Low-level composite deck over concrete and soil

[oninpena]

This low-level deck using Ekodeck composite boards covered a concrete area and required pavers to support pedestal feet on an unconcreted section.

• The project
• How to build a low-level deck
• More inspiration for your decking project

The project

I decided to put a low-level composite deck on my alfresco area. Part of it would be on concrete and part of it would be on the soil at the side of the house.

The build was quite a task, and I appreciate the help and advice that EricL and MitchellMc gave me over the course of the project. 

I was concerned about the pipe drain circled in red, but Eric said it was OK to build over it. He suggested building a removable panel in the deck for access to the drain if required.

I used floorplanner to sketch up a plan of the area and a plan for a possible decking layout.

I then did a more detailed design. I needed to go with double breaker boards to reduce wastage and cover the length of decking that I wanted.

Eric supplied advice on how to fix the angle brackets to the concrete and the timber frame (DynaBolts on the concrete and galvanised hex head bolts and nuts with galvanised washers for the timber, along with Pryda timber connector nails for the Pryda joist hangers).

Mitchell helped me fine-tune the placement of supports for the frame.

The next problem was how to fix fascia boards around the edges of the deck.

Where the pedestals were at the very edge of the deck it looked as though I might have to cut the boards to fit, unless I could use a spacer where the red box is. Mitchell advised me to screw two lengths of timber together and place them on the pedestals. 

Finally I completed the frame after weeks of collecting materials and tools, measuring, digging and tamping for the pavers, cutting, drilling, screwing and going back and forth to Bunnings to get more materials.

 

 

I could finally begin laying the boards.

 

The one thing I was not prepared for was the size of the slope on the alfresco concrete. I didn't think there would be that much fall, so I had to switch to bigger angle brackets at one point and also used a lot more pedestal foot than I had anticipated.

At the end there were still some minor things left to fix up, but for a first-time D.I.Y. project I'm pretty happy with how it turned out.

 

 

 

 

 

How to build a low-level deck

A low-level deck can pose a range of potential design and installation problems, with challenges around ventilation, drainage, termites and rot. But it doesn't have to be a difficult project once you take the time to understand the basics of how a low-level deck is put together.

Experienced Bunnings Workshop member Adam Woodhams has created a comprehensive guide to building your own low-level deck, which provides an excellent reference for getting started. 

Resident D.I.Y. expert MitchellMc has also put together a step-by-step guide and video tutorial showing how to build a floating deck using adjustable pedestal feet.

More inspiration for your decking project

Bunnings Workshop member Nat2 used Ekodeck composite decking boards provide a clean, handsome finish to this low-level deck built around a bay window.

Workshop member Backyardtradie used Merbau decking boards to transform their outdoor entertaining area with this solid low-level deck.

Whether you're building a new deck or rejuvenating an existing one, you can get inspired by the clever and creative Bunnings Workshop community in our collection of Top 10 most popular deck projects and inspiring low-level deck builds.

Let us know if you need a hand with your deck project – we're here to help.

[Dave-1]

@oninpena 

That deck looks pretty sweet! I liked how you explained your working out and then found gold amongst the photos when you pointed out the slope was steeper then you had imagined. These are the things that catch us unaware first time for sure. Thank you for the explanation!

Dave

[oninpena]

thanks @Dave-1 and you are welcome, glad I could help!

[Bluetooth]

@oninpena  What a terrific looking deck! You have inspired me to think about tackling a deck in my back garden. I'll take some photos and come back for advice from the team. I'll definitely be bookmarking your build.

Why did you decide to go with composite over wood? What were your considerations?

[MitchellMc]

We'll be looking forward to following your project @Bluetooth. Let us know when you have questions.

Mitchell

[oninpena]

Thanks,@Bluetooth !  Three things that I really like about composite are the ease of installation, less maintenance, and durability. The drawback is the cost.

[Graham3196]

I want to use 140mm wide boards on the deck surface.       have read that wide boards should be attached by one central screw so the board can expand and contract without splitting.      In some cases the timber is sealed on all surfaces to minimise the change in dimensions with humidity so they dont split or cup.

What do you recommend.   Should I seal the boards before attaching them?

Cheers

Graham

[EricL]

Hello @Graham3196

Welcome to the Bunnings Workshop community. It's magnificent to have you join us, and thank you for sharing your question about your decking boards.

Sealing the decking board before installing them is a great way of protecting it from heat and moisture. Since timber decking is a natural product it will expand and contract depending on the temperature. Minimizing the entry of moisture into the panel will reduce the chances of it twisting and buckling. 

I suggest a minimum gap of 6mm when using 140x19 decking boards. It's also important to consider the distance of the decking frame from the ground. If there is not enough ventilation, cupping may occur on the panels, it's vital that there is enough ventilation under the deck. I recommend drilling pilot holes 15mm from the edge of the panel to prevent splitting when the panel moves.

If you have any other questions we can help with, please let us know.

Eric

[kjm]

I am looking at building a similar deck but my clearance is too low. At the worst point I will only have 45cm from the tile to the top of the deck. I am thinking of using thin joist with plastic spacers to keep it raised from the tiles. Would using merbau decking board an issue , with such low clearance ? Another option for me is to remove the tiles which might give me a little bit more clearance.

Secondly what to do in areas where there are termite barriers ?  The deck would be slightly higher than barrier and currently my plans is to leave a 25cm gap but I am worried it will look ugly. As you can see from the below pictures the barrier seems to end where the sliding door starts (or i could be wrong and there is some under the tiles as well but not sure.

Termite barrier

[MitchellMc]

Welcome to the Bunnings Workshop community @kjm. It's wonderful to have you join us, and many thanks for your question about creating a low-level deck.

55mm is an exceptionally small amount of space to build a deck within. Once you remove the decking board thickness of 19mm, that leaves you with 36mm for your timber joists. Even if you place a 90 x 35mm H3-treated Pine timber on its face, it would still be sitting directly on the tiles. Perhaps you could squeeze a 1mm plastic packer underneath it. For the section that has a 45mm gap, there's no solution I can think of that would involve a timber frame under your decking; there's just not enough room.

Is that a termite barrier or a dampcourse layer? In either case, the timber decking shouldn't go above that level if it's hard against the wall. You'd need to speak with your local building authority regarding the proximity of your deck to the termite barrier. If you have issues with termites in your area, perhaps you might like to consider termite-resistant Ekodeck instead of timber decking.

It's worth pointing out that with such a minimal amount of room and the timber being close to the tiles, any water entering this area will find it hard to escape. This trapped moisture will cause the early onset of decay, and you should expect a shortened life of the deck. 

If you haven't already had a read through I'd suggest taking a look at this helpful guide: How to build a low-level deck.

Please let me know if you have any questions.

Mitchell

[ChanceChippy]

@oninpena 

The deck looks great and has given me a good idea of how to approach a low-level deck build for the old townhouse we bought recently.

However doing some research online, I noticed a few articles not advising low-level decks over slabs or brick patios as the drainage could be an issue. What ar your thoughts on this and did you take this into account? or were you happy with your slab's fall and runoff into the rocked area?

[Jason]

Welcome to the Bunnings Workshop community @ChanceChippy. We're pleased to have you join us and look forward to seeing how you can put your stamp on your townhouse. Congrats on the new purchase.

As noted above, experienced Bunnings Workshop member @Adam_W has created a comprehensive guide to building your own low-level deck, which provides an excellent reference for getting started. He notes that there are three main concerns with low level decks that might lead to your deck having a reduced lifespan:

1. Ventilation – Good air movement is required beneath a deck to prevent moisture from building up and damaging the deck sub-structure and fixtures.

2. Drainage – Surface water needs to flow naturally away to prevent rot and timber movement from swelling. If bearers are too low they may restrict water movement and over time soil will build-up, further hindering water movement. If there is too much moisture and inadequate ventilation decking boards can cup and bow, too.

3. Termites and rotting – If materials are too close to the ground or you cannot easily access them, then the likelihood of attack from termites or the development of wood-rotting fungus is more likely.

Have a look at the guide and then we would encourage you to hit the Ask a question button and share more details of your project so our experts can assist.

All the best,

Jason

[EricL]

Hi @ChanceChippy 

It's great that @oninpena's low-level decking project has inspired you to plan your own low-level deck. One of the most critical parts of a low-level deck is drainage and ventilation. It's often one of the first parts of a decking plan that we discuss with our members. 

For example, if you are building a low-level deck and the space available to you is 200mm you can make a quick calculation on how much space you'll have left under the deck. If you were using 90 x 45 for your framing and a standard decking panel of 90 x 19 these would occupy a space of 109mm. When this amount is taken away from your 200mm this leaves you with a gap of 91mm. 

Now if your slab has a fall, then this gap will get bigger as your decking frame goes farther. In an ideal situation you would want a larger gap, but this is what's available to you. This is something that you'll need to consider when you start planning your decking frame.

In regards to building over soil, we always recommend that you create a slope or fall so that water washes aways from the bottom of your deck. We also suggest putting in weedmat and gravel to facilitate drainage. Some members have even gone as far as putting in drain coil for extensive drainage - Low single layer deck build by @melbs.

I suggest drawing up your framing plans and sharing it with the community. 

If you have any questions about your plans, don't hesitate to post them. We're here to help.

Eric

[ScottR]

This is a good inspiration for my decking project! Thanks for making this!

Curious though, how did you secure the frame of the deck? In the photo below that I got from your image, you used angle brackets-- but did you put the frame side to side with the brick or was there a gap? Thank you! 

I'm planning to make my deck free standing/floating and not use any angle brackets but pedestal feet throughout but I have brick house for the corner of the frames. 

[EricL]

Hello @ScottR 

Let me tag @oninpena to make them aware of your question. If I recall correctly a very small gap was placed between the brick and the timber frame. 

Eric

[oninpena]

Hi @ScottR ,

Yes, from memory I believe there is a 25mm gap between the bricks and the frame, and 3mm gap between the bricks and decking board.

The frame was only secured to the concrete floor with dynabolts.

Hope this helps!

[ScottR]

Thanks! Definitely helped! I forgot to ask what was your fall directly from alfresco to concrete at the nearest window? Mine seems to be around ~170mm. 

Also, what size of angle brackets did you use?  Thanks!

[EricL]

Hello @ScottR 

Let me tag @oninpena to make them aware of your question. For your assembly I would suggest using Dunnings 65 x 130 x 65 x 5mm M12 Galvanised Angle Bracket. I can't recall if they used a larger bracket, but I do know that they used adjustable pedestals in the higher sections of the decking frame. 

If you have any other questions we can help with, please let us know.

Eric

[yeahboo]

@oninpena , sorry, this maybe a few years late... but I'm quite new to building and wanted to know how you took into account the "adjustments"that may happen with the angle brackets? the bolt isn't a perfect fit in the hole of the angle bracket right? so how did you take into account that when you fastened the angle bracket for the joist?

Also, when you built the frame, did you build the outer first and fastened the angle brackets straight away? Thanks!

[lanaisgood]

wow!! looks amazing!! well done.

[MitchellMc]

Welcome to the Bunnings Workshop community @lanaisgood. It's sensational to have you join us and it's amazing to see you've enjoyed this project.

Do you have your own decking project in the works? If so, you might like to check out our Top 10 most popular deck projects for inspiration. Also, the guide on How to build a low-level deck is a great place to start your planning, as it has heaps of relevant information.

We look forward to hearing all about your projects and plans around the house and garden. Please feel free to reach out anytime you need assistance or have something to share with the community.

Mitchell
 

[oninpena]

hey @yeahboo , sorry for the late reply. For the brackets and bolts, I just went into the store and test fit the bolts into the bracket holes. I used galvanized bolts/nuts and washers.