How to build a low-level deck with 100mm clearance?

[jinugu]

Hello experts

I am undertaking a decking project, a DIY. Low level deck with a ground clearance of 100mm or so. Attached is the proposed design. 

Posts would be 400 mm length with 300mm underground.

Any suggestions or advice pls.

The bearers will be placed flat on the posts and the decking board on top.

Best regards

RaviDraft design

[JacobZ]

Hi @jinugu,

Thank you for reaching out for some guidance with your decking project. I'm excited to help you out with this project.

As a starting point, I think you should have a read through How to understand deck components and How to understand deck span tables as they give all the information that needs to be considered when designing a deck.

I like to hear that you are going to use posts concreted into the ground. This will give you a nice sturdy deck that is well supported. When you say the posts are going to be 400mm in length with 300mm in the ground, are you saying there will be 100mm above the ground?

If so, you may need to rethink this because you can't sit a bearer directly on top of a post; it has to be attached to the side of the post using bolts. The standard is to have the post notched out so that the bearer sits on it with two bolts going through the bearer and post to lock it in place. This ensures the weight is supported by the posts, not the bolts.

Another thing to note is that Ekodeck must be supported every 450mm. If you are running the boards vertically between your bearers, they would span almost double this at 850mm. This would not be a safe deck.

My suggestion is to revisit your design and add some joists that run between the bearers. If you use 140x45mm framing timber, these joists can span up to 2600mm between bearers, meaning you would only need 3 runs of bearers. Something like this would work.

A design like this would ensure you are building your deck safely and suitably and are in line with the deck framing span tables and requirements of the Ekodeck.

Let me know what you think and if you have further quetsions, please don't hesitate to ask.

Jacob

[jinugu]

Good morning Jacob Hope you had a good weekend.

Thanks for the reply.

Yes, the post would be concreted for about 300 mm in the ground and will stick out approx 100 mm above the ground 

I take your advice.

Do you think it would be ok for the joists to be screwed into the bearers or will I have to use joist hangers. It would be easy for me to screw them in rather than using joist hangers. 

Your help and advise is very much appreciated.

Thanks

Ravi

Best regards 

Ravi

[JacobZ]

Hi @jinugu,

Joist hangers are specifically designed and tested to carry vertical and lateral loads. Screws alone, especially standard wood screws, are not load-rated and cannot safely transfer these forces.

To create a structural connection, you'll have to use joist hangers with these Pryda Timber Connector Screws.

Let me know if you have any further questions.

Jacob

[jinugu]

Hi Jacob

Based out of your design, would the below work? I presume the spacing between joists is 450 mm.

As a side question,  if I want a mimosa pergola  of approx the same dimensions span the deck, how would you suggest i fix its legs?

90 x 22mm Decking H3 Treated 

Best regards

Ravi

[EricL]

Hello @jinugu 

I propose choosing your pergola first and making sure that its footing and installation are compliant with local council rules and regulations. This makes the pergola a self-standing structure that is not linked to the low-level deck. Once the pergola is in place you can then build the low-level deck underneath the pergola. Please make sure to check the rules and regulations in regards to deck height and pergola roof clearance.

If you need further assistance, please let us know.

Eric

[jinugu]

Hi Eric

Thanks for the reply.

I was given to understand by a tradie that the pergola could be bolted to the same posts (800 mm under the ground) that I would use for the decking. From your advice, that's not recommended. 

Do you recommend using concreted footings instead?

Best regards

Ravi

[JacobZ]

Hi Ravi, (@jinugu),

It is best to keep things separate, as permanent pergolas will often require submission of engineering plans to your local council, and the standard plans for pergolas will not take into account construction over an existing deck.

I would recommend doing some research on the type of footings your particular pergola requires.  It will be dependent on the specific pergola you use, but concrete footings are common and likely a good option.

Let me know if you have any further questions.

Jacob

[jinugu]

Hi 

I was referring to this one, which is a semi permanent structure.. Mimosa 3 x 4m Lava Portsea Louvre Semi Permanent Gazebo - Bunnings Australia

Doesn't appear to require council's approval?

Best regards

Ravi

[JacobZ]

Hi Ravi (@jinugu),

It will depend on your local council's rules, but they often require council approval. We have copies of the engineering plans for these semi-permanent gazebos that we often send to our members. 

In the engineering plans for that particular gazebo, it's noted that a cylindrical concrete pier underneath each post, 450mm in diameter and 600mm deep, is suitable for this gazebo.

If it was attached to a deck and you were required to submit plans for approval, you would need to have it reassessed by an engineer to ensure there is a suitable foundation. It would be much simpler to install the gazebo using separate foundations to the deck.

Let me know if you have any further questions.

Jacob