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

[SMUCKY]

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!

Blake

[EricL]

Hi @SMUCKY 

Your decking frame design looks great. I'm putting my vote with design number one as it spreads out the support in a larger pattern despite using 90x45. The increased number of Tuff blocks will prevent your deck from having a springy surface. The more support your decking frame has the more stable it will be. 

My best advice is to make sure to paint the bottom of your frame with Gripset Betta 1L Waterproofing Membrane Bitumen Rubber and apply CAgroup 50mm x 20m Bearer Protector G-Tape to the top surface to extend the service life of the frame.

Let me call on our experienced members @Dave-1, @Nailbag, @TedBear, @Jewelleryrescue and @JoeAzza to see which design they'll vote for.    

If you need further assistance, please let us know.

Eric

[Dave-1]

Good Evening @SMUCKY 

Now thats a lot of effort in planning. Nice to see.

My Vote is drawing 1.

I havnt used tuff blocks so not speaking from experience for that. I do like the spans and the costings of both tho.

I do have concerns about council allowing that much of the yard to be decked. Id check sooner then later to verify.

The drainage for the area, I am not keen on French drains per say. I prefer dish drains as you can see what they are doing and dont clag up. WIth your suggestion of blue metal across the area I am not sure why? You will be removing soil in the first place I think? Id factor in some dish drains instead to a drainage pit conected to the stormwater system. 

Id love to see your project unfold As in post the finished steps throughout for a project. Please take a bunch of photos.

Dave

[Nailbag]

Hi @SMUCKY I would also go with option 1 with @EricL 

There are loads of similar projects on the workshop site to refer to, most with additional information from those who have installed them, issued and work arounds they have faced. It's worth surfing about to gather as much information as possible and learn by what others have done both well and haver not.

Nailbag

[SMUCKY]

@EricL Cheers for the feedback I figured as much for design #1 structurally wise…

Although a little confused as this design only uses 90x45 for the noggings but 140x45 for majority of the frame.

Would you recommend the paint purely on the underside of the frame or am I meant to go up the sides of each piece also? 

Thanks!

[SMUCKY]

Hi @Dave-1 appreciate the response.

The backyard currently has no existing drainage aside from one stormwater pipe in the middle sticking out of the ground (the builder did not do any landscaping). This backyard is wet all year round and in wetter/colder seasons it’s far worse, so bad it’s giving us moisture issues up against the house. My aim is to pull out minimum 100-150mm of the clay on top, run aggregate lines all around the perimeter sloping toward and into the middle where I will plumb a pit into the existing stormwater pipe. I will also install a weed matting and suffocate everything in minimum 100mm blue metal which will be my base for my tuffblocks.

Reasons being;

- to maximise how well water drains away from the deck and into the stormwater system.

- to hopefully stop any weeds/grass growing up through my deck as I won’t have access to the ground once it’s covered.

- to give me a solid base for my tuffblocks which I can move around easily to adjust to my required heights as necessary 

- I would also like one continuous solid surface that my partner and I can actually walk on (regardless if it’s been raining or not) because it still may be a while before we are a standing on an actual deck and I don’t want to be walking in a mud pit whilst I’m building it.

- I am also able to remove the clay and refill with blue metal free of charge due to family so may as well take the opportunity to do it 100% right before it’s covered by a deck for the rest of it’s life. 

I am all for any suggestions to make things better so let me know what you think! and please elaborate on ‘dish drains’ as a google search just gives me the strainer I use in my kitchen to dry my dishes 🤣

I will definitely take photos I love progress photos, I will also keep the forum updated along the way for sure.

Cheers

[SMUCKY]

Awesome thanks @Nailbag for your thoughts, I agree!

I feel I have definitely already been reading over far too much information on decks (my missus would also tell you the same 🤣). This is kind of how I have ended up with these final designs as I’ve been through a lot so far.

Just wanting to perfect it before making a start as I am a massive perfectionist!

Thanks,

Blake

[JacobZ]

Hi @SMUCKY,

Similar to the others I would say option 1 is better and as I have mentioned before, reducing the number of hangers will usually cancel out the cost of using larger materials. This becomes even clearer when you factor in that every hanger you use requires 10 x Pryda Timber Connector Screws which comes in at about $2.70 per hanger. 

To answer your questions for @EricL, you should apply bitumen paint to the underside and around a third of the sides of the joists and bearers. This will help protect the underside of the timber from moisture.

There are no issues using 90x45 as noggings because they are not there to support weight. Their primary purpose in a deck is to keep the joists straight and to prevent any twisting.

Let me know what you think.

Jacob

[SMUCKY]

@JacobZ Ahh yes I read back on our previous discussion, my apologies you certainly did mention that. I was maybe just not understanding at the time as I'm still new to all this 😂 I only made that connection once seeing these 2 different designs side by side. Sounds like I will be going with design #1 though as I figured, it is much more structurally sound and ends up coming in around the same price anyways.

Sounds good regarding the bitumen paint & the noggings thanks for that!

So im aware I use the hangers on all the joists, I assume its fine for me to use nails or screws for all the noggings. I am just wondering what is the best way to fix all the frame together around all the corners. Is there a preffered method of fixing? Do I have to install some type of 90 degree internal bracket to join everything? Or just nails/screws?

Thanks,

Blake

[JacobZ]

Hi @SMUCKY,

No need to apologise, there's a lot of information throughout the discussion so it's hard to remember everything.

As you've said, there's no need to use a hanger with your noggings. You can use ZENITH 14G - 8 x 100mm Galvanised Batten Screws through the joists into the end of the noggings. Use a Sutton Tools 5.0mm Long Series Jobber Drill Bit to put a pilot hole through your joist into your noggings before driving in your screws. As these are some fairly thick screws, this will prevent splitting in the timber.

It's worth reinforcing your corners with Dunnings 60 x 60 x 105mm M10 Galvanised Angle Brackets. Drive the same connector screws you'll use with the hangers through the holes in the bracket and into the timbers. 

Let me know if you have any further questions.

Jacob