drainage and water under house - prevention ideas please

[hopetown]

Hi team.

House built on piles on slope, into hill.

So clay backyard is a bit higher than the bottom of the piles

Yard
--------------
_______Piles (and under house) _____________

Water rolling down from property above. Going under house.

Ideas to prevent water entering subfloor?

Obviously I should install drains before water reaches house. And I will.

But as a backstop? In a worst-case scenario where drains don't cope?

Should I board off bottom of house and waterproof? With a drainage channel around perimiter?

If so, best products/ techniques to use?

Anyone tackled this kind of issue before?

Would love to hear ideas and advice?

Or the names of contractors in Auckland who may know how to deal with this issue.

Please ask if you need other details etc.

My goal is a bone-dry underhouse. Is this achievable?

Thanks for reading.

[PC]

You need some where for the water to go.
Drainage provides an easy flow path.
Just trying to stop water is difficult & more expensive.

Drainage - around outside + drainage underneath.
Raised floor underneath if you need dry storage - if there is room?

[hopetown]

You need some where for the water to go.
Drainage provides an easy flow path.
Just trying to stop water is difficult & more expensive.

Drainage - around outside + drainage underneath.
Raised floor underneath if you need dry storage - if there is room?

Thanks PC. Working on it. Just looking at backstop options, just in case. But maybe should just 'overdrain' it!

Cheers mate

[Don't believe the Hype]

Yep. easier to over engineer the drainage than to waterproof for runoff caused by the drainage being inundated.

[hopetown]

Yep. easier to over engineer the drainage than to waterproof for runoff caused by the drainage being inundated.

Great, thank you.That's the way I'm heading now.

[recemember]

Hey Hopetown

Did exactly this work to our last house (now a rental). Old, shabby subsoil drainage had failed and a decent Auckland spring downpour saw water coming through the slab, into the garage, into the lower lobby and bedroom of the house. Each downpour just escalated the damage/mess as once water finds a way!

Speak to Joel at Your Local Plumber (sorry guessing you're Auckland based, not sure I read). He helped with mine. Was a $20k solution but did it in $8k with a bit (read a lot) of manual labour from me, as the area wasn't accessible by digger.

Trench right along the edge of the house (top side), drainage coil right along the back, catches it, takes it all to a silt trap then off with the stormwater off the property. No issues since!

Also did some underneath the house, same approach and that was essentially our "insurance policy". Also sealed the slab of the garage, building paper lined any walls exposed to the bank, as well as vapour barrier to keep raising damp at bay.

Hope this helps.

[Merlot Mike]

Was a $20k solution but did it in $8k with a bit (read a lot) of manual labour from me, as the area wasn't accessible by digger.

Trench right along the edge of the house (top side), drainage coil right along the back, catches it, takes it all to a silt trap then off with the stormwater off the property. No issues since!

Was the drainage coil laid at the foundation? How deep did you have to dig down? Your plumber handled the connecting of coil to stormwater I assume or can that be done by a handy person? Is the silt trap necessary?

[recemember]

The drainage coil was adjacent the slab on the lowest part of the house and probably about 400 from the foundations at the top.
Dug down 400-500, about 300 wide.
They handled the drainage coil & scoria to ensure sufficient fall as it was a long run. They connected the two to the single silt trap then that onto the stormwater. Silt trap being there to ensure no blockages over time and access to clear out, so recommended.

[MarkD]

just want to add an option that Since your house is lower than the adjacent hill- a diversion channel/swale of surface water is possible in your case provided you have some space for the swale? Obviously, water should go somewhere, as long if we can divert the flow out of the house, it might help. Would be helpful if you can have some photos to show your house situation ?

Just Google Image Grading around the house and you will see some ideas. (Couldn't attach the pictures here)
Feel free to PM me if you have questions.
Mark D
Civil Engineer specialized in Land Development