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How to build low-lying deck over concrete and lawn?

SMUCKY
Just Starting Out

How to build low-lying deck over concrete and lawn?

Hi all - new here & hoping to maybe have some questions answered regarding some upcoming work im planning at my place!

We have a small backyard that is half concrete/half grass, we are wanting to make the 47m2 space more useable so am planning on decking over the whole thing essentially with a roof covering over the top one day too. Due to poor drainage in the existing grass area I will be starting off by making the drainage sufficient, concreting in the posts, & then covering essentially the whole backyard in blue metal then build the deck over the top. Due to the small height I have (70mm) ontop of the slab I will be using ClickDeck's extra low profile system to make the job possible. Then due to the small clearance in the grass area I have, the deck will be a single-level deck design & I will be leaving the finished height of the ground below much lower than it is currently as to avoid moisture issues under the deck.

My question is, judging by my rough plans I drew up. Am I in the right direction? Do I have too much framing as it does seems like a lot. Although I have based most of my measurements off of others advice but wondering if its overkill.

Essentially plan on concreting in posts, notching out posts to sit joists on & running a joist only system with hangers in place due to my overall clearance.

I'm aware of council requirements on decks & will have to alter the design to suit.

I'll include photo of what the backyard looks like now as well as my plans.

 

Thanks in advance!

 

BlakeDeck-revision2.jpgIMG_0323.JPGclickdeck.jpgIMG_0232.JPG

MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: How to build low-lying deck over concrete and lawn?

Welcome to the Bunnings Workshop community @SMUCKY. It's wonderful to have you join us, and many thanks for your question about building a deck.

Your plan looks solid, and it's clear you've put a lot of thought into it. The spans you’ve chosen are within the recommended limits, which is exactly what I would suggest. While it’s possible to push the spans further, this can result in a deck that feels a bit bouncy underfoot, so what you have now should provide a sturdy and stable finish.

 

Addressing the drainage issues and concreting in the posts sounds like a smart approach, especially with the low clearance and potential moisture concerns. By creating the single-level deck with ample ventilation underneath, you’ll reduce the risk of moisture build-up, which is key for the deck's longevity.

 

Overall, your layout looks good for the space and conditions you've described. However, remember to approach the council, as if a permit is required, you might also need to employ the services of a draftsperson to create plans for submission. Ultimately, they'll decide if your approach is appropriate.

Please let me know if you have any questions.

Mitchell
 

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Re: How to build low-lying deck over concrete and lawn?

deck-revision2.jpeg

Hey thanks for the good info @MitchellMc!

 

I am thinking about having the edge of the deck along the footpath come down and over and have a fascia board the whole way along. Or potentially even have a step depending once I figure out the height of the existing concrete as it might be a large drop off. My concern though is getting my posts as close to the edge as possible it probably won’t be close enough so my fascia board hangs over the footpath. To do this would I have to double up (or triple) on my bearer closest to the footpath so to give me more overhang from the last post?

And is it easy enough to incorporate steps in? I was thinking having a step in from the edge. Are there any guides on here with maybe something similar? 
I have highlighted in orange roughly where my fascia board would overhang and in purple roughly where the step would go.

 

What do you think?

Cheers

MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: How to build low-lying deck over concrete and lawn?

Hi @SMUCKY,

 

For the overhang, dropping the bearer down below the joists and running them across the top of the bearer to your desired overhang would work. This will create a cantilevered effect that gives you the extra overhang without needing to double or triple up on the bearer. By having the bearer below the joists, you can still ensure structural integrity while allowing the fascia board to extend over the edge.

 

As for incorporating steps, they can be a little tricky, but nothing too complicated for an experienced D.I.Y.er. The height of the deck and the drop from the existing concrete will determine the size and design of the steps. If you can provide those measurements, I’d be happy to assist you in creating a design for the frame of the steps. Typically, you’ll want the steps to be comfortable to use, with each step’s rise being no more than 190mm, and the tread depth should be around 250mm or so for stability. While I don’t know of any guides specific to step construction for decks on the site, building the frame for steps is very similar to constructing a deck frame—just on a smaller scale and at the appropriate height.

 

Mitchell

 

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Re: How to build low-lying deck over concrete and lawn?

@MitchellMc That makes sense thank you for the tip. So with this kind of setup I have how much overhang roughly can I have the joist overhanging the bearer safely? Also if I have the joists sitting on top of the bearer how do I fix them down then? I assume I will need some sort of strap fixing them together?
Then I assume with the ClickDeck I can essentially do something similar as they allow for a 200mm cantilevar with my setup.

That would be really appreciated with the steps. This weekend I will speak with the partner and work out more what we’re after and I’ll get back to you next week with some measurements and more info.

Thanks Mitchell

SMUCKY
Just Starting Out

Re: How to build low-lying deck over concrete and lawn?

Also @MitchellMc sorry, I was meant to also ask regarding the posts and their footings.

 

Is there any way to reduce with my existing design the amount of posts? I’m just worried about trying to manage running agg lines all throughout the backyard with this many posts I have to concrete in. I just may not have the room I’m after.

 

And typically what kind of size hole would you deem fit for purpose for the posts? 300x300x300? And how much concrete is recommended to fill each hole? I was measuring up with a concrete calculator last night and that many posts with that hole size is roughly 77 20kg bags!!! (0.7m3)

 

Blake

MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: How to build low-lying deck over concrete and lawn?

Hi Blake (@SMUCKY),

 

You could potentially space the posts slightly wider, but I’d recommend referring to a span table to determine the maximum allowable span for the bearers you’re using. The 1200mm spacing you have now is generally what I'd recommend for solid support, but adjusting it could work if it meets the span requirements.

 

For the footings, determining the exact size is best left to an engineer who can assess the soil type in your area. Typically, a 300 x 300mm hole that’s 450mm deep would be sufficient, and you’d likely need around one and a half bags of concrete per hole. If you're looking to reduce the concrete volume slightly, a 300 x 300 x 300mm hole might work, but that would depend on both soil conditions and the load the posts need to bear. 

 

Mitchell

 

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