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Low level deck

Conrad83
New Contributor

Re: Low level Deck

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Thanks @Jason 

also wanting to query my bearers spans 

I’ve got 4  x 2/90x45 x 3.6m bearers spaced 1345 apart.

These are bolted to an existing concrete slab and then 2 stirrups in concrete footings . Spans are 1500mm.

Hopefully this ok?

It’s low level approx 150mm off the ground.

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Adam_W
Valued Contributor

Re: Low level Deck

Hi @Conrad83 & welcome!
Okay, just unpacking this a little...
With stirrups, single-sided especially, much of the load is supposed to be carried by the top plate of the stirrup, that is, your bearer needs to rest on the stirrup top. The load of the deck is then transferred directly to the upright of the stirrup and therefore the footing. This also means the load is evenly distributed directly downwards.

I suspect that the movement you are seeing is the vertical plate flexing with the present load. This will potentially get worse as the load increases with joists & decking.
This creates a number of issues I'd be concerned about.
- Movement may be an ongoing issue.
- This could stress the stirrups leading to failure (and the galvanising may come off leading to rusting).
- My biggest worry would be uneven loading. Instead of the load being pushed evenly down on the stirrup top plate it is being taken by one side effectively pushing or levering that side of the stirrup. This could cause them to fail.

If you cannot lower your bearers to them then I suggest that you pack it out beneath to fill the gap and transfer that load to the top plate of the stirrup.
These shims can be very useful & may be available thicker too or you could find some suitable timber to block in but it would need to be something that is quite solid such as hardwood or if treated at least H3, pref H4 with a good load rating.

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Conrad83
New Contributor

Re: Low level Deck

Cheers @Adam_W I’ll put some packers underneath. Just what your thoughts were on my bearer spans?

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Adam_W
Valued Contributor

Re: Low level Deck

Hey @Conrad83, in-short... there are quite few issues there.
- Normally 90 x 45 would only be used for joists, not bearers. A typical bearer size would be 120 or 140 x 45. Using a 'double bearer' structure will increase the load bearing a little but it's height, not width, that is most important. I assume to make that double-bearer you've used something like bugle-batten screws to join those 90 x 45s?

- That bearer arrangement without contact with the stirrup top is the reason why you are seeing movement.
- You have cut away the bearer at the slab end. That will fail (break) as you have reduced the load capacity by at least 50%. I would suggest you put stirrups up flush to the slab edge to support. If you need extra support you don't necessarily have to use more concrete & stirrups. You may find these work for you.

- You can build this deck with a 'bearerless design' by having a box of bearers around the outside then use hangers to support the joists across the centre with noggins between to stop them twisting.
I'm going to name-drop the always awesome @ProjectPete and ask him to have a look at your project too.
Stay tuned, we'll get you sorted!!!

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Conrad83
New Contributor

Re: Low level Deck

Hi @Adam_W yep have smaller 10 g

screws and a series of batten screws through them plus liquid nails.

I ended up putting two extra stirrups in on each bearer. Could get flush up against the slab as there’s a pip running near.

I’m a fair way into the joist now and seems very solid. Not getting any movement.

do you think it’s worth adding a row of blocking down each joist span?

Also what size screws and spacing would you recommend for 140x19mm merbau 

33F172D3-4A99-4522-B3BC-C4DA15F3C606.jpeg

on the end bearer with the half stirrups

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Jason
Community Manager
Community Manager

Re: Low level Deck

Hi @Harv,

 

Hope you are staying safe and well.

 

Do you have any pictures of the finished deck that you could share with the Bunnings Workshop community. Your project has been extremely popular with members and visitors to the site so it would be great if you could post the end result. 

 

Feel free to post anytime you need a hand with anything around the house and garden. 

 

Many thanks,

 

Jason

 

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