How to deck an area of this size to flow from alfresco over the dirt?

[MrSober]

So what started out as a simple deck covering our alfresco area has ballooned out to now add in the area around the alfresco also as I think it would just make for a nicer area once it is done.

I done a deck before but was only really over concrete so was a pretty simple one I found using KlevaKlips etc to get it all level and supported. No with this one spreading out over concrete and dirt I am having a little trouble working out what is the correct way to support the deck joists over the dirt, there seem to be a few different options but seems hard to find the pros and cons of each.

I was thinking to just have a one step sized step down from the alfresco to the deck over the dirt as this in my mind would make it a bit easier to get it all sorted and would mean I could finish off the alfresco part first and then do the other part later on. The Wife has put the idea of having it all level forward which I think could be a good option but also I am not 100% sure how I would achieve this.

Proposed area

How it all currently looks, kinda a mud pit which is other reason I want to get it sorted so I can get the draining in so it doesn't pool anymore.

Is there any specific product one might put forward of what to use over the dirt area to either get it the same level as the alfresco or maybe a step down.

[EricL]

Hello @MrSober

Welcome to the Bunnings Workshop community. It's a pleasure to have you join us, and thank you for sharing your question about your decking.

There are ways to achieve the transition from your cement slab to the soil. However, before you begin, I strongly advise you to level the soil area and create a slope going towards your backyard drain. I recommend putting in drain coils to facilitate proper drainage under your deck. Please make sure that the drain coils are not in line with your proposed footing area for the deck. I also propose putting in weedmat and drainage gravel to prevent puddles from forming under the deck. 

Once you've sorted out the drainage, I suggest looking at the Builders Edge Pedestal Feet. This footing in combination with pavers will allow you to cross over from the cement slab to the soil. The pedestal feet are adjustable and will give you precise control over the height of the decking frame. The soil will need to be compacted before laying down the paver and pedestal feet.

Doing a step-down is also a possibility and you can still use the pedestal feet for a lower deck. But I recommend doing a  single level as you get better air circulation under the deck.  

I propose checking your local council's rules and regulations regarding low-level decks before you begin your project.

Here are some good examples of a deck transition from cement to soil:

• Low-level composite deck over concrete and soil by @oninpena
   
• Low-level deck with steps and lighting by @asifkhawaja

If have any other questions we can help with, please let us know.

Eric

[Jason]

Hi @MrSober,

Let me also extend a very warm welcome to the Bunnings Workshop community. We are looking forward to seeing how you can transform your backyard and trust you will get lots of ideas, inspiration and advice from our helpful members. Please don't hesitate to post anytime you need a hand. We'd also love to see regular updates as you progress with this project. 

Let us know if you had any follow-up questions from Eric's advice. I would also recommend you have a good read of @Adam_W's popular guide How to build a low-level deck as it will give you an overview of the many considerations you will need to think about. 

Thanks,

Jason

[MrSober]

Thanks for the pointers, yes the leveling out was something high on the list with me spending some of this weekend doing exactly that getting alot of the low points filled in so drainage can finally be sorted. Just need some more

I was actually thinking something along the lines of the Uni-Pier etc either bolted down to a concrete footing or concreted themselves into the ground, but just need to get my head around the all the spans etc to know how I should lay out all the joists etc. then know how many all up I will need. Looking for something like in the example with the picture frame but with Blackbutt decking boards in the 86x19, I did my first deck in Blackbutt and love the wood. (might help that I still have some left over from the old project)

[MitchellMc]

Hi @MrSober,

Uni-piers could certainly be an option, though consider that the smallest one is 200mm. Do you have that much room to play with?

The basic principles are that your joists are laid at 450mm centres, and 90 x 45mm joists need to be supported every meter. The problem that I can see you're going to run into is that unless you can use more substantial joists than 90 x 45mm, you'll need around 120 supports. Using a bigger calibre of timber over the soil areas will allow it to span further with fewer supports. What is the height from the soil to the door threshold?

Please let me know if you have any questions.

Mitchell

[MrSober]

Thanks @MitchellMc 

The drop from the door brick to the concrete is about 3" or 70.5mm wouldn't fit a full sized 90x45 there with the added 19 thickness from the decking also.  The drop from the top of the alfresco concrete is 200mm at the very base, with it dropping up to 300mm at the moment a bit further out.

Was wondering if it could be almost two separate decks in the way that the alfresco is done in 90x45 and over the dirt being thicker being 140x45 or 120? Would putting a ledger board on the side of the alfresco slab help or is that something that shouldn't be done

Got a bit of dirt out there to level it in a bit better, might need to grab some more just to get it right to allow the water to flow into the 3 drains around. Then plan on covering the whole thing in plastic or matting and then cover with 20mm blue metal or something etc.

[MitchellMc]

That'll be the idea, @MrSober; the 90 x 45mm would have to go on its face for the alfresco area and then when you drop off the slab, switch to 140 x 45mm on its edge. You'll still need to have the 140mm spaced at 450mm centres, as that's the max span for decking. By using 140mm, you'll have fewer holes to dig and supports needed.

Please be aware that by creating a deck with a total height of 70mm over a concrete slab, you could see the early onset of decay as there will be next to no airflow through the structure. You should at least consider a gap between your decking boards of 5mm or larger.

A ledger board could be added to the side of the concrete slab to help create a solid transition between areas. 

Mitchell

[MrSober]

@MitchellMc,

Do you have any good resources that you have come across that makes it easier to plan out the spacing's etc when going between the different sizes? I noticed you uploaded a image of what you would expect my project to look like and wonder if you have come across some stuff that is easy to get a hold of.

Looking to draw something up soon so I can get stuck into it in my spare time, might have something done by Christmas! Maybe I have bitten off more than I can chew with the amount of things I want to get done as I got quotes of over $60k for the deck and some landscaping down the other side mostly being grass and some garden beds.

Thanks for everyone's help so far, it had me a little stuck trying to find examples of what I wanted to do as most things don't show the framing but found this site to be very helpful in that regard.

[MitchellMc]

All the spacings you're looking for are found in timber spans tables @MrSober. I've included one from our timber supplier Hyne. The "span" is how far the timber can travel in the air before it needs support. You can see that 90 x 45mm has a max span of 1600mm before it needs support, hence my recommendation of placing your support at 1000mm. I like to make conservative recommendations to be on the safe side, but you could always choose to have your supports further apart. Next down the list is 140 x 45mm, and you can now see since we've increased the calibre, it has a span of 2600mm.

No matter their size, your joists will always be spaced 450mm apart, as any further and the decking will become spongy or bouncy.

We now know the joists are spaced 450mm apart, and your supports are placed according to the chart below. That's enough info to plan most of the deck. All the ends of the joists need a perpendicular framing piece to help stop them from rolling over, and noggins are placed intermittently along and between long joists for the same reason.

Regarding the transition between the two-sized joists, it's not so hard to do. Place their top surfaces flush with each other and then the support as necessary.

Have a look at this helpful guide on How to build a deck. Sections of interest will be: How to install bearers and How to install joists.

Please let me know if you have further questions. I'm happy to walk you through it if you get stuck.

Mitchell

[MrSober]

Small update, have ordered my wood and have started this project.