Low level deck

[Harv]

I am building a low level deck and I’m restricted with height.

I’m using 140x45 H3 treated pine bearers.

I put my posts in at 1.8mt spacings. The deck is 7m x3.6m with flush joists and centre bearer. Now I’m not sure if my stumps are too far apart for that size timber.

Community manager's note: Check out How to build a low-level deck for expert advice.

[Johnny]

 So this is where I’m at on the deck. Im just wondering if having this as the last bearer is ok, and let the joists overhang by approx 500mm? TIA

Johnny

[BIM_Engineer]

@johhny
Thanks for the photo
Place the bearer roughly in the same location as it was previously
from the end.( Cantilever Should be less than 10% of the back span)
Bolt( 2-M12 /joist) the extension joists over the bearer.hth

[Johnny]

@BIM_Engineer Thanks for that mate.

Another problem I’ve just encountered after digging a deep hole for one of the stumps is water slowly pooling in bottom of the hole, about 100 deep. I scoop it out but it refills.

I think this is due to the very soft foundation/soil right the way down as this is where our inground pool used to be a few months ago.

ive had to dig down pretty deep, approx 800, to hit relatively solid earth.

[BIM_Engineer]

@Johhny
When you filled in the pool hole did you compact the soil?
If not then excavate deeper to firmer soil
Thanks for the update

[Conrad83]

Hi @BIM_Engineer Ive done the same set up but with half stirrups and I’m getting some movement in the bearer. I’m guessing when I slot the joists in it will

tighten up but do you think this will be sound?

also my bearers are 90mm high so I have a gap under my stirrups (not sitting on the base) I think the vertical plate is about 110mm? Do you think this will work?

cheers!

[Jason]

Hi @Conrad83, many thanks for joining in the discussion. Let me extend a very warm welcome to the Bunnings Workshop community. It's terrific to have you with us. 

BIM_Engineer is no longer a member of this community. However, we have loads of helpful members who I'm sure would be happy to assist you with your decking project. Let me tag a couple of amazing contributors in @ProjectPete and @Adam_W who might like to kick off the discussion. I'm sure @MitchellMc will also be more than happy to help when he is back on the site tomorrow morning.

Please let me know if you ever need a hand getting the most from the site. 

Jason

[Conrad83]

 

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.

[Adam_W]

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.

[Conrad83]

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

[Adam_W]

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!!!