Help needed for building deck

Good evening.

Me and my missus are looking at building decking. See attached pictures for planning.

We're looking at using 130-140 mm by 19mm planks for the decking.

We would like it to be flush with the ground but I am having trouble finding good ways to set up drainage(water pools in this area).

Is there a way to do drainage without costing a fortune or is it better to ditch that idea and have it elevated?

Of course we're going to use a lot of drainage gravel, even under the concrete posts on the underground structure.

On top of that is it structurally okay to use 3 inch screws to fasten to decking to the support structure and to hold the support structure together or should I use other dimension screws?

If we do it flush I don't think a thick layer of gravel and the 8mm gaps in the decking will be sufficient to prevent flooding, but of it's elevated 19mm with lots of gravel will it still flood expand and rot? And will lacquer prevent this?

Sorry for the rambling I'm looking for general tips as it's my first time building a deck, and I want it as a fun project to work on with my missus, as well as saving us 100s and 100s of dollars

Any feedback welcome. Thank you in advance.

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Comments

EricL

Hello @Kieljustin

Welcome to the Bunnings Workshop community. It's magnificent to have you join us, and thank you for sharing your question about building a low-level deck.

It's great to hear that you've decided to build your own low-level deck. Your concern with drainage is well-founded, as you know if there is too much water or moisture under your deck it will shorten the life span of the whole structure. Would it be possible for you to post a picture of the proposed site? We'll get a better idea of how the area is laid out. We can then offer you recommendations on how to proceed.

It's good to see that you've been making plans. I suggest reading this guide - How to build a low-level deck by @Adam_W. This guide will give you basic ideas of how to plan your deck. Another point of discussion will be the space in the area. What is the space between the concrete slab and the soil? What is the gap between your sliding door frame and the cement floor? How big do you want your decking to be?

It's perfectly ok to ask questions about your deck. However, some questions need to be answered first before any other question is brought forth. For example, what size timber framing have you decided to use? Will you be using pedestal feet or use timber decking posts?

Here is a link for ideas and inspiration: Inspiring low-level deck builds.

Here are some amazing low-level deck projects our Workshop members have shared:

Low-level Merbau deck over concrete by @DIYImpressions.

Low-level deck with steps and lighting by @asifkhawaja.

If you need further assistance, please let us know.

Eric

Adam_W

Hi @Kieljustin, sounds like a great project and you are certainly taking into account the potential issues.
There are two main issues when it comes to ground clearance - water rising and saturating the timber on a regular basis (obviously not much you can do about occasional, irregular flooding) and maintaining air circulation as this is what keeps humidity down and lets it dry out if or when it does get wet.
Removing a layer of soil & replacing with drainage is highly recommended simply because drainage gravel doesn't retain moisture so isn't sitting wet close to the timber but... if, as you mention, water pools in this spot then that won't change. You need to be sending the water elsewhere.
Assuming you have some way to achieve fall then a simple sub-surface drain can fix this pooling problem.
Short version... dig a trench with a slight fall to some place where you can take the water away. Lay a slotted ag' drain pipe, cover this with gravel and then lay your gravel bed.
In these situations the decking frame (bearers & joists) are best supported on galvanised steel stirrups and your timber then bolts to these.
You might find this recent boardwalk post of mine useful as I had to install a small drain in it.

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