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Decking on concrete slab


Decking on concrete slab

Hi Guys,


Firstly I do understand there are quite a few discussions similar to this, however I am posting in hopes of getting a better understanding of what I need to do so I may avoid screwing up (disregard the pun).


So, I am wanting to build a deck on a new site over a concrete slab, the stepdown is 149mm, the concrete slab has a fall of 50mm. The area is 3290(L)x4180(W) there is a pillar which measure 470x470 as well. I have included a snippet of the drawing below.


How would you recommend starting this project, what timber and fixings would you recommend for the joists?

How would you suggest I raise the joists so I can keep it level with the FFL or would you suggest to leave room for expansion?

Is it necessary to fix the joists to the brick work? Would you suggest I place a frame around the joists?

Lastly more a question of vanity but how do you guys prefer to finish a deck, overhang, fascia, picture frame?


I do apologise for many questions, but i do look forward to hearing from you guys. 


Thank you.









Annotation 2020-07-06 223119.jpg

Bunnings Team Member
Bunnings Team Member

Re: Decking on concrete slab

Welcome to the Bunnings Workshop community @JJ01. Many thanks for your question, I'd be happy to assist.


It's fantastic to have you join us and we'd be excited to assist with your decking project. Initially, we'll need to address the fact that you have 149mm to build a deck within to end up flush with sills. Removing the decking board thickness from that height leaves us with 130mm to fit bearers and joists in. 120 x 45mm H3 treated pine can be obtained through our special orders service and would be a great choice for bearers as we can then leave a 10mm gap under them for water run-off and airflow.


Alternatively, you could construct the deck's bearers by doubling up Treated Pine Outdoor Timber Framing 90 x 45mm and I have given a rough estimation of the construction below. Given the joists and bearers are 90mm and the boards are 19mm, combining them comes to 109mm and we will need to make up the 40mm difference. The Eurotec 30-53mm Small Pro Feet Pedestal would be the perfect candidate as you can adjust them to counteract the fall over the slab. When you reach the outer extremes closer to the 50mm difference you can swap to the Eurotec 53-82mm Medium Pro Feet Pedestal as the small version will run out of adjustment height.


You do not need to fix the timber to the brickwork. However, considering the floating system of feet I have listed, if the brickwork is square, it would be a great starting point and will add rigidity to the overall deck. For finishing the deck around the sides a frame would enhance the appeal of it and could have decking boards placed over it. My personal preference for the final deck boards is a picture frame with mitred corners as it looks very neat and clean.


Please let me know if you need further information or had any questions.







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