Drainage around boulders and side of house

[Glyph]

Hello all, I am hoping to get some advice from some drainage masters.

I have a split level home on a steep block. On the east side, where the house steps down, we have a brick retaining wall behind our carport, and some large boulders. Water from the upper carport/garden bed often flows down the boulders and along the side of the house and against the bedroom wall where we have a couple of vents. Puddles of water are often sitting at the bottom of the boulders and leaving the soil/gravel right next to our house wet. This has all been compounded by our neighbours new concrete fence which is acting as a giant moisture barrier, trapping things on our side.

We have had an agi-drain installed along the fence, however it doesn't go up past the boulders. I have laid large slate pavers and gravel to keep the side area reasonably permeable but the issues is the far corner. I am seeking some guidance on the best way to address this.

- Do I add another agi-drain right along the house, to prevent water running close to the walls/vents.

- Do I add an agi-drain along the boulders, so water that runs down these gets absorbed?

- Do I just try to improve the fall of the ground around the boulders, to help guide the water further down?

I would appreciate any guidance.

Side of houseBoulders and problem area on right

[Jason]

Hi @Glyph,

Welcome to the Bunnings Workshop community. We trust you'll get loads of helpful advice and plenty of inspiration for all your projects around the house and garden from our amazing members. 

Our resident Bunnings D.I.Y. expert @MitchellMc is taking a break today but will be back on the site tomorrow to share his thoughts on your drainage issues. In the meantime, let me tag knowledgable members in @Adam_W, @JDE, @Brad and @TedBear to see how they might go about tackling the problem.

Thanks, and please let me know if you ever need a hand getting the most from the site.

Jason

[Brad]

My gut feeling is to add drainage against the house wall, not sure if that is the best idea as my experience is a bit limited in drainage.

[Glyph]

Thanks @Jason I appreciate it, looking forward to it.

[TedBear]

Hi @Glyph   I have had to solve a wet courtyard issue a few years ago (mine was brick paved but it didn't have a stone "waterfall" involved like yours. My house footings were getting wet and starting to get crumbly, and the flooding across the paving bricks would make its way into my garage.

My answer was (& my recommendation to you) to dig a trench along side the wall just deep enough and wide enough to hold a slotted pipe (plus a bit more) and then pour small loose stones (eg blue-metal perhaps) around and over it - to match those in your surroundings. This will allow the water to run into the slotted pipe from the sides and from above if it pools. It might be a good idea to do both sides if the area is very wet, so as to protect the concrete wall too. Run the pipe/s to a soak well a little further down the hill - or even at the bottom that area. (I assume that the down-pipe in the corner must be running to one anyway, so maybe you can direct the pipes to it. There shouldn't be a big flow from the slotted pipes, more just a trickle over time after rain.)  This will unobtrusively collect excess water before it gets to soak the wall footings. 

Why not do all 3 of your suggestions?  -

If you cement in some stones at strategic places you should be able to guide the water from above to make its way down the centre of the stone pile and keep away from the edges. From the picture, it looks like you'd only need 3 or 4 small stones placed on the right of the pile, where the stones tilt toward the house.  Then it can make its way to the drain/s, either flowing across the top or soaking through the soil.

My house wall has been good since I put the drain next to it and the bricked area no longer floods at all when it rains.

I hope this description makes sense.

TedBear

[MitchellMc]

I see you've already received some excellent advice from our knowledgeable members @Glyph.

To add to these fantastic suggestions, I'd recommend installing an Everhard EasyDRAIN Polymer Grate & 1m Channel at the top to capture surface water before it gets to the slope. I'd imagine a lot of the water coming down the slope is subsurface, so you might like to employ some other methods mentioned here to capture that, and the slotted Agline sounds like a good idea. Since water is obviously permeating out through the rocks, a secondary slotted Agline at the base of the rocks should capture any excess. Both the line from the top channel and the bottom slotted line can be diverted it into that stormwater drain.

I'd also recommend painting a waterproofing coating over your wall down the sloped section. For an extra layer of protection you could paint the bottom couple of courses of bricks on your house's wall as well.

What's the subsurface pipe coming out of the slope?

Please let me know if you have any questions.

Mitchell

[Glyph]

Thanks for this @MitchellMc I like the idea of the ag-drain on the upper side and connecting that into a new solid line. This could also just run along the brick wall and meet the other connection you can see half up the existing down pipe.

One thing that has perplexed me about these ag-drains, is how well they actually work. I understand the small slots allow the water in, and it fills and moves water down the pipe, but what prevents this water from not just leaking out of the slots again? How much water really gets moved?

Re the waterproof coating, is this clear so it's not noticeable on the brickwork, or does it have a color? I have some existing membrane paint but it's solid black. 

Thanks again.

[Glyph]

Thanks @TedBear I like the idea of some more positioned stones to guide the trail of the water. Two ag-drains might make sense, to cover my bases. If I'm going to dig the area up, I might as well go all out.

When you did your house, did you use a textile membrane/fabric to wrap the stones and pipe? I have read that this helps prevent soil contaminating it? Or is it ok to just use the aggregate on its own in the trench.

[MitchellMc]

Hi @Glyph,

The idea with the slotted Agline is that most of the water will take the path of least resistance. Given adequate fall on the pipe, the water will run to the lowest point. Some does still leak out the bottom, but the bulk will be transferred. I've designated the points where the slotted drain should be used for collection but switch to non-slotted when transferring.

If you wanted a clear waterproofing product, I can suggest the Crommelin 4L Brick And Render Water Based Sealer.

Mitchell

[TedBear]

Hi @Glyph I just used the aggregate to keep soil out. In my case, I needed edging for the paving bricks, so I inserted 1/2 slabs vertically, dropped the pipe in and surrounded it with stones. (photo). It carries water away immediately. I'm sure a small amount falls straight through, but its the larger flows that do damage. I guess you could line the bottom half of the trench with plastic to create a barrier there, before adding the pipe and stones.