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wanting assistance on a deck frame ive got about 200mm to work with before i have to start excavating,
deck is 3.3m x 8m
wanting frame to be low so there is airflow so bearers and joists are not sitting near ground
can the bearers be something like 90x45 x2 screwed back to back together then bolted/screw to some sort of steel stirup in a concrete footing ( steel footing brackets look to be way slimer then timber footings)
then joists would be say 90x45 every 450mm apart
can i use even 70x45 for joists and h4 square posts for bearers
OR
would it be alright to do single layer frame just using 140x45 timber
Afternoon @Trentc
Welcome to the Community of Bunnings 
Nice to se eyou in here and there are loads of decking questions plus projects you could have a look at to help with ideas.
Definently doable is the first part. Possibly without excavation tho it is close. There have been decks built with less space then yours.
I would sit down with a sketch book and draw up the overall area you want the deck to be,
Then figure which way you want the boards to run, aligned with the door or aligned with the wall on the side.
I like your second idea of a set of a "single layer frame, with closer joists being supported with half stirrups in concrete (You can go timber post as well)
As you draw all this up it will solidify what you want and also show what is needed.
This is a good link to understanding what is needed How to understand deck span tables
Factor in drainage for the area if needed, under deck lighting, power for elsewhere near the deck for power points/GPO's might be an idea to consider before the deck goes in.
A coffee, a sketch pad, pencil in a cafe and you have the perfect excuse to while away the morning
Dave
Hello @Trentc
Welcome to the Bunnings Workshop community. it's sensational to have you join us, and thanks for sharing your question about your decking project.
It's great that @Dave-1 has given you sound advice and has pointed you in the right direction. Just to add to the suggestions made, I recommend having a quick look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. These guides will give you a very good idea of how to plan your decking frame. Since you have 200mm of space to use, I suggest considering building a single layer frame with 90x45 along with Ekodeck which is 23mm thick. Which gives you a total thickness of 113mm and an air gap of 87mm.
In regards to footing, I suggest looking at the following:
- DEKO 250 x 150 x 150mm Instant Concrete Foundation Block
- TuffBlock 300 x 300 x 90mm Instant Foundation System Deck Support
- Builders Edge 70 - 170mm Bigfoot Xl Pedestal Feet
- 100 x 100mm 2.4m Fence Post Hardwood CCA
I also recommend having a look at the Bunnings deck building guide:
- How to plan out your deck
- How to set out a deck
- How to install stumps
- How to install bearers
- How to install joists
- How to lay decking
- How to add a step to your deck.
I also suggest having a look at this featured project - Low-level composite deck over concrete and soil by @oninpena. It's an excellent example of a single layer decking frame.
If you have any other questions we can help with, please let us know.
Eric
Hi @Trentc
If you were to build a traditional decking frame with bearers and joist 200mm of usable space would not be enough. For example, if the bearer was 140x45 plus the joist at 90x45 along with the decking panel of 19mm you would have a total of 249mm. You would have to dig deeper into the ground just to fit the frame. Even using a 90x45 for both bearer and joist would still not be enough as it would be touching the ground, and you would not have an air gap. If you were to use 70x45 as joist the air gap would be too small and would impact the airflow under the deck, plus it would severely limit the type of footing you can use for your frame.
I propose looking at the single layer frame for your project as it will not occupy all of your usable space under the deck.
If you have any other questions we can help with, please let us know.
Eric
