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?

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).

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?

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

Cheers,

Tavo

Community manager's note: Check out How to build a low-level deck for expert advice.

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Comments

pepsp

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.

pepsp

@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

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/11783#Comment_11783

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

MitchellMc

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

pepsp

https://www.workshop.bunnings.com.au/discussion/comment/68328#Comment_68328

@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.

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/11791#Comment_11791

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

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/97073#Comment_97073

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

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/115175#Comment_115175

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

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/125423#Comment_125423

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.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/132318#Comment_132318

@tavo1421,

Did you ask them for the soil reactivity classification? It doesn't match with the table because I'm fairly sure it's not the information you were after. Different levels of acid sulphates in soils can affect concrete foundations, but I don't believe it has anything to do with the footer's required size.

You'll need to be quite specific with telling them what information you require. Keep in mind they might not know what the soil type is.

Unfortunately, most building codes have an attached price tag to them. If you employ the services of a professional, then they will have them on hand. If you search for the specific information you need from the codes, you'll find sites that have partially copied information from them. The tables I have provided above are an example.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/136516#Comment_136516

Hey guys,

Finally I did some progress with the excavation and prepare the terrain for start doing this.

I would like to check with you some doubts I have regarding screws and bolts:

For fixing decking board (90x19mm Merbau) to the treated pine, do you think 50mm 10G screws are ok?

In terms of the screw type, do you recommend stainless steel like this or the specific ones for treated pine like this, this or this?

For bolting the treated pine to the stirrup, which bolt size and type do you recommend?

Finally, to secure the joists to the bearers with the triple grips, I guess I should use nails, right? which type and size do you recommend?

Cheers,

Tavo

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/139420#Comment_139420

I'm glad to hear you've started on your project @tavo1421.

It would be my opinion that the Zenith 10G x 50mm Stainless Steel Type 17 Countersunk Rib Head Decking Screws - 500 Pack would be the best option for your project. Not only do they have fantastic corrosion resistance, but they look amazing too. 50mm x 10G screws are a suitable calibre for fixing your decking boards.

Have you decided on what dimensions the treated pine being bolted into the stirrup will be? You'll need a bolt of approximately 8mm thickness that is long enough to pass through both the timber and the stirrup. So, if you were going to use a Pryda Post Anchor Half Stirrup Solid Stem 300mm M10 carrying Treated Pine Outdoor Timber Framing 140 x 45mm, you'd need a Zenith M8 x 60mm Hot Dipped Galvanised Cup Head Bolt And Nut.

Pryda does their own 35 x 3.15mm Timber Connector Nails for fixing all their bracing and timber connectors. You might find the Pryda Joist Hanger Suits 45 x 90mm a better option for connecting the joists to bearers than triple grips.

Please let me know if you need further assistance or have questions.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/141352#Comment_141352

Hey Mitchell,

I will use 90x45mm for both bearers and joists in a single layer. So, I guess the bolts are the same, right?

Thanks for all the info!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/142807#Comment_142807

That would be correct, @tavo1421. The 45mm thickness is the same, and a 60mm bolt would be sufficient.

Please keep us updated and remember to take lots of pictures of your progress.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/143830#Comment_143830

Awesome, thanks again.

Regarding the joist hungers. The bearers are centered to the footer, so there is a gap between them and the wall. In order to secure the decking boards which will be close to the wall I would need to somehow extend the decking structure. My idea is to add some small joists to the external side of the bearers (see pic). I wonder if that's the way it is usually done? or it's needed a halved joint between the joists and the bearers? There are 33 joists and 2 bearers in my deck so not too happy to do 66 halved joints 🙂 so maybe the "small joists" could be a (lazy) alternative. If that's the case, do you recommend to use joist hungers again to secure them to the bearer or I could just use two/three timber screws from the other side of the bearer?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/144622#Comment_144622

Hi @tavo1421,

If it is a brick wall, you could consider bolting the bearer directly onto the wall instead of being supported by posts. This is done when footers can't be placed close enough to the wall. The bearer is then called a ledger, and the wall supports the deck. Below I've illustrated a hybrid method, where you still keep the posts and bolt a secondary ledger to the wall bridging the gap. However, you can leave out the posts completely.

Although your method would most likely work, having one end of the joist unsupported like that isn't recommended.

Please let me know if you have questions.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/145201#Comment_145201

Thanks for your response.

Yeah, I was trying to avoid to drill the wall and bolt the ledger to the house, but it would make everything easier, less footers and it will probably be more robust.

As it's the house foundation, it's actually concrete, see pics below.

I would need to know how to do it properly because don't want to cause any damage to the foundation. I would appreciate any guidance or advice on this.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/145658#Comment_145658

You'd drill into the concrete foundation with a masonry drillbit @tavo1421, and I can't see any way you could damage the foundation. A Dynabolt can then be used to fix the ledger board to the foundation.

If you need to go through the tiles, that might be a bit different. Cranking down on the Dynabolts could crack the tiles. It's just an option that I thought you should know about. Will those tiles on the side of the foundation be visible after the deck has been constructed? If not, you might consider removing them.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/146009#Comment_146009

Thanks @MitchellMc for your response.

Well, the deck has to be flash with the top of that step/tiles, so the ledger should be 19mm (decking board width) below that line. That means that the bolts will need to go through those tiles in that part of the wall. There are other parts of the wall where there is brick at that height and concrete below. You can see that in the picture I posted in the first message of this thread.

Any idea of how many bolts, size and distance between the bolts? 90x45 for those ledgers should still be ok?

Those dynabolts are the ones you hammer through the hole and they expand, then you use a nut to fix it to the ledger, right?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/146299#Comment_146299

Hi @tavo1421,

90 x 45 outdoor framing timber would be suitable for the ledger, and I'd suggest placing Ramset 12 x 125mm Galvanised DynaBolts every 600-800mm along its length. Once you've placed your Dynabolts through the timber, you can place a stack of five galvanised washers onto the bolts before inserting them into the wall. I'll illustrate this below, and the washers are in red. This gap stops moisture from being caught between the ledger and tiles and prevents premature decay.

Dynabolts get inserted into a hole, and the action of turning the nut expands them.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/146539#Comment_146539

Amazing thanks for the explanation.

I wonder if, on the other side of the deck, where there is not a brick wall but a colorbond fence, I could extend the joists as I explained before? Is there another better way to get closer to the fence?

Thanks again.

MitchellMc

You can certainly extend those joists as they can be counter-levered out a certain distance. Since the space is 1300mm wide, then I'd set the posts at around the 1000mm mark and have an overhang of 30cm past the post.

Here's another picture to illustrate.

Mitchell

tavo1421

https://www.workshop.bunnings.com.au/discussion/comment/12460#Comment_12460

Thanks again.

Sorry but as I move forward with the design I have new doubts.

In the side closer to the colorbond, in the joint between two bearers like here:

Which sort of connector should I use? A connector plate like this, Knuckle Nailplate like this or what you recommend?

For the joint bridges like the ones below, should I use a 90 degree connector with nails? Can I use some type of timber screw from the other side? both? which plates and/or screws do you recommend?

Same for the corners like the one below. Should I use a 90 degree connector and nails from inside? Can I use some type of timber screw from external side? both? which plates and/or screws do you recommend?

Cheers,

Tavo

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/68751#Comment_68751

Either of those two connector plates would be sufficient @tavo1421. Personally, I'd recommend going with the Pryda Nail-On Connector Plate 75 x 125mm so you can drive some decent length nails into the timber.

For the joint bridges, Pryda Joist Hangers Suits 45 x 90mm would be the best choice. Alternatively, you could screw through the timber into their ends.

At the corners, I'd recommend screwing through them with two Zenith 14G x 85mm Galvanised Type 17 Batten Bugle Head Timber Screws. Alternatively, you could use a Pryda Multigrip 100 x 35mm on the inside and outside of the joint.

I hope that answers your questions. Please let me know if there is anything else.

Mitchell

Jason

How is your deck project going @tavo1421?

It would be fantastic to get an update as your project has been very popular with the community.

Many thanks,

Jason

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