How to add drainage for low level deck?

[HayleyB1]

Hi there,

We are building a 2.6x4.5m deck in our back yard. My biggest concern is ensuring drainage.

We have a very small, low level yard so have to have the frame directly on the ground. We are using 75x100 H4 timber for the subframe.

We have dug out a slope from 140mm to 210mm towards the fence and plan to use crusher dust to fill the space and to lay the frame on top of. We have also dug out a trench at the bottom and lay 2 sets of agi pipe for drainage. Is this enough? Should we be doing more?

We are also doing 5mm spacing between the decking boards to allow for air flow

it began raining as soon as we finished digging the base and it hasn't stopped so we are currently pre-assembling the frame in the garage until the ground has recovered.

 

 

[EricL]

Hello @HayleyB1 

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

Although you are using H4 timber, I would still recommend lifting the frame off the soil by at least 20mm if possible. If it's not possible, I recommend using Gripset Betta 1L Waterproofing Membrane Bitumen Rubber on the bottom and sides of the frame. For the top section, I suggest using CAgroup 100mm x 20m Bearer Protector G-Tape.

These items will provide extra protection to the frame and extend its service life. Quite often when there is no ventilation under the deck, it greatly reduces the lifespan of the deck.

In regards to the drainage, I propose using a compacter to level the soil so that it does not hold or pool water. Make sure that the fall is directed away from the deck and into a proper draining area.  

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

Eric

[HayleyB1]

Thank you so much

We will try to use some pavers underneath to raise it up 20mm. And we need to compact the crusher dust so the water runs right down the incline instead of draining through or pooling?

Also, as you can see the area is very wet. Do we need to wait for all the water to drain before we lay and level the crusher dust?

[MitchellMc]

Hi @HayleyB1,

Adding the crusher dust will help compaction and allow you to slope the area towards the drainage. Provided the soil is not entirely waterlogged, you'd be fine adding the crusher dust now and compacting it. If the soil is just soft mud, I'd hold off on compaction until it dries out.

Mitchell