# Forum Home Renovation Decking  Low timber deck over concrete.

## Drumdave

Morning,  
I am building a low deck over concrete. Maybe 200 - 250mm high. It looks i can get away without doing bearers (I think) and just attach joists directly onto some sort of sadle.  
I live at the Gold Coast and went to some display homes for ideas. 
What one builder had done was use those metal rods with a thread and by the looks, drilled into the concrete, pushed in the rod, put a nut down to the bottom of the concrete with liquid nails at the base of it to hold it. Then at the top was a another nut underneath a metal plate to support the joist. 
These were spaced about 450 - 600mm apart along the joist and the deck seemed as solid as a rock. 
I thought this was ingenious for levelling the joist and only having to drill one hole for the joist support per sadle instead of two. 
Has anyone else done this method? 
If so did you drill into the joist so the rod goes into it a little. (I sort of imagine you'd have to.) there did not seem to be any glue or screws at the top plate though????  
Great web site, just found it this morning!!!!! Great stuff fellas! (Ooops and Gals) :Wink:

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## Pulse

Gee, that seems a good idea. They probably used a chemical anchor such as chemset to anchor the threaded rod into the concrete. The only problem is that this installation would have minimal shear resistance and  also should be fixed to the bearers in some way. 
thanks for your tip, and welcome
Cheers
Pulse

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## bitingmidge

Dave, 
Be careful!!   I'm sure if you check out all the construction codes in the world, you won't find any that allow a 12mm threaded rod to be used as a column! 
As Pulse says, the "liquid nails" is almost certainly (maybe not given the "bodge" description" epoxy (Chemset).  DON'T use liquid nails for this. 
ONLY pack under your joists with something solid, if you use the threaded rod trick,  pour little concrete pads around them to provide support and stability for the structure.   
While you won't have any uplift forces, the timber will move a bit, and from your description there's no way of tying it down, to stop the rattles occuring as it moves (and it will).  A couple of skew nails would be enough, but there's nothing to fix to! 
Lastly, consider how long the bolt will last exposed as it is.  The bit that will rust away quite rapidly is the bit at the base exposed to the moisture at the joint with the concrete, maybe 5years? 
Sorry to rain on your parade, don't do it! 
cheers, 
P (bodgy owner builders get all their ideas from bodgy builders!  :Rolleyes:  )

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## journeyman Mick

What BM said! 
What's stopping the deck from swaying back and forth or twisting? When you build any structure the trick is not so much in keeping it up, you can do that just by stacking stuff on top of itself. There's a lot more involved in keeping things from falling sideways or lifting up. Standard building practices exist because they're the most cost effective way to achieve an acceptable end result. As soon aassomeone works out a better way of doing things they patent it (if they can) and the whole industry (or a large part anyway) starts using it. Do it right, do it once. 
Mick

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## Drumdave

Thanks guys, 
It certainly seemed strong enough and there was no sideways movement in it. Not sure of the code of practise is on using these, but because the wait is distributed over such an area with the supports so close together seemed very rigid and stable. 
At the highest point the posts were about 250mm high with 75mm x 50mm josts. Agreed i don't think you would want to go over this height because of the small posts, but again, there was no movement at all. In actual fact, it looked quite impressive and well built. 
Rust.... yes good point, but could you dip them in something?? They were all gal by the way (rods, nuts. metal joist support plate looked like aluminium to me.)  
Do they make these threaded rod any thicker? 
If the consensus is not to use these.  
Is there any other plinth or cradle product that you can use when you only have 100mm to 300mm clearance for a deck over concrete?? 
Other decks had joists lying directly on concrete which wuld be far worse in regards to water rot etc. 
Thank you guys for the input it is much apreciated. 
It's great to have an Aussie site like this. I got sick and tired of the having to convert inches to metric on the Amereican sites!! 
Dave

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## bitingmidge

> snip... seemed very rigid and stable.

  for the time being!   

> At the highest point the posts were about 250mm high with 75mm x 50mm josts. Agreed i don't think you would want to go over this height because of the small posts, but again, there was no movement at all. In actual fact, it looked quite impressive and well built.

  Dave,  
Stop trying to talk us into it, it's not going to happen. 
See my post above, use the rods by all means, Personally, I'd use 200 square concrete blocks (half height - 100 mm), placed over the rods, backfilled with concrete and with concrete trowelled the last few mm to the required level.  You could use bits of 100 or 150 PVC pipe or anything else really, it's just permanent formwork that you are providing. 
Leave enough rod to go all the way through the bearer (_bearere_) and bung a nut on it. 
Why bearer?  Well you'll only need a few posts, instead of every 450mm, and in 250mm you've got plenty of space to set up your structural grid so that you can use 100 or even 75 Bearers and joists.   
Even if you built your supports every 1200 or so, it'd be overkill and a third of the work. 
You'll have a proper, level platform, done right with everything held down for the long haul.  

> Rust.... yes good point, but could you dip them in something?? They were all gal by the way (rods, nuts. metal joist support plate looked like aluminium to me.)

  Epoxy tar. 
If gal and aluminium are side by side, there may be some even more interesting results in a year or two!  :Wink:    

> Do they make these threaded rod any thicker?

  You can buy threaded rod any thickness you want, but it gets _extremely_ expensive.  

> If the consensus is not to use these.

  NEVER believe anything you read on the internet, not even stuff that Journeyman Mick writes, and specially stuff that I do! 
NEVER make a decision based on consensus, that's why politicians get it wrong all the time. 
DON'T do anything until you are convinced 100% of what is right.  (By the way, after reading this post you should be!  :Biggrin:   :Biggrin:   :Biggrin:  )   

> Is there any other plinth or cradle product that you can use when you only have 100mm to 300mm clearance for a deck over concrete??

   See above. 
All the best! 
P  :Biggrin:

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## journeyman Mick

> .........................................NEVER make a decision based on consensus, that's why politicians get it wrong all the time. 
> DON'T do anything until you are convinced 100% of what is right....................

  
Now Midge, you've just identified the other thing that politicians do and that's wait until they're 100% convinced something is right before they act. So invariably they commision studies, wait, debate, have another election etc etc etc, anything but make a decision. 'Cause if you don't make a decision, you can't make the wrong one  :Rolleyes:   
Mick

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## bitingmidge

Hmmm... you're right again dammit!! 
Well how about 85% ? 
P  :Biggrin:   :Biggrin:   :Biggrin:

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## Barry_White

Have a look here, maybe something like this might help you.  http://www.onesteel.com/images/db_im...20Brochure.pdf

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## Drumdave

OK OK the rod posts are out and i'm going for bearers with joists.  
Midge i'm not sure what you mean about this:    

> See my post above, use the rods by all means, Personally, I'd use 200 square concrete blocks (half height - 100 mm), placed over the rods, backfilled with concrete and with concrete trowelled the last few mm to the required level. You could use bits of 100 or 150 PVC pipe or anything else really, it's just permanent formwork that you are providing.

  I'm not a builder and not sure what you mean about backfilling the concrete blocks then trowelled the last few mm. I like the idea of the blocks. You do mean sitting the bearers on these with the rod attatching the the bearer to the block??  
I'm on concrete ( Tiled) and i have 260mm to play with for bearers, joists and decking height. The deck is 9900mm long (bearer length) and 3700mm wide. 
Thanks for the info Bazza will look into that as well. I can't believe there isn't a simple adjustable cradle for these low decks. Must be harder than I imagine. 
Thanks again.

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## JDub

> I'm on concrete ( Tiled) and i have 260mm to play with for bearers, joists and decking height. The deck is 9900mm long (bearer length) and 3700mm wide. 
> .

  IMO would just do as you have said and use bearers and joists, 
Use joist hangers and hang the joists in between the bearers (not on top) so they are the same level. Its more of a PITA to build but it will save at least 90mm of height and allow more clearance to the ground.  
Joel

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## Pulpo

The biggest Chemsets I have ever used were m20 which required a 25mm hole. 
As already mentioned you could get threaded rod very large, I have seen 50mm and I'm sure there is greater but have no idea of cost. 
But just remember you have to drill a hole in the concrete. 
Ramset also sell cartridge of epoxy instead of capsule which can fill any size hole but you also need their caulking gun.   
Could you do it the way you suggested, probably, would I? unlikely. 
Onesteels adjustable piers are great, have used those a few times. 
My understanding of Midge is the besa blocks are filled with concrete. 
Basically you are placing concrete around each threaded rod in the ground. 
But concrete needs form work to set in place. 
Its also mentioned not to have the concrete too close to the top otherwise the concrete pier maybe too high. 
Cover the end of the threaded rod with tape so the rod is clean for the nut. 
What was the size of the threaded rod used on the display homes? 
Good Luck 
Pulpo

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## Drumdave

Thanks for the replies. 
Hi Joel, three bearers with joists hung between them?? Yes sounds good and gives me back 90mm. 
HI Pulpo, Because the bearer will be resting on the concrete should I termite cap them. (If this is what you mean) Or do you mean still sadling them somehow to the post? 
The posts were only 12mm thick at the display home. I've definately given up on that idea. Going for traditionally built now. 
Regards, 
Dave

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## Purpleheart

> Morning,  
> I am building a low deck over concrete. Maybe 200 - 250mm high. It looks i can get away without doing bearers (I think) and just attach joists directly onto some sort of sadle.  
> I live at the Gold Coast and went to some display homes for ideas. 
> What one builder had done was use those metal rods with a thread and by the looks, drilled into the concrete, pushed in the rod, put a nut down to the bottom of the concrete with liquid nails at the base of it to hold it. Then at the top was a another nut underneath a metal plate to support the joist. 
> These were spaced about 450 - 600mm apart along the joist and the deck seemed as solid as a rock. 
> I thought this was ingenious for levelling the joist and only having to drill one hole for the joist support per sadle instead of two. 
> Has anyone else done this method? 
> If so did you drill into the joist so the rod goes into it a little. (I sort of imagine you'd have to.) there did not seem to be any glue or screws at the top plate though????  
> Great web site, just found it this morning!!!!! Great stuff fellas! (Ooops and Gals)

  G'Day Mate. 
We had a similar situation when we built our deck. 
We had a good roofed area out the back, but the concreted area underneath was really dodgy.  Little slabs which were all over the place. 
We ended up diging most of the crete out, but at one end where the concrete was pretty level, my Father in Law just made some brackets out of stainless which we bolted to the concrete, then bolted the joists to.  Then sat the decking on top.  It ain't goin' nowhere. 
Cheers...

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## Drumdave

Hi Purpleheart, 
Looks good. Out of interest, what was the distance between the brackets along the joist? 
Dave

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## Purpleheart

The brackets were a substitute for the last row of "stumps". 
They are on old concrete slabs which go back under the deck about  400mm. The concrete in this area was nice and even, the rest of the(previously concreted) area it was rather crappy, so it (the concrete) had to go. 
 In the picts, the deck is only about 100mm above the conc, but with the conc gone (under the rest of the deck) it is about 250 above the NS. 
If I had a level surface (of conc) to work with, and didn't want to build the deck too high, I wouldn't hesitate to use that method all the way through. 
Since I am not a builder, I tend to over engineer anything I build, and I spaced the joists at about 400, and the bearers were closer than spec too (but I can't remember now), but I knew I wanted to put some heavy things on the deck (eg Solid Ironbark Picnic Table). 
Another area of the deck had 25 stumps in a 3.5m sq area, but that was so we could put a spa on it. 
Cheers....

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## jonassen

> Morning,  
> I am building a low deck over concrete. Maybe 200 - 250mm high. It looks i can get away without doing bearers (I think) and just attach joists directly onto some sort of sadle.  
> I live at the Gold Coast and went to some display homes for ideas. 
> What one builder had done was use those metal rods with a thread and by the looks, drilled into the concrete, pushed in the rod, put a nut down to the bottom of the concrete with liquid nails at the base of it to hold it. Then at the top was a another nut underneath a metal plate to support the joist. 
> These were spaced about 450 - 600mm apart along the joist and the deck seemed as solid as a rock. 
> I thought this was ingenious for levelling the joist and only having to drill one hole for the joist support per sadle instead of two. 
> Has anyone else done this method? 
> If so did you drill into the joist so the rod goes into it a little. (I sort of imagine you'd have to.) there did not seem to be any glue or screws at the top plate though????  
> Great web site, just found it this morning!!!!! Great stuff fellas! (Ooops and Gals)

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## jonassen

g'day
YES IT IS A GREAT WAY TO DO IT 
I AM ABOUT TO BUILD A TIMBER DECK OVER A CONCRETE SLAB MYSELV
AND I WILL DO IT THE SAME WAY
TO HIDE THE NUT I AM CUT A SMALL SQAURE IUT ON THE TOP OF THE JOIST TO RECESS THE BOLT, SO THE BOARDS STILL WILL LEVELED

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## bpj1968

If you use dried treated pine F7 you can use  
90 x 35 joists.  These can span 1000 for a single span or 1300 continuos span (Over 3 or more bearers)
90 x 45 joists.  These can span 1300 for a single span or 1700 continuos span (Over 3 or more bearers) 
That's 110 mm used (Joists and deck) 
For bearers if you use 2 side by side 90 x 45 they can span 1200 between supports.  that gives a total of about 200 mm high.

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## Kyle

> If you use dried treated pine F7 you can use  
> 90 x 35 joists. These can span 1000 for a single span or 1300 continuos span (Over 3 or more bearers)
> 90 x 45 joists. These can span 1300 for a single span or 1700 continuos span (Over 3 or more bearers) 
> That's 110 mm used (Joists and deck) 
> For bearers if you use 2 side by side 90 x 45 they can span 1200 between supports. that gives a total of about 200 mm high.

  A good rule to use when building a deck is go 300mm less in your spans (ie. if you can span 1000mm. then only span 700mm).  While you use more bearers and stumps the deck ends up rock solid with no bounce. 
Also make sure the concrete your building on is good enough to handle it. Because if you need a permit the council may frown on you building on your old garden path.

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