How to build a low-level deck for alfresco area?

Hi,

We are planning to build a Merbau deck with picture frame edge on the concrete Alfresco in our new house. There's a concrete of 1000m width around the alfresco area.The height of the brick below the Alfresco Stacker door is 13cm, so we reckon the height of the deck should be 13cmm once its built. We are thinking to extend the deck over that concrete area (as shown below) as well so that it ends next to the lawn when we plan to put that later and also we have some space to the sides. Does it sound like a good plan? Would really appreciate if you could help us with the materials required and a plan as to where to place the joists and bearers with the below dimensions ?

There's a silt pit in the corner (concrete area). Is it ok to extend the deck over it ?

Screen Shot 2022-12-28 at 12.05.53 pm.png Alfresco concrete

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Comments

KatieC

Hi @sanjurajan,

Thank you for your decking question, I think your idea sounds perfect for your space and once you complete your BBQ and seating area it will be a magnificent place to entertain! Our resident DIY expert @MitchellMc will be back online Friday to help assist, in the meantime I suggest checking out his great article and video on how to build a deck.

Community member @oninpena asked a similar question about their deck covering their drainage, Workshop team member@EricL gave advice that yes, it can be covered: "My number one suggestion is to integrate an access panel on your deck that will allow you to get to the drain in case you need to service it. You can either build a picture frame type system or have it blend seamlessly with your deck with a few discreet cuts that will let you lift a part of your deck panels." You can check out the full discussion here low level composite deck.

We would love to stay updated with your deck and other projects so please post photos of your progress.

Katie

MitchellMc

Hi @sanjurajan,

That sounds like a reasonable idea. I'd encourage you to have a look through the dozens of similar projects on the community. This will give you a good idea of the materials you'll need. You'll then be able to start your plan and work out how you'd like to construct your deck. The basic idea will be to fix joists at 450mm centres across the space. Your decking will then be laid perpendicular to the joists.

As long as your joists don't interfere with the flow into the drain, there shouldn't be an issue in covering it. Providing an access hatch would be a good idea, though.

Please let us know if you have any questions about your project that we can assist with.

Mitchell

sanjurajan

Hi,

Considering the amount of work to construct, the cost, and the yearly maintanence that goes with a wood deck was wondering if there are better options out there. Can you please throw some light on the alternate options that we have on the concrete alfresco ? Are tiles a good option(both cost to construct and maintain) for the alfresco concrete and if so, what tiles do we need to select to avoid slipping? Also, we have a step-down alfresco of about 180mm high (as shown in the picture above). Is there any way to lift the floor so that we have an illusion of an extended living room?

Thanks again

Sanju

KatieC

https://www.workshop.bunnings.com.au/discussion/comment/25005#Comment_25005

Hi @sanjurajan,

There are some great alternatives to a wood deck that could mean less maintenance over the years and ultimately save you money in the long run. @EricL will be online later this afternoon to better assist, but in the meantime, check out @jeffjen's seamlessly tiled outdoor kitchen makeover for inspiration, @Adam_W's timber-free deck with steel frame who used Ekodeck as an alternative to timber, or this thread tiling of outdoor deck where member @MazPert asks how to build his deck with tiles.

Katie

EricL

https://www.workshop.bunnings.com.au/discussion/comment/25005#Comment_25005

Hello @sanjurajan

One of the best decking materials you can use is Ekodeck. It requires very minimal maintenance, there is no need to sand, oil or stain as it is a composite material. It is built to resist termites, rot, decay, mould and mildew. It can be installed with traditional decking screws or you can use the Ekodeck Quickfix 3mm Quickfix Kit - Timber Joists to have a clean finish on your deck with no visible screws. It can be cut and trimmed like traditional timber decking.

As for the decking frame, the best defence you can apply to it is Consolidated Alloys 50mm x 20m Bearer Protector G-Tape. It is an acrylic adhesive flashing tape that protects the surface of the timber joist or bearer. Having a gap between the concrete and the decking frame is always a plus as it will not trap moisture directly under the timber itself.

In regards to tiling, there are a few choices from the Johnson tile range such as the Brunswick Pecan which has a beautiful timber-like pattern on top. Flooring tiles have slip resistance built into them. As for the 180mm drop, it will be necessary to build a brick or concrete base to compensate for the height difference. The other option of course is to do a combination of the two with the composite deck on the outside and timber-looking tiles on the inside.

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

Eric

sanjurajan

https://www.workshop.bunnings.com.au/discussion/comment/24587#Comment_24587

I have gone through similar projects and have come up with a rough idea(attached). It's not to scale though.

Deck_1 (2).jpeg

The basic idea is to cover the deck on a total area of 3900 X 4400mm ( Including the side concrete). So have joist of length 4400mm at spacing of 450mm. For the picture frame, there are double joists at the two ends spaced at 110mm considering the deck board width is 90mm. The joists are fastened to the alfresco concrete using L brackets (marked in pink).

Can you please check and let me know if this sounds reasonable to start with and let me know if I have missed anything major?

I have a few major queries to get clarified before I go hunt the materials.

1) The height of the internal floor to the alfresco floor is 180mm (please refer image in my previous post). If we use 90x45 Treated pine + 19mm deck, that leaves us with 71mm gap. Is it possible to use L brackets to raise the joists to ~71mm?

Or can we use this wider joist (140X45mm), plus 19mm thickness of the deck leaves us with a 21mm gap. Is that enough for ventillation and draining of water under the deck ?

This part is the most confusing to us even though we went through different discussions here. We also saw some discussions where people are using minifoot pedestals. Are they really required in our case or can we manage with the L brackets ?

2) Can I use this 4.8m length as joists? Or should I go for the 2.4m/3.6m lengths for ease of transportation? How do I join the joists if I go for the smaller length?

3) Also do we need double breaker sections for this length of the deck ? Do you see any structural issues with the design we have?

Thanks

Sanju

EricL

https://www.workshop.bunnings.com.au/discussion/comment/75196#Comment_75196

Hello @sanjurajan

Let me try to answer your questions.

The more space you have underneath your deck the more wind will be able to pass through under your deck. So 71mm is a good space to have.
Yes, you can use angle brackets instead of foot pedestals. The advantage of using foot pedestals is that they are easy to adjust. once you have the necessary height you can leave the pedestal in place. It will not turn once you screw the pedestal faceplate into the timber. There is no reason that you can't use both in combination especially if you have a sloping surface.
Yes, you can use the 4.8-length joist, I suggest counting the number of 4.8-meter pieces that you need and having it and the rest of the materials that you need to be delivered to your home in one go. I recommend speaking to the trade specialist at the store so that they can make a list of all the parts that you need down to the last screw. To join shorter lengths of timber, you can either do an overlap joint or use a steel plate in combination with a nut and bolt.
If you look at the lengths provided in the website list they start from 2.4m up to 6.0m and since you have a deck that is 4400mmlong it's best to get the 4.8m length even if you are putting in a picture frame. I recommend getting the Merbau pre-oiled panels to save you from having to re-stain the pine decking panel.
A double breaker decking panel design will not affect the strength of the deck. The purpose of the breaker board is to keep your deck boards straight and at the same length and control expansion and contraction while minimising the amount of wastage your deck may generate over time.

Here is an example of a breaker board design: Low-level composite deck over concrete slab by @Nat2

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

Eric

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