How to build a French drain?

Glorz

Hi all,

looking for a bit of advice on how to do a French drain. I've done a bit of research on them and I'm looking to lay one down on my front yard and connect it to my stormwater pipe for some drainage as my yard slopes towards my house causing rainwater to run towards my house and sometimes puddling at the lowest point (Pink X is on picture) plus lawn feels damp even days after it has rained. Hoping to get some guidance on it and what materials to use and whether my ideas are achievable or not.

This is the current state right now. Soil has built up on the far right of the house which I know is not good at all. Im going to dig down so that it's in line with the lowest point (PINK X)

the BLUE LINE is my current stormwater pipe, and the YELLOW LINE is the ag pipe I'd like to run across my lawn. ill have to cut the concrete to do it. I'm thinking of then putting a pit where the red square is.

my question with the the above PIC 1

1. Does this look okay to do?

2. How far away from the house do I need to dig my trench? im thinking around 400mm away from the house and have the remaining soil thats near the house, slope towards the trench.

3. what width does the trench need to be and how far down do i need to dig

4. what materials would you recommend?

5. would i need to also build a retaining wall due to the drop that will happen once i level it down to the lowest point? as im only going to level about a metre from the house so there will be a drop.

this is a example ive drawn up of what Id like to achieve. either a retaining wall and pavers with french drain underneath OR just the pavers and french drain

Pic 2 - Retaining wall to hold up sloped area

Pic 3 - no retaining wall but then there will be a drop 

Thank you and apologies if this is a very long post. Im very excited to start a new project and any advice would be much appreciated. 

EricL

Hello @Glorz 

Thanks for sharing your question regarding putting in a French drain. Generally speaking, if you were to install a French drain near your house, I propose looking at  Vinidex 100mm x 20m Socked Slotted Draincoil along with Geotextile. I would suggest making the trench around 200mm deep to accommodate the Geotextile, draincoil and gravel. This is on the condition that the fall is correct, otherwise a deeper trench will be required.

However, due to the complexity of your proposed drain system and that it involves proximity to your house wall, I suggest engaging the services of a registered plumber. Using a professional trades person means that any rules on run off regulations will be observed, and joining on to your storm water drain will be done to code. You can still save on this project by doing all the heavy lifting, digging and concrete cutting.

If you are building a retaining wall right next to your house wall, I would also recommend engaging the services of a builder. They will be able to guide you on how to protect your wall from moisture ingress, insect and termite infestation. It would be technically easier if you did not have to build a retaining wall and just provide a fall for the drain.

I propose showing your plan to a registered plumber and they will advise you on the distance the drain needs to be from your wall. You may also ask them about your proposed location of the drain pit.

Here are some handy discussions regarding drainage:

• How to fix a muddy lawn by @Adam_W 
   
• Drainage to fix a muddy lawn by @Ben 
   
• Do you need drainage on each side of the house? by @oasis1frog 

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

Eric