 500mm on each side, which is simply put, too large.

I've provided an explanation of what is generally allowable in terms of cantilevers in the discussion What spans and cantilever for deck? The allowed span for 90x45 timbers is 1400mm; 25% of this is 350mm, which is less than the 500mm cantilever you would require on both ends of your joists.

You have two options in this situation. Either add in a third Decko block so you can shift the outer two blocks closer to the ends of your joists, or use larger timbers such as 140 x 35mm H3 Treated Pine, which is capable of spanning 2300mm between Decko blocks.

If you make these changes and add Decko blocks to the red joists, then yes, everything will work.

Let me know if you have any further questions.

Jacob

[Samc1234]

Thanks Jacob, 

I think I will keep the two rows of DECKO and use the stronger timber and add footings to the red parts. 

The decko picture below includes timber that is 45 wide, will the 35 wide still be ok to fit inside the footings without moving?

[JacobZ]

Apologies @Samc1234, I wasn't aware of that.

It would be best to use 140 x 45mm Outdoor Framing H3 Treated Pine, considering that is the case.

Jacob

[Samc1234]

Thanks Jacob and that will allow me to still use 2 rows of DECKO blocks?