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Ground level low-profile deck

tavo1421
Budding Contributor

Ground level low-profile deck

Hi everyone,

 

I want to build a deck of around 14m x 1.3m on one of the sides of my house.
I checked many forums, websites and post here and there. I learned a lot but I still have a lot of doubts. Most of the information out there is about huge decks built in which I guess are cyclonic areas or with extreme weather conditions like snow, etc. I live in NSW and I think a ground-level deck could be somehow much and simpler, with fewer components while remaining robust and compliant with the local standards.

As you can see in the pictures below, the area is next to the neighbor lot. Also, I need to dig out some centimeters (maybe around 20'ish cm) in order to make the deck flush with the terrace and side entrance. Currently, there are 4cm between the terrace level and the soil.

  • Do I need to leave a gap between the colorbond fence and the deck?

decking-area.png 

From my understanding, the classic deck structure has concrete pads, some sort of galvanised stirrup like this, posts, beams, joists and the decking board. In order to make it flush with the terrace, If I use all the above, I will need to remove a lot of dirt . 

For instance, I was thinking of using like a 300mx300m concrete pad, galvanised stirrup on top of it and then beams and joists at the same level like the following (sorry for my draft 2d/3d sketch). 

draft.jpg

What would be the minimum required components for a low-profile deck? Which brackets are appropriate for a low-profile deck without posts?

 

Providing that I need to remove some dirt next to the fence sleepers (see img below) they used to level up the fence:

  • I wonder if it could somehow collapse. What can I do to prevent that? 

sliding-door.png

 

Last but not least, can someone (@MitchellMc ? :laugh: ) help me to calculate the beams/joist and concrete pad needed based on the above deck dimensions?

 

Cheers,

Tavo

pepsp
Established Contributor

Re: Ground level low-profile deck

Hi @tavo1421  sounds like a great project you’re planning. A couple of thoughts to get you started:

- there are some helpful threads on this forum like https://www.workshop.bunnings.com.au/t5/How-To/How-to-build-a-low-level-deck/ba-p/45715  by @Adam_W 
- I found this how to guide helpful for identifying bearer and joist sizes for my deck

- you may want to consider a modular decking system  which seems pretty quick and easy to put together- all parts are available from Bunnings

- I would avoid digging a long excavation right on the boundary. You would have to retain it and that would need approval as it’s right on the edge of the lot and could affect your neighbour’s land.. Could your deck be 200nm off the existing ground level? The Good Times modular deck mentioned above is designed for that situation.

- being so close to the boundary you should talk to your local Council about whether you need approval. In NSW decks of no more than 25m2 are permitted without an approval under the  Codes SEPP as long as they’re more than 900mm from the lot boundary and behind the building line from the road frontage.

 

My low level deck was a bit bigger than yours and was a bit of work (took a month of weekends in November including rain delay) but was totally worth it. Good luck and keep us posted on your progress.

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pepsp
Established Contributor

Re: Ground level low-profile deck

@tavo1421 here’s a couple of photos of the substructure of my deck in case it’s helpful. Bearers 140 x 45 H3 treated pine, 300mm half stirrups for stumps, concreted in the ground over the part that wasn’t concrete. I used a plastic adjustable support over the concrete.

 

finished level is 250mm above ground height to be level with the existing floor 

 

BFC249F0-C092-445E-AED7-DB0CAC7D81BB.jpeg

08A9551C-F24C-4595-B3D2-6C09F0EFFF47.jpeg

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tavo1421
Budding Contributor

Re: Ground level low-profile deck

Thanks @pepsp for taking the time to respond, I appreciate it!

 

Yours looks quite similar to what I need to do. I apologize in advance but I need to ask you some more questions.

 

It seems you used 90x45 for the joists, right? 

In the area that wasn’t concrete, those 250mm you mentioned are between the bottom of the bearers and the ground? That gap is my concern, the area I need to cover is sometimes a bit muddy also I read that it's ok a minimum of 75mm for termite protection and ventilation. Even though that wood won't be in contact with the soil and there will be a weedmat between them I wonder if, just in case, I should use H4 or H5 bearers and joists?

 

In terms of the concrete pad, how deep have you dug the hole?

 

For the stirrup, you used something like this, right? Have you bolted to the concrete or set into it?

 

Cheers,

Tavo

 

 

 

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Ground level low-profile deck

Welcome to the Bunnings Workshop community @tavo1421. It's amazing to have you join us and many thanks for your questions.

 

It's great to see you've been receiving some fantastic assistance from @pepsp.

 

I've included a rough plan of how your deck could be constructed. You must check with your local council regarding requirements on building a timber structure that close to a boundary fence. The fence posts are held up by concrete footers and when excavating around those you should take care. Any idea how far you need to dig down? My plan utilises 90 x 45mm H3 timber.

 

You'll need to investigate what options are available for structural grade H4 timber as it is not readily available. Therefore decks are generally built a certain height above the soil. In @Adam_W's article, he references ways to minimise damage from the soil in close proximity to your timbers.

 

I look forward to following along with your build and please feel free to ask as many questions as you like. We're here to help.

 

Mitchell

 

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pepsp
Established Contributor

Re: Ground level low-profile deck

@tavo1421  The 250mm is finished height to the top of the decking boards, so the 140mm bearers are about 90mm off the soil. 

Yes the stirrups you linked to are the ones I used. I dug down far enough so I had around 150mm below the base of the stirrups, added gravel at the bottom (about 50mm thick) for drainage and compaction then filled the hole with concrete. The square holes were about two shovel widths wide. Used around two to three bags of premix per hole and I had the stirrups suspended from the beams (which were already levelled) down into the holes. One thing to watch out for is double checking you don’t push the stirrups out of level when you’re putting the concrete in. Easy enough to correct when it’s wet. When it’s dry, not  so much!

 

For your situation definitely look at the dimensions @MitchellMc has provided- smaller bearers are fine you just need to have more supports. I don’t particularly enjoy digging holes and I had enough clearance for 140mm bearers so that’s the way I went.


Also have a look at this builders edge product: https://www.bunnings.com.au/builders-edge-pedestal-foot-smallfoot-35-60mm_p2450074 


I used the bigger version for the concrete section of my deck, but I actually think you could get away with a paver in well compacted soil with this on top. Anyway, I spent a few dollars on a couple of footing options to play around with before I committed to the whole thing. It just helped me understand what the options were.

 

Re H3 vs H4, you could use H3 then paint with something like diggers eco protecta for added protection.

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tavo1421
Budding Contributor

Re: Ground level low-profile deck

Thanks @MitchellMc for your response.

I see, it's not easy to get H4 lumber.

Oh 90x45 bearers and joists will save me some digging. Or you meant just for the joists?

I'm still unsure how to calculate the Footing Diameter and depth. Could you help me with that?

 

Also, I saw some people use cardboard tubes to pour the concrete but cannot find that product on the Bunnings website. Are them really needed or I can pour the concrete directly in the the hole? 

 

Cheers

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tavo1421
Budding Contributor

Re: Ground level low-profile deck

Thanks @pepsp , you provided me very useful information. Those pedestal are awesome but I think I will go for the stirrups hot dipped in concrete.

I definitely will use that paint you recommended. 

 

Cheers

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Ground level low-profile deck

You could use 90 x 45mm for the entire frame, including joists and bearers @tavo1421.

 

Determining a footer size is not as simple as just digging a hole and filling it with concrete. A geotechnical engineer needs to take soil samples from the site, subject them to varying tests, and then specify the correct site classification according to Australian Standard AS 2870/2011 - Residential slabs and footings. They will then determine the footer sized required for the build. This process is generally required if you are submitting plans to council for approval.

 

You could attempt to establish the required size yourself by contacting the council and seeing if they can provide the soil type information in your area. You'd then need to download a copy of Australian Standard AS 2870/2011 to get sizing.

 

A footer of 350 x 350 x 450mm would be the minimum sized footer for stable sites. You'll find the more reactive the soil type, the larger the footer needs to be. If in doubt, I'd encourage you to employ the services of a qualified professional.

 

The cardboard tubes are not needed to create an inground footer, and the concrete can be poured directly in the hole. Those tubes are usually used to create circular piers which extend above ground.

 

Mitchell

 

Deck footing size.png

 

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tavo1421
Budding Contributor

Re: Ground level low-profile deck

Thanks @MitchellMc .

 

I asked the council and they said we have Class 5 soil, which for some reason doesn't match with your table. It seems it's a different classification, just for Acid Sulfate Soils. As per the council site it means:

"Class 5: Acid sulfate soils are not typically found in Class 5 areas. Areas classified as Class 5 are located within 500 metres on adjacent class 1,2,3 or 4 land."

 

I also tried to get that standard but for my surprise it's $300. 

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