How to add drainage?

I have an area where I’d like to concrete and need input/advice on how to manage water drainage effectively. Additionally, I’m seeking advice on sequencing the work—fencing, plumbing, concreting, and patio installation.

Photo 1: The plan is to replace the timber fence with a lapped privacy fence and concrete the area. There’s also the potential to add a shed on top in the future, so I’d like to keep that as an option. I need a drainage solution and advice on how far the concrete should extend towards the fence. Please note that my neighbour’s land is about 200mm higher than mine, and bricks serve as a retaining wall. Since I recently purchased my home, I’m keen to ensure my neighbour’s land doesn’t flood, as the soil is against my brick wall. The drainage solution should prevent water from being trapped anywhere.

Photo 2: A four-post patio with a roof is planned, as indicated by the white-marked area on the land (note: the black striped area represents the concrete without the patio).

Challenges/Considerations:

The elevation of my neighbour’s land is around 200mm higher than mine.
My fencing contractor suggested placing a sleeper at the bottom of the fence to act as a retaining wall. However, I’m concerned this might cause water to accumulate against the front of my house (as the 200mm raised land runs along the entire house wall). It’s in my best interest to divert as much water away as possible.
I currently experience pooling in various areas of my lawn, particularly in the section shown in Photo 1, during heavy rainfall.
My land is almost completely flat, with minimal slope. A plumber suggested a subsoil drainage system with a sunken pit and pump for $14k.

Questions:

My main priorities are to replace the fence, install the patio, and address property drainage. However, I’d like to establish a comprehensive drainage plan now to avoid any issues or rework later on. Key questions include:

Should the fence have a sleeper at the bottom, or could this interfere with water flow from my neighbour’s property, potentially affecting my house walls?
Would a subsoil drainage system work in the area where I plan to concrete and may eventually add a shed (see Photo 1), considering it would be beneath the concrete? If not, should I install a drain channel, or is there a better solution?
Can I handle the lawn drainage myself? The $14k quote seems quite steep!

P.S. The stormwater drainage from the roof (existing and patio) will be addressed separately. This post specifically concerns drainage of surface water not captured by the roof.

Thanks in advance!

Photo 1.JPG

Photo 2.JPG

Photo 3.JPG

Regards,

Sandra

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @Sandra713. It's brilliant to have you join us, and many thanks for your question about drainage.

From what I can see in photos one and two, I recommend stopping the concrete approximately 100mm from the fence. This gap will allow for proper drainage and prevent water from running directly into the fence. While installing a sleeper at the base of the new fence can help hold back your neighbour’s soil, it’s important to avoid creating a situation where water accumulates against your house. To manage runoff from the slab, you should install either a surface drain or a subsurface drainage line in the gap. A subsurface drainage line will require filling the last 100mm with aggregate, allowing water to filter down into the drain and be redirected away.

For the lawn drainage, the extent of standing water is key to determining the solution. If you're only experiencing minor pooling in areas you won’t concrete, running a subsurface drainage line around the perimeter of the new concrete area should help collect and divert surface water into the stormwater system. This would also address water runoff from the new concrete, which would likely flow onto the adjacent lawn. Ensuring the drainage system is in place now will prevent future rework and reduce the risk of water pooling.

If you’re comfortable with D.I.Y., digging the trenches and laying the drainage lines yourself could be a cost-effective solution. However, I’d recommend consulting a drainage expert to handle any necessary connections to your stormwater system. It would be worth getting a few more quotes to ensure you're receiving the best advice and pricing for the job.

Please let me know if you have any questions.

Mitchell

Sandra713

https://www.workshop.bunnings.com.au/discussion/comment/42621#Comment_42621

Thanks a ton Mitchell! I think I'll love the Bunnings Workshop community 🙂

Could you repost the two hyperlinks please. I get "This site can't be reached" when I click on it.

Could you clarify what you meant here ' While installing a sleeper at the base of the new fence can help hold back your neighbour’s soil, it’s important to avoid creating a situation where water accumulates against your house.' Is you point that the sleeper will block off the neighbour's soil which is also a water 'sinking/draining' path (horizontal) when water piles up on the lawn when it rains? Or did you mean something else?

If I chose a subsoil drainage system between the concrete and fence (see photo 2 - where I may put a shed in the future) where would the water ultimately go - what options do I have?

Your comment "Ensuring the drainage system is in place now will prevent future rework and reduce the risk of water pooling." Could you clarify? Do you mean put subsoil drainage solution into the ground now and before the concreting? Why risk for rework?

I recall someone once telling me to not join the stormwater with the subsoil drainage system. I can't remember why.

I am comfortable with comfortable with D.I.Y (for a $14k savings I definitely get motivated), however, how will I find out where to route the subsoil drainage through my lawn. What if i decide to plant palm trees.

So many questions..... 😉

On a side note: can I get in touch with other members of the community? If so, how do I do that?

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/83429#Comment_83429

Hi @Sandra713,

Not sure what is happening with the links that @MitchellMc posted but surface drainage is made with drainage channel and its accompanying accessories and subsurface drainage line is agi pipe and its accompanying accessories.

I would suggest that your project sequence should be fencing, plumbing, concreting then patio installation. This is because fencing and plumbing both require digging, but the fence is concreted in place and will not move once installed. If you were to do plumbing first, digging for the fence could disturb drainage lines if they were installed first.

I believe what Mitchell meant when saying "While installing a sleeper at the base of the new fence can help hold back your neighbour’s soil, it’s important to avoid creating a situation where water accumulates against your house" is what you have said. If you install a sleeper there, it will act as a dam preventing water from naturally draining under the fence. Due to the lay of the land, it is likely unavoidable, so I'd suggest installing the sleeper but ensuring adequate drainage is installed here.

If you use subsurface drainage in the form of agi pipe, drainage gravel and geotextile membrane, the agi pipe should be connected to a stormwater line that flows to the street and into the council stormwater system. There is no reason that I'm aware of that you can't connect subsurface drainage to your stormwater line.

With surface drainage, the drainage channel should run to a drainage pit that is subsequently connected to the stormwater line.

Please note that both solutions will require the assistance of a plumber to make the final connection to your stormwater line as you need to be licenced to plumb into the council stormwater system.

The comment "Ensuring the drainage system is in place now will prevent future rework and reduce the risk of water pooling." is because now is the best time to install drainage. Installing it after everything is in place would be considerably more difficult.

You might like to check out How to install garden drainage for some guidance.

You might also find some benefit in looking through these previous discussions about similar projects:

If you want to get in touch with other members of the community you can click on their profile and scroll down where you will see a button to send a private message.

If you want to tag people in discussions, simply put an @ symbol in your comment and then type their username.

Some of our wonderful members who are always willing to help include @Dave-1, @Noyade and @Nailbag.

Please accept another warm welcome to the Bunnings Workshop community and let me know if you have any further questions.

Jacob

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/106626#Comment_106626

Good Evening @Sandra713

Nice bunch of questions 🙂 And then your photos really show what you are describing.

I really like @JacobZ's enlarging upon the how to especially the stormwater .

The sequence of jobs is

Fence

Drainage/concreting ( I have put them together as I have an idea in my head for the drainage channel)

Id actually leave a little larger gap between fence and your concrete, maybe 200mm or 250mm. It gives a space you can work if you need to down the track mainly.

I would definently get the slab laid by professionals, considering you are going to be putting a gazebo on part of it, nothing worse then a crack appearing across your slab.

So back to drainage and the concrete, The Grill drain that has been described is the one id choose as well (I am about to install some for my place strangely) The way I would install it is looking side on to your fence line, Fence, 200mm gap, then the grill drain but it will sit lower then the concrete slab, say 20mm lower. This way it wont matter what your neighbours water situation is, you will have something in place to handle it.

The Grill drain Id be tempted to run around the whole edge of your patio and connect it to the stormwater at two points. (I can see your downpipes so the piping is there). The grill drian dosnt need to be concreted in, but id probarly make sure there is a small gravel base for it to sit on.

Some things to keep in mind -

- since you will be concreting up to the edge fo your house, expansion foam? strip? will be needed against the house.

- Make sure your stormwater pipes are in good order (plumber can check with a camera for breakages/blockages will cost some $$ but worth it, at the same time you can ask about stormwater points for your grill drain)

- Gazebo water runn off, downpipe to?

- The concrete slab may have a sligh fall away from the house so water runs away from the edge of your house.

- A drainage pit?, your stormwater must exit your property by gravity as you havnt mentioned a pump. Have you got a photo of the gutter out fron on the road where the stormwater comes out or where you suspect the stormwater to go? I am just trying to think of why you would need a pit is all.

Dave

Sandra713

https://www.workshop.bunnings.com.au/discussion/comment/120509#Comment_120509

Thanks you Dave. I much appreciate your feedback. You are the first that mentions expansion foam and I'll definitely now keep that in mind as well as all the other tips.

My lawn is very flat and there's hardly any slope. That's the reason for a pit and pump. However, I have a plumber and drainage specialist coming on site on Monday with the camera so I shall soon found out what the situation is and whether it's a simple solution to get it running again.

Thanks again a ton that you've taken the time to respond.

All the best with your upcoming projects, whatever they might be 🙂

Regards,

Sandra

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