Low deck on TuffBlocks - do I need joist hangers?

djcowan

I'll start by saying this forum has proven very useful in helping me get this far. Thank you all kindly for sharing your experiences..
I'm closing in on trying my hand at a small alfresco deck.
The deck is over a concrete slab and will eventually 'L' around the house, extended along the top edge. So I am mindful of the distance for the top row of blocks and have pushed them as close to the current top edge as possible. (same distance as indicated by bottom row 190mm over hang)

Height to be under approx.1800mm to top of boards (merbau 18mm) - and TuffBlocks seem appropriate for footings. - I just don't want to see the blocks poking out underneath. (50mm Blocks + 90mm Joists + 18mm boards + 5mm for Klevaklips (?) and joist rubber etc) 

90x45 treated pine (M something approriate) for joists and "bearers", although the bearers aren't actually bearing any load.
I am unsure of:

1. whether or not to pin the bearer to the house, as doing so appears make it difficult to drive batton screws into the noggins which wrap the pillars.   

2. if the bearers - the boards running parallel to the house should be doubled up 90x90

3. or if I actually even need the bearers at all - I'm mindful of ventilation

4. if joist hangers are needed - perhaps for bearing the nnoggins? red circled areas etc concern me..

I am considering fewer tuffblocks between the central joists - increasing the span to around 900mm as I feel as though Im over engineering a fairly small alfrescco deck. 

notes: boards are spaced 5mm (ventilation) apart and framed with140mm merbau.

Sorry if this is a bit rambling- I keep remembering things and adding bits in.

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MitchellMc

Welcome to the Bunnings Workshop community @djcowan. It's wonderful to have you join us, and many thanks for your question about building a deck.

In a floating deck design like yours, there’s no need to connect the bearer to the house, as the deck isn’t reliant on the house for structural support. However, in the section at the bottom of your plan, where the extension lacks support, you’ll need to secure it to the house to ensure stability. Alternatively, you could add additional TuffBlocks or posts to provide independent support for that section.

For bearers supported at intervals under 1000mm, 90x45mm treated pine is appropriate, and there’s no need to double them up to 90x90mm. This sizing provides adequate strength for a small alfresco deck while keeping the design lightweight and cost-effective.

Joist hangers aren’t strictly necessary for your build, especially if you can secure joists or noggins directly by screwing through into the timber. However, they can be very useful in areas where this isn’t feasible, such as in the red-circled areas you mentioned. Joist hangers provide a strong and secure connection, ensuring stability, particularly for noggins or joists spanning longer distances.

Lastly, increasing the span between TuffBlocks to around 900mm is reasonable for a small deck like yours. It reduces material usage without compromising strength, provided the joists remain adequately supported. 

Please let me know if you have any questions.

Mitchell