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I am looking to utilise the space under our current deck for another decked area extending to the fence to increase the pool area (moving fencing back which will cut across new deck area)
The issue I have is clearances, the current under deck height is 2100. Therefore the preferable height would be for the deck to finish level with pool slab which is 100mm from ground.
In order to do this I am aware I would need to dig down. I was planning to use joints on tuff block to keep it as low as possible. Although the under-current deck area will be sheltered by the top deck and roof from some rain I am still concerned about pooling under the deck if it effectively sits in a pit. What would you recommend for drainage solutions? or is this overall an unworkable idea?
At the moment, it looks like you’ve essentially created a low point where water collects @dave_022, which is why it’s pooling so badly. A sump and pump could work, but it’s worth considering whether there are simpler ways to manage the drainage first.
For example, what’s to the right-hand side near the shed? If possible, you might be able to dig a short ag line there to divert some water away into another part of the yard. Also, the lowest point appears to be down at the fence. If the aggregate base is levelled correctly, a lot of that pooling should reduce naturally. Once your paving is installed, water won’t penetrate as easily and will mostly run off, especially if you grade the paving slightly towards the backyard.
Given the current water level, I’d recommend building up the aggregate so the top of the base sits at or just above the current water level. Then when you lay your paving, it will sit higher than the water, so even heavy rain shouldn’t cause pooling on top of the pavers.
Essentially, ensure the aggregate is raised enough to give the water somewhere to soak in without sitting on the finished surface.
Mitchell
Thank you for the advice. Since my last post it has rained some more which has been more telling. Given enough rain the whole area fills up.
As seen in the photo we intended to level the pavers with the path next to the wall and adding road base to the water level would create a step up to this.
I think a large part of the problem may be the downpipe wchich runs on to a paver and basically into the hole. I am wondering if this was re directed into some ag-pipe running to the back o the garden this may help? I just wish there was a way of getting it to the front of the house as there is a 400mm drop to the. road that side....
Thanks for the extra detail, @dave_022. That extra rain has definitely helped reveal what is really going on. From what you have described and from the photos, the downpipe discharging into the low point is a major contributor to the problem. In heavy rain you are not just dealing with groundwater or surface runoff, you are actively feeding stormwater into an area that already has nowhere to drain to, so it is no surprise it fills up quickly.
Redirecting that downpipe into a properly laid stormwater line would make a significant difference. Running it into ag pipe that daylights somewhere lower in the garden could help a little, but ag pipe alone is not ideal for roof water as it can silt up and it still needs a clear discharge point. If there is no way to get it to the front where you have that 400 mm fall to the road, then your options become more limited and more “engineered”. This is where either a new stormwater connection, subject to council approval, or a sump pit with an automatic pump starts to make sense, particularly if the area is already acting like a bowl during prolonged rain. You could potentially take the stormwater pipe at deck level and send it down the side of the house to the road. It would be attached to the side of the house. With that height and amount of fall you might be able to atleast send the the water from the roof to the road.
You are right to be cautious about building up road base and creating a step or changing levels around the path, as that can create new problems and still will not solve the core issue, which is water evacuation. Before spending too much more time or money, I would strongly recommend speaking with the council’s drainage or engineering department and explaining exactly what is happening. They can advise whether there are any legal downhill connection points available, whether at the rear or side, or whether a pumped solution is acceptable in your area. It is frustrating, but once you have a compliant way to get that roof water out of the yard, the rest of the drainage issues around the deck become far more manageable.
Mitchell
I did have a thought as I walked round the pool. Could I connect the two down pipes as shown and direct all roof water from that side into stormwater?
The white pipe is not overwhelmed and then I would only need to sort out the water that falls directly on the garden,,,
