What drainage for retaining wall and paving project?

[Sebastian90]

Hi all, I’m planning a backyard paving + small retaining wall project (see pics). Would love advice on a few things:

1. Paving drainage – Do I need dedicated drainage, or will a gentle slope away from the house into the garden be enough?
2. If drainage is required – What’s the best type and placement here?
3. Retaining wall + pipes – There are pipes from the sink and another pipe that comes up through the roof (unsure what it is). Both cut across where the wall footing would go. Should I:
   - Leave them and put a ramp over that section (as shown), or
   - Re-bury/redirect them deeper so the wall can run continuous into the easement?
4. Agg pipe layout – I’m planning runs at points A, C, and E (see diagram).
   - Which way should each fall?
   - Do I need all three stretches?
   - Could E connect into the easement, or tie into the paving drainage instead?

Build context:

• Wall will be Adbri Versablock or besser block, paving on top.
• Ramp section (B) will be concrete.
• House is on a corner block, so there’s an option to outlet stormwater to the street at the bottom left.
• Extra pics show current site and the sink/pipes detail.

Any guidance on drainage setup and wall/pipes workaround would be hugely appreciated.

Thank you!

[EricL]

Hello @Sebastian90 

It's better to be safe in these situations and install dedicated drainage so that you won't get soil erosion as the rainwater will get redirected to your storm water. I propose using Everhard 3m EasyDRAIN Polymer Grate And Prejoined Channel, but if you are after something that can turn, I recommend running a French drain around your paved area. The plumbing pipes might serve a purpose, please consult a registered plumber just to be safe and ask them if they can be redirected or buried.

When building your paved area, I propose carefully planning it so that it has a slope going away from the house so that it does not turn into a catch basin. With the slope in place the French drain will catch all the rainwater flowing on the surface of your pavers. Your plumber will connect the agi pipe to your storm water drains, the plumber must be the one to connect it so that it is compliant with council rules. 

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations.

If you need further assistance, please let us know.

Eric

[Nailbag]

Hi @Sebastian90 

Nice to see you have put a lot of thought into your planning stage.

Following along the lines of a few of @EricL comments, I don't think you will need so much in the way of water catchment/drainage. If the ground is made to have a gentle slope away from the home you could potentially let the water run off naturally. And/or have in place a stormwater connection at the fall end thats capped off ready for a grate drainage system should it be required.

My last couple of reno's have had new exposed agg. driveways and paths and other wide areas and I have only ever needed one drain along my current garage as it's at the end of a fall. This has all been achieved by my very clever concreter who though follows my design, ensures his levels have various gentle falls that evenly distributes rainwater away, so there has never been a need for any further drainage.

As for that extra pipe that goes through your roof, thats a breather also known as a stink pipe to take away the smells from the sewerage plumbing. To have any pipes relocated if possible, your plumber will be the one to use. Same to setup any stormwater pipe connections as @EricL mentioned.

Nailbag

[Dave-1]

Good Morning @Sebastian90 

With the paving sloping away from the house and down the hill I wouldnt  be thinking hard about drainage, Tho I would be thinking about where teh surface water will run/etch the rest of the yard. The french drain that @EricL has mentioned might work well in that case. Tho you could also contour the grass area to slow/reuse the runoff so it soaks into your yard more then runs away.

The plumbing points you mention, I would leave them where they are or talk to a plumber about re-routing them. The "stink pipe" that @Nailbag mentions stays for sure  

With your concrete ramp are you going to put a handrail on the outside of it? Especially near the high point?

Your back door looks like you are going to close it off? I would check your local regulations as Houses need two doors, Front and back for exiting in case of fire. You cant have just the front door even if its a larger one.

I think the area will look pretty nice when you have finished it, love the drawing! 

Dave

[Sebastian90]

Thank you Eric!

[Sebastian90]

Hello @Nailbag!

Thank you for your message. I have a hard time visualising, would it be possible for you to indicate on the "plan" I provided where you would put the storm water connection and the grate drainage system (in the event I over engineer it)? I've had various internet folk tell me to put the grate where the paving meets the small retaining wall, but that doesn't make a huge amount of sense to me...

Much appreciated!

[Sebastian90]

Morning @Dave-1!

Thank you for your reply. Would you have the time to loosely sketch where this french drain would potentially go?
Yes- a handrail will be going in, and a small deck will be eventually put in place with stairs to the garden.  

[MitchellMc]

Hi @Sebastian90,

Given the sloping block, I'd be inclined to think that the majority of water will be flowing sub-surface downhill. I'd place agi-line behind the retaining wall at the base and backfill with gravel. That way, any water hitting the back of the retaining wall will be captured and directed to the nearest storm water pipe. It's just good practice to install drainage behind a retaining wall.

Provided the pavers are then graded slightly downhill away from the wall, any water hitting the paving should drain off.

Mitchell

[Dave-1]

Good morning @Sebastian90 

So the French drain I am thinking of is a gravl filled trench with an agi-pipe in the bottom of it. The gravel would be even curved like a dish. I would suggest to have it around the edge of the paved area and below that small raised retaining wall. With a few feeds away to a low point that can handle the run off. 

The hashed red curved is where I would put the French drain, the black arrow shows a pipe heading away to a low point under the surface. As @MitchellMc has mentioned drainage behind the retaining walls is always a good idea. You could join the two levels of retaining wall agi pipe so they can then run away downslope together. I prefer 100mm sizing as it fits nicely to the stormwater sized piping. I would try and reuse the water tho then send it to stormwater proper tho.

Dave

[Nailbag]

Hi @Sebastian90 

My thoughts were along the lines of @MitchellMc if that was clear to you. But then to have at the bottom right of the paved area a capped off stormy ready to add another row along the end of the pavers should the water run off from the pavers be too excessive.

Hope this makes sense?

Nailbag