# Forum Home Renovation Decking  Very low deck over concrete

## cama

Hi Guys & Girls  Firstly I just want to say what a fantastic forum.   I want to lay a small deck (5 x 3) however there are a few road blocks I am faced with at the moment.   Firstly there is currently concrete laid where I want the deck to go with about a 70mm clearance to the top of the step into the house at the lowest point. The question is whether this is enough clearance to lay a deck in the first place? I would assume that it is if I was to use the concrete slab but there lies my second problem.   The second problem is that it looks like this particular section of concrete was put over the sewerage piping a little too soon after filling the trenches in so the slab has moves away from the house a little and has sunk slightly in places where the ground has compacted. This means that the slab is a little un even and has a considerable slop away from the house. This all means that I am a bit reluctant to just lay joist straight onto the slab because I am not confident that it won’t move in the future and the slop is a bit too steep to be comfortable with.   My current idea is to fix a bearer to the house with dynabolts and a bearer on posts just past the end of the concrete and then attach joists (I guess they will have to be about 45 or 50 mm) between the two using joist hangers. The question is though how do I support the joists on the slab? Do I just pack under the joists and not fix them to the slab incase it moves, if so with what? Or do I pack and bolt them to the slab? Someone suggested using threaded rod with a pad on the bottom so the height can be adjusted.   Any help with these issues would be great.   Thanks in advance and keep up the fantastic work.  :2thumbsup:

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## Twinadventurer

Hi Cama, 
A few pics tell a thousand words, but it sounds like we are in the same boat. 
Look forward to the responses from the experts here 
Good luck

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## DNL

Why not just get rid of the concrete slab? Sometimes getting rid of the problem is the best way to go. 
I used an Ozito concrete breaker the other day to break up a 6mx4m slab....it was cracked, loaded into a Kennards tipper truck which I hired for half a day and dumped at the concrete recyclers for $25. Truck cost $190 and the main part of the job was done in under 6 hours. 
Next day I scraped all the smaller rubble and cleared the site and took excess to the tip. I was tossing up with what to do with the concrete which was sloping and generally being a pain in the butt....in the end, I just took the view a clean slate was better to work with. 
Sounds like if you try a work around, it may pose numerous difficulties - which always seem to compound. For stability of the deck, I would fix it to the concrete, but from what you describe, this may cause you more problems. 
As Twin says, pics are the way to go 
cheers

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## Project1080

Hi Cama and welcome.
You probably have a couple of options available. 
1) remove slab altogether and start afresh
2) dynabolt treated pine lengths (say 90 x 45 mm) to slab then lay decking over these. Either put packers uner pine or cut pine lengths to allow water drainage.
Pine on slab is what i'm doing for my front verandah as it's the easiest solution.
3) cut squares out of slab for posts to go into then run joists past these and decking over.
4) Go with your bearer idea and cut squares in slab at other end for posts, then run another bearer across, Then put joists between the two bearers on joist hangers. 
With a couple of pics I might be able to come up with a few other ideas. 
Regards, 
Project 1080.

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## cama

Thanks guys for the comments. <O :Tongue: ></O :Tongue: > I would prefer to keep the concrete as i am not able to get anything wider than a normal doorway into the back yard to carry the stuff out. the slab also goes around the side of the house which i want to keep. <O :Tongue: ></O :Tongue: > <O :Tongue: ></O :Tongue: > You can see from the photo's that the slab has moved away from the house and sunk out near the garden. I am thinking of going with a bearer on the house and on posts just past the slab with dynabolts and TP spacers. Would i need to treat these with anything if they are going to be on the slab? I have attached a photo of what i am thinking about.<O :Tongue: ></O :Tongue: > <O :Tongue: ></O :Tongue: > Thanks again. <O :Tongue: ></O :Tongue: >

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## cama

Hi Guys 
OK well i have started building the deck. 
I have decided to dynabolt the joists to the slab and run a bearer just past the slab as my sketch shows.  
I have a few questions about stumps and spacer. 
Firstly since the deck is so low what is the best option for the posts that will be past the end of the slab? Should i concrete H4 TP posts straight in or should i attach post stirrups directly to the bearer? 
Also when it comes to the spacers on the slab will TP be ok or will it rot very quickly? 
Not sure what other options there are.  
Thanks again guys.

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## bpj1968

> I have a few questions about stumps and spacer. 
> Firstly since the deck is so low what is the best option for the posts that will be past the end of the slab? Should i concrete H4 TP posts straight in or should i attach post stirrups directly to the bearer?

    Eitheroption is good, attach the bearer, level, and then concrete post/stirup.   

> Also when it comes to the spacers on the slab will TP be ok or will it rot very quickly? 
> Not sure what other options there are.  
> Thanks again guys.

  Another option is plastic "Wedge it"    Basically wedge shaped plastic spacers and can fhold a lot of weight.  I got some recently from Bunnings (near the stirrups) and these would probably work.

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## cama

Thanks for the info. 
Plastic might be the way to go, i have never seen these before. Think ill make a trip down to bunnings.

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## cama

Hi Guys 
Well the deck is well underway now. I have finished most of the frame work however now i can see just how uneven the slab is. 
I will need to pack up the joist in 2 places along the slab giving it about 1m spans.
I am still a bit unsure of the best way to pack up the joists, as there is a large range in gaps and some are very large. The space between the slab and joists on the row closest to the house ranges from 20 to 50mm and the row away from the house ranges from 55 to 85mm.  
I was planning on using the plastic "wedgies" or "horse shoe" spacers with ether L brackets or a dynabolt through the joist into the slab. I am now a bit unsure because i think some of the gaps will be to large for the plastic spacers as they only come in 10mm at largest.  
What are my options? Any help would be great.  
Regards
chris

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## cama

Hi Guys 
Well i didn't get any replies to my questions so i sorted it out for myself. 
I thought i would post it on here if anyone is interested.  
I used the plastic Wedgies where the gap was small enough to use them (up to 35mm). 
For the others i found some bolt down stirrups at Bunnings that had an insert that kept the wood about 35mm off the ground. I bolted these to the slab and finished of the gap with small TP spacers. 
I did have to cut the top of some of the stirrups off as they would have sat higher than the joints. Other than this they worked perfectly.  
I am now up to laying the boards and its really starting to look like a deck.

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## dvdhack

Sorry to chime in late but if you still have concerns over the concrete moving further from the house, this is what I di in a previous house which is the same as your situation.  I dug a trench about 300-400mm deep around the oiutside edge and filled then filled that with concrete - I added some reo but that was just anal.  The beam acts as an anchor for the concrete - I also filled the gap between the house and slab to prevent water running under - used some silicon compound stuff - cant remember exactly what it was. 
Have fun

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## cama

Hi  
Thanks for the advice, i think that would probably fix the problem. I still need to dig a few holes for some posts (for a shade sail) so i might look into doing something similar to the trench you did. 
 I did fill the gap between the house and slab before i started the deck, though it would help.  
Thanks again

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## cama

Hi Guys 
Well just thought that i would give a quick progress update. I am almost done laying the boards, should be done tomorrow. The smart bit i am using is starting to get a bit blunt but should hold up.

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## Bloss

Cama - looks great - you'll love it when you start using.  :2thumbsup:  
Satisfying stuff when it all comes off even when it's a bit daunting and fiddly on the way!   :brava:

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## tipratrat

Looks great Cama, 
I'm looking at doing something similar (http://www.renovateforum.com/f196/low-deck-plans-88356/) and was wondering what size beam you used at the front (and near the house? ) to which you attached the joists? 
Also, what size joists are they? 
Also, on the section where this beam is over the grass, did you use posts concreted into the ground to support it? 
Thanks.

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## cama

Hi Tipratrat 
I used 70x45 for my joists as i was space limited against the house. The beam past the slab is just two 70x45 joist put together (would have been better to use 90 x 45 here because i had to pack it up in the stirrups). The wall ledger is also 70x45.  
I supported the beam by using post stirrups concreted in.  
I hope this helps.

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## cama

OK guys it is all finally done (just in time for the end of the holidays)  
It is not yet oiled (will wait a few weeks for that).
I ended up using the offcuts to create a feature on the fence to help give some privacy now that we sit about 100mm higher due to the deck. This worked well and i ended up with almost no left over timber.  
I have already tested it out with our first BBQ. Fantastic.

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## Jusso

Nice job, your deck looks fantastic. It looks like yours is suffering dusting foot prints just like my newly completed deck. I guess the virginess cannot last forever  :Biggrin:

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## Bloss

Ripper job mate - rewarding work ain't it!  :brava:  A disease that can be hard to shake though  -  the never ending reno story!  :Biggrin:

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## Pugsley

Hi Cama
i have the exact same prob. Any chance of a photo of the brackets and bolt down stirrups. Ive been searching for adjustable brackets for ages but cant find a thing. looks like u have my answer
Pugsley

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## courier

Hi Cama, How is the wood holding up is it rotting due to the height off the concrete ( similar problem here )

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