To build a low level timber deck approximately 25 cm of the ground

[Chye]

Hi, I plan to build a low level deck, 8.5 meters long, 3 meters wide on one side and 3.5 meters on the other. To cover the 8.5 meter length on the front I plan to use 125x75 treated pine as the bearer whilst I plan to lay a 75 x 100 bearer flat on gravel or supported with concrete pavers in the middle and close to the house wall. The 100 x 50 joists will be screwed into the bearers laying flat and then attached perpendicularly to the front bearer with joist holders.

Is this workable? will this be stable and secure enough? I'd appreciate some feedback about laying the bearers flat on the ground from anyone who have done this before.

Thank you for your help.

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

Chye

[Jason]

Thanks for joining in the discussion @Chye, we are looking forward to seeing your decking project take shape. 

Let me tag a couple of very experienced deck builders in @Adam_W and @ProjectPete who might like to share their thoughts on your design. 

Please note I edited your post and flipped your plan as the image was reversed. Let me know if you ever need a hand getting the most from the site.

Welcome,

Jason

[ProjectPete]

In short,

• 140x45 H3 timber is sufficient for bearers provided your posts are appropriately spaced.
• 120x45 H3 is perfect for joists.
• Anything touching the ground or even "sitting on concrete ledge" where moisture is present needs to be H4.
• The joists can't just "sit on a ledge", they need to be fixed to the frame/structure.

[Chye]

Thanks for the tips Pete. I will make the changes.

Regards,\Chye

[Chye]

Hi,

a bit disappointed today: went out to Bunnings this morning hoping to make an order for my requirements only to be told that Bunnings do not sell treated pine H3 in 120x45 size!

According to the staff in Bunnings, it has to be 140x45 which is what I am using as the bearer which will prove too costly or the 90x45. would a 90x45 be adequate as joists?

Any suggestions?  

Thanks 

Chye

[MitchellMc]

Hi @Chye,

I'm sorry to hear that the sizing of 120x45mm H3 treated pine was not an option available to purchase. After the weekend, I would be more than happy to make enquiries with your local stores to see if there is a possibility of placing a Special Order for the timber.

Let me mention @ProjectPete to see if he can qualify whether 90x45mm would be adequate for joists.

Mitchell

[Chye]

Hi,

I have been told that H3 treated pine does not come in 120 x 45. If I use 90 x 45 size joists, it is recommended that I do not span more than 1.2 meters. I am considering using 140 x 45 as joists. I have not seen any literature on this so would like to check with the group if I use that size joists, can I span 3 meters?

Thanks for the help.

Chye

[DopyDingo]

Hi @Chye 

Sounds like an amazing sized deck. 

One thing to consider in your planning is the weight and potential sinkage.

This size deck will be quite heavy and depending on the type of soil you have (Sandy, clay etc) you could have sinking over time due to rain etc if you place the the bearer directly on the ground.

I know you mentioned you were going to use pavers in the middle but consider placing other supporting measures on the furthermost point from the house also as this will help disperse weight and reduce movement over time.

Looking forward to seeing the outcome!

Dean

[MitchellMc]

@Chye,

With considering the costing as you had mentioned earlier, instead of using 140 x 45mm as joists you could potentially run two 140 x 45mm bearers down the middle of the deck and use 90 x 45mm as joists. That way they would only need to span 1.1m. I'm thinking even 1.1m is possibly too wide a span for 90 x 45mm. Perhaps @Brad might be able to qualify that for us.

If you are going to use 140 x 45 joists on the current plan with a bearer down the middle, that joist would be spanning 1.5m and not the full 3m unsupported if I understand correctly. If the deck had more than one bearer down the middle it would open up the possibility of more options sizing-wise.

Mitchell

[Chye]

Hi Mitchell,

those two options are what I am considering doing:

1. running an extra bearer with 90 x 45 joists as you suggested or

2. using 140 x 45 joists and not having any support in the middle, hence the span will be 3 meters

Not sure which would be a better option - cost -wise as integrity - wise

Chye