How to build a deck with raised garden bed?

[maker_m82]

Hi all,

I’m chasing some advice on how to layout the substructure for my proposed deck, step and raised garden bed?

NOTE: This will all be freestanding, not attached to the house or the existing verandah.

I think I’ve probably read every deck post on this community but none have raised garden beds.

Would really appreciate advice. Specifically regarding…..

1. Single or multilayer substructure?

2. What size for bearers and joists etc.

3. Tuff blocks or stirrups?

4. What height is best considering I only have 200mm step at sliding door?

I’m sure there’ll be other questions to follow. Lol 

[EricL]

Hello @maker_m82 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your decking project.

To get you started I suggest looking at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. These guides will give you a good idea of what is involved in building a low-level deck. 

I also recommend looking at the Bunnings deck building guide:

• How to plan out your deck
   
• How to set out a deck
   
• How to install stumps
   
• How to install bearers
   
• How to install joists
   
• How to lay decking
   
• How to add a step to your deck.

Your decking project has quite a number of features that need to be overseen by a builder. The roofing structure, the raised garden bed and most importantly the possible installation of a firepit/fireplace. I propose engaging the services of an experienced builder and having a discussion with them in regards to your decking project. It might also be necessary to engage the services of an engineer especially if parts of your deck are to be attached to your home.

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations. 

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

Eric

[maker_m82]

Thanks EricL

I have updated my original post as I feel it may not have been clear enough.

Thanks for suggesting the pages you did. I have read a lot of these. However, none seem to cover the raised garden bed substructure.

Are you able to provide advice relating to my edited post?

Thanks in advance.

[Dave-1]

Good Morning @maker_m82 

A few questions to start with.

Your raised deck, how high is it going to be? You mention 200mm at the sliding door and the weep holes are 115mm to 200mm from the concrete slab?

Instead of building your deck to carry the load of the raised garden beds (which will be a fair load especially when wet) Why not build them on the slab  and save the added complexity an costing of being able to support those beds?

One way to save weight/soil in garden beds is to use styrofoam chunks in the base, depending on what you want to grow in them.

If the deck is going to be approxximatly 200mm high, then I would allow for more air circulation with the skirt that you have drawn around your deck. 

For 200mm height maybe tuffblocks is the way I would go, If you dont have to factor in the raised garden beds all the extras wont be needed. You could follow the layout spans from the span tables you have looked at.

Just had one last look at your questions, the height of the raised garden bed is 900mm from the deck and its only 400mm wide. That translates into being easy enough to push against to move. I would suggest to have it bolted to the slab or if you go the route of having it sit on the deck then bolted securly to the deck. Having it freestanding would also mean less chance from rot appearing compared to sitting on the deck long term.

Dave

[JacobZ]

Hi @maker_m82,

I'll start by just answering your questions.

1. With the height limitations, a single-tiered deck frame would be best. This means any connection from bearer to joist needs to be made with a joist hanger.
    
2. Due to the limited height, to have as much airflow as possible, I would suggest using 90x45 H3 Framing. I'm sure you're aware, but this will dictate what spans you can have and the location of your vertical supports.
    
3. There are 2 main options for support that you should consider. You can use these Builders Edge 70 - 170mm Bigfoot Xl Pedestal Feet, which can be adjusted up and down between 70-170mm. These would allow you to sit the bearers directly on the pedestal feet. You could also use either TuffBlocks or post anchors, but you would have to use a short 90 x 90mm Post on top to make up the height. This method would require you to cut and notch out the posts for the bearers to sit on.
    
4. Having the top of the deck flush with the sliding door is fine as long as you don't block the weep holes.
    

The main thing I would change in your current plan is to have the raised garden beds sit on top of the concrete instead of the deck. This is mainly because garden beds require water, and you don't want to have soil and water sitting on top of a deck frame, causing it to slowly rot.

I am more than happy to answer any further questions and work with you towards a more concrete plan.

Jacob

[maker_m82]

Hi Dave-1
 
Thanks for your response to my post. Much appreciated.
 
I plan was always to build the garden beds as a structure that didn’t sit above decking boards however the substructure of the deck would include vertical structure for the garden beds.
 
I like the idea of saving weight in the garden beds by using Styrofoam blocks. I have not seen this before. Could you give me more information or maybe a link that would help.
 
With respect to the deck skirt and more air circulation. Do you think I should increase the gap between the two boards or remove one board altogether? In my design I used two boards purely for aesthetics as I don’t want to see the substructure. What’s your suggestion?
 
 As for freestanding and being able to push against maybe I could attach the garden bed to the brick wall and pergola posts to provide a little protection against lateral movement. What do you think?

[maker_m82]

Hi JacobZ
 
Thanks for replying. I have further questions. 😁
 
1. If I use 90x45 h3 framing, do you know what the span and spacing would be when used as bearers? 
According to “AS 1684.4—2010 Residential timber-framed construction - non cyclonic areas, fig A2 bearers supporting floor loads only (40 kg/m2)” the closest offered is 2/90x35.
 
2. If I’m required to use 2/90x35 bearers then tuff blocks or builders edge pedestal feet are out because they don’t support 70mm width. Neither do most post stirrups. How do I get around this? Obviously if I use 2/90x45 bearers I can use most post stirrups but again not tuff blocks or builders edge pedestals.
 
As for the garden beds, I agree. They are going to be their own structure but share the deck substructure. Ie. the deck will run up to but not under the garden beds and the substructure will support both.

[maker_m82]

Also, can someone tell me if I’m referencing the right standard for this? 

Im using AS 1684.4—2010 Residential timber-framed construction - non cyclonic areas.

[EricL]

Hello @maker_m82 

AS 1684.4—2010 is generally the right standard to use for residential timber-framed construction in non-cyclonic areas. If you're using 90x45 treated framing timber, this size is commonly covered under that standard. However, requirements can vary depending on your specific location and the details of your project, so it’s important to confirm with your certifier, local council, or a qualified professional to make sure you're referencing the correct version and applying it appropriately.

I also suggest having a look at this featured project - Low-level composite deck over concrete and soil by @oninpena. It's a good example of a single level frame that uses angle brackets and pedestals. Perhaps its simplified decking frame design can be used for your project.

If you need further assitance, please let us know.

Eric