Low-level deck for L-shaped alfresco area

Brad2022

Hi team, 

First time DIY for a deck and have very little experience so sorry in advance if I dont make any sense. 

I am planning on building a deck in my backyard shortly. I have read through some of the topic's already discussed in this forum but my situation is a bit different as I will be working with a concrete area and an L shape area that needs to be set with footings which I need guidance on and would like a better understanding on what I should be doing for my build. 

My tilled alfresco area is 4030x3135 and I plan on using (after reading some of the other forums to make the support stronger) 45x90 H3 timber as my step down clearance is only 75mm from our sliding door on to the alfresco, this will leave me enough to play with for levelling it off with window packers/shims (so we have clearance from the ground and we already have slope from the slab) and for the composite decking to lay on top. I have also read that dyna bolts are a pain to deal with and I should be using Anka Bolts? Am I heading in the right direction? how far apart should I be putting an Anka bolt into the joist, every 500mm?

Now to the right and in front of the alfresco is my landscaping area that I need to set footings. Now when I work out how much room I have to work with its around 270mm to the bottom joist on the alfresco. Can I have a stump that is only 125mm from the ground with a 145x45 bearer sitting on top with the 45x90 joist running across the bearers or should I be using 75x45 joist and reduce the height of the stump by 30mm to 95mm? 

When running my joist from the alfresco (joist are being laid away from the house with the decking running left to right) is it good practice to run it the full way from the alfresco to the landscaped area where the footings and bearers will lay or would I do this in 2 sections? 

How long can I run a bearer before I have to make a join on a post as I need to set footings, post and bearers for about 8000mm before coming into a tight 840mm gap. Unsure how to go about the 840 gapping as I don't think I can put 2 footers in...

I have uploaded pictures and a drawing of my backyard for a better understanding.

Thanks,

Brad 

MitchellMc

Welcome to the Bunnings Workshop community @Brad2022. It's wonderful to have you join us, and many thanks for your questions about building a low-level deck. 

If you haven't already read through it, I'd recommend you check out @Adam_W's article on How to build a low-level deck. Building a deck within 75mm would be considered extremely low. There's no room for airflow under the deck, and you should expect the lifespan of the timbers used in the deck to be reduced from early decay.

Ankabolts a certainly an alternative to Dynabolts. Fixing your joists down every 1000mm should be sufficient.

It sounds like having a 140 x 45mm bearer and the joists sitting on top would be the best option. 90 x 45mm is just about the minimum you'd want to use on a deck.

If you can, using joists that span the entire length of the deck would be best. I can't see any real benefit in constructing the deck in separate sections.

The dimensions of your bearer determine how far it can span without support. The 140 x 45mm can span at least 1000 - 1200mm before requiring post support. It likely can span further, but you'll need to reference timber span tables to find out the max span.

I'm really keen to follow along with your project, and I trust our members will be looking forward to assisting as you go. Please let us know if you have further questions or get stuck.

Mitchell