Low level deck with slab

[smokocw]

I recently had a patio installed and want to complete the feature with a 5.4mx3.8m deck.

There is an existing 3.3mx3.3m  ~100mm thick slab as shown which is about 1/2 of the deck area to be built over.

Clearance from the slab to proposed deck floor level is 100mm (at the door) to the internal floor tile level

For the remainder of the area is a clay "soil"

My questions here are can I build a deck on top of the existing slab with only 100mm clearance?

Is there a minimum size for joist requirements ?

Will I need to dig out the non slab area to a certain depth ?

The Deck will extend out to the gutter on the sliding door side beyond the existing slab

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

[Jason]

Hi @smokocw,

Looks like it will be a great area to enjoy the warmer weather. I'm sure Workshop members will be happy to assist with your decking project. If you search for low level deck here on Workshop you might find other projects of interest from other members as it's a popular topic. 

Welcome to Workshop. We're pleased to have you join us and look forward to seeing how this project (and many others to come in the future) progress to completion. Feel free to post anytime you need assistance or have something to share. 

Jason

[DIYDave]

Following with interest. This might help.me in the future as I have simular issues.

[MartyH]

@smokocw 

Is the slab we can see in the picture connected to the house slab? 

[Itai]

Hey @smokocw 

Great patio. This is a future project I want to look at for my home Reno if budget allows.

Could I ask what the patio set you back? Did you have to go through council?

Was it an off the shelf type patio, like the ones at stratco, or custom built?

Thanks

Itai

[ProjectPete]

Hi @smokocw 

Are you installing a timber or composite deck? I ask because they have different clearance requirements. Timber should have 300mm to allow sufficient airflow and help keep the timber as dry as possible. Composite you can get away with the 100mm in that slab area without any issues.

Joists should be a minimum of 120x45 H3 generally speaking. So, I'd be installing 90x45 H3 timber for the framing above the slab, then move to 140x45 (bearers) and 120x45 (joists) for the remaining without slab. The frame would be supported by 100x100 H4 stumps at least 300mm deep.

Hope this helps - happy to help some more if you like.

[GailM]

Hi All
Am excited to see similar deck options to the area we would like a deck.. There is currently a small slab we would like to extend and your tips and guide is a massive help.
Will be staying close to these posts.
Thanks for all your information..
Will be sure to post our soon to be deck when we start.
Looking forward to further tips and photo's shared.
Thanks heaps
Gail

[Jason]

Hi @GailM,

Welcome to Workshop. We're really pleased you could join us and look forward to seeing your deck project come to life.

I would recommend you start by having a look at our Top 10 most popular decking projects for some inspiration, as well as the very recent backyard makeover by the @MakeItYours team.

I'd also suggest you start a new discussion and share some photos from a few different angles of your area so members can get a better idea of what you are working with. We have an amazing community of clever and creative people sharing advice and inspiration every day, so I'm sure they would be happy to help as much as possible.

Thanks for joining in the discussion,

Jason

[GailM]

Thank You for messaging me back...

Andrew and I are keen on ideas to get started on planning the upgrade of our area out the back..

Seeing other peoples projects is a huge help- although we are now coming up with other ideas and changing our minds often.. Quite fun and exciting actually..

Andrew will measure up and take photos of area over this weekend for me to upload here..

Looking forward to more ideas and comments.

Thanks again

Gail

[pete_brig]

Hi @smokocw  (cc: @GailM @DIYDave @Itai ).

Couple of comments from a untrained handyman--I was going to say jerry builder but I use good materials & overengineer  

• Here's a link to my project "yard reno" and update photos.  (plants r suffering with the current heat & lack of rain). Don't let the size put you off--the principles are the same & a bigger area just takes more materials & time to complete. The smaller deck took 2-3 days &, like most projects, most of the time was in the prep--setting levels etc. 
• As per @ProjectPete, th size & number of joists, bearers etc is important for structural integrity--these depend on the span (distance between supports) & spacing. Span tables can be found on some websites but I use a manual ("The Australian Decks & Pergolas Construction Manual", Allan Staines).
• Both decks butt up to the house slab of the al fresco area--I bolted bearers to the slab.
• I "simplified" my job by placing H4 treated timber directly on the ground--I figured they'd outlast my time at this property. I used sleepers for the smaller deck & fence posts for the larger deck. The earthworks ensured I had "reasonable" clearance for ventilation & drainage.
• Finished both with treated pine to keep the cost down (about half the cost of our preferred merbau) & then stained (merbau colour). I expect that the cost of bought to measure timbers would be cheaper than a decking kit  system (e.g. Good Times Decking) but the labour is probably more. Pays to do the sums

In summary: while your project won't be as quick or as easy for the chippies for the Backyard makeover  most things are possible with planning/research followed up with blood, sweat, tears, & patience!   Happy to provide info.

Cheers, Peter