How to build low level deck over concrete and grass?

[rwa1994]

Hi all,

I am planning to build my own deck out the back of my new house. I have some plans and some questions with the plans. 

My questions are:

1. What spacing do I need for my bearers, joists and stumps?

2. I only have 130mm clearance between concrete slab and doorway entrance. I am going to create a single layered structure that I saw on someone else’s post but am I able to use metal stirrups like this one and just dynabolt it to the ground and put the wood straight on the concrete?

3. Am I able to use 90x45 H4 treated pine for my structure? I can't use 140mm as it won't fit clearance.

Thank you!

 

[Nailbag]

Hi @rwa1994 no need for any apologies at all. We are all just trying to understand what you're trying to achieve. It's a big project so there will always be lots of questions from both sides. 😁

Since you're not using joists on bearers the thicker the joist timber the longer the span over the stumps. If you were to use 90mm x 45mm H3 F7 treated pine can span a maximum of 1200mm centre-to-centre on footings as a continuous joist. Increase As you increase joist height and the span increases, but you need to consider your finish level of the decking boards to the sliding doors. 

For extra strength and to prevent the joists from twisting, I would install noggins every 800-900mm

The joists could be fixed to the timber stumps with Pryda Unitie's 

I'll tag in @MitchellMc as he's been involved with quite a few discussions in the community as well as built a low level deck himself. So, can steer you to relevant articles.

Regards, Nailbag

[MitchellMc]

Hi @rwa1994,

From your plan, it appears that you have designed it for a two-level joist over bearer deck. Was that your intention? You have stumps shown, red bearers and blue joists.

On Jacob's design, it's a single-level deck. Over the concrete area, brackets are used to attach the joists. Over the grass, you'll use stumps. For the area over the soil, your joist must be supported around every 1200mm. If you didn't want to dig holes and concrete in stumps you could use pavers and pedestal feet.

Please let me know if you have any questions.

Mitchell

[Dave-1]

Morning @rwa1994 

No appologies needed or expected. All of us has had the first project stress, second and even third project stresses

I had presumed you were going off that render/sketch up and was counting the points of contact with the ground.

Its easy for us to sit and tell you what we have done/what is right verse what you are doing. The safest way is for you to be sure of things yourself and niot just take say "my word" that it is ok.

So a good starting point is -

-The length and breadth of the area you are working with (You have that)

-How far apart are the joists that will support your deck will be (450-600mm tho 450mm is the better)

-Supports for the joists as you are buiilding a low level deck (right angle brackets over concrete) posts of some kind into the ground with soil removed so its not touching the timber and to provide air flow.

-Posts into the ground, You can use stirrups, timber or the adjustable black thingies that you will need a hard surface to sit them on.

-

I find sketching it myself to be the best way of nutting out how something is built, often I start from the top and work my way back and it shows to what is needed for each step.

For instance, 5,600 by 4,700 area I can draw that easily, then I start thinking that there is a pillar in the way and its going to be over grass and concrete but can only be so high as I dont want it higher then the door to the house. (This gives you a height over concrete to start with)

-So now we have the picture and dimension of the deck we drew ourselves (please draw it ) it really helps you.

-How do we support this whole area? We know the rule is 450mm between joists (I just googled "Spacing between deck joists Australia")

-So now we divide the distance of the deck by the joists, (At this point you may want two sketches. The joists will detetermin which way the floorboards will lay. Depends on what you want. The sketchup render means that they will run from left to right. if you do the joists the other way then the boards will run up and down. Once you have drawn the deck/yard you will go  "ahhh lightbulb, I like this way more!

-Now we have sorted the joists, how are we going to support them and how often do we need to? This is the part where I like stirrups, @Nailbag, @JacobZ  likes posts I think?, So it comes down to your preference and how competant you feel for that. Spacing tends to be 1500mm to 1800mm apart tho I suggest closer to the 1500mm as less chance of flex in your deck.

- Draw the frame up, include your measurements You will see a pattern form especially for the posts.

-Concrete the footings/posts in. I went through two bags of concrete per post for my deck (have a look when you are sketching and you will see how it rose up) Now you dont need super deep posts. Maybe 20-30cm deep? As your deck isnt supporting anything higher.

So you should have a few sketches now, I find if I sketch each on a new page I can flip between them for perspective, kind of like layers of a cake.

There are various ways to set your posts/stirrups in concrete.

I supported a line of posts in the air then poured concrete in the holes.

I have seen the framework built first that the posts attach to (frame issupported by bricks) and then posts attached. concrete poured.

There are a few other ways I have seen. 

Never worry about asking questions We all ask questions and I still ask questions myself for jobs I dont know about. 

Dave

[rwa1994]

Hey @Dave-1 , @MitchellMc  and @Nailbag ,

Thanks so much for all the advice. I have been MIA working on my sketches. I have attached what I think will work in the space. I just want to double check that I have enough support with the joists or haven't over engineered anything. 

You're right, once I sketched it out I got a way clearer picture in my head. 

Thanks guys

[Dave-1]

Evening @rwa1994 

Much nicer and all of a sudden I am breathing easier Love that knowledge is confidance feeling! 

Id be happy with that

Dave

[rwa1994]

Hey @Dave-1 ,

Thanks heaps. The concrete holes for the stirrups/posts are in an okay distance from eachother to support the deck so that it won't flex? 

Thank you mate

[Dave-1]

Evening @rwa1994 

Id say yes, and nice way to do it as well. I wouldnt have thought of that stagger and would have done a straight line Learn something new every day!

Dave

[MitchellMc]

That's looking pretty good @rwa1994!

Mitchell