How to fix house drainage problems around homes built on sloping land.

If your house is built on a sloping site and you have drainage problems and water entering your basement garage or your basement storage area then this video is for you!
Join Matt Cornell, an experienced structural design engineer from #Australia, for a chat about:
- How to stop water from entering your #basement.
- How to improve the #drainage of your backyard.
- How to minimize water coming into your basement and causing mould.
- How to stop water from causing efflorescence on your walls and floor.
- How to drain water away from your house foundation effectively.
- Why French drains on the upslope side of your house could be causing your basement to flood.
Matt explains what he looks for when assessing drainage issues on sloping land and what you can do as a homeowner to address some of these issues yourself.
We'll talk about where the water is coming from on a sloping site and how you can cut it off and divert it before it becomes a problem.
Agg trenches and agi pipes, spoon drains, and field inlet pits (also check out this video: • How to fix house drain... ) are some of the solutions but when done badly they are also part of the problem. Check out our video and learn the difference!
If your question is "how to drain water from under house" then the answer is that you should cut the water off before it gets under your house. Find the source of the water and cut it off upstream and uphill of your house.
If you need to know "how to get rid of groundwater under the house" then watch this video on how to protect your home from bad drainage.
Leave a comment or ask a question. Everyone's house is different so sometimes the best answer is an inspection by a qualified engineer.
Chapters
0:00 Introduction
0:22 Where is the water coming from?
1:35 Does water come from upslope neighbour?
2:53 Does water come from upslope on own property?
3:14 Do your roof gutters and downpipes overflow?
4:12 Do you have sandy ground over clayey ground or underground springs?
5:24 Is there gravel backfill behind retaining walls?
6:36 Has the waterproofing on retaining wall failed?
8:02 Is there water sitting in trenches behind the retaining wall?
8:58 Are the roof downpipes connected to ag pipes and ag drains?
9:31 Summary of the drainage issues for houses on sloping sites
10:16 Introduction to solutions to solving drainage issues
10:46 How to fix water coming from an upslope neighbor
11:38 How to fix drainage problems for water landing on own property
12:25 Why field inlet pits are a bad idea
13:23 How to solve drainage problems from roof gutters
14:53 How to check downpipes discharge downstream of the house
15:48 How to use correctly use agi pipes to capture water from underground springs
18:08 How to fix gravel trenches located beside a house
19:47 Fixing retaining wall waterproofing
20:58 How to fix roof water being discharged to the agi pipe
22:24 Summary
24:35 Thank you
#cornellengineers #building #drainage #engineering #construction
For more information check out our website post on drainage for houses on sloping sites. cornellengineers.com.au/house...
Please subscribe to the Cornell Engineers channel to be notified when we upload new videos. More structural engineering explainer videos coming soon.
Other questions we answer in this video:
How do you improve drainage in a sloped yard?
How do you drain a sloping block?
How do you divert water on a slope?
How do you handle water on a slope?

[@TheRenovationProject]

Great information, thanks. You hit the nail on the head when it comes to our current issues with our property.

[@CornellEngineers]

Thank you. Glad we were able to help. Hopefully you can solve the issues at your place. Matt

[@qingluo8676]

Great job, thanks Matt. Keep it up and look forward to your new videos.

[@RobKramer]

You’re an absolute treasure. 70’s house with one corner stuck deep into a Sydney sandstone ridge. Kind of felt my way through managing drainage challenges (down pipe thru a concrete slab into the upslope dirt? Why not! (Downpipe redirected and hole concreted!!). All was working til the big rains of Feb22, so now revisiting some decisions and going harder. I was resisting more concrete, but you’ve pretty much sold me on a concrete spoon drain down the backfilled side slope. Appreciate the logic and confidence that I’m not barking up the wrong trees. One more thing, less passive, is a sump dug into the crawl space between the downstairs living area (thank goodness for that) and the rock face, with a pump that discharges groundwater down slope. Thanks again for sharing your knowledge around drainage. Really appreciate it.

[@CornellEngineers]

Hi Rob Thank you very much for the kind words. The Feb 22 event was a killer - and a lot of buildings had water entry that hadn't before. Bit of a stress test for site drainage and an opportunity to fine-tune overland flow management for some. For those waking to water running through their bedrooms, it was more like a hellish nightmare. All the best with your drainage journey. Happy we could help. Matt Cornell

[@milamf1529]

So clear and informative - sure could use your services - if only you were in Sydney!

[@pas0003]

As someone that knew absolutely nothing about drainage and plumbing, just yesterday I can now confidently say that I've got a rudimentary understanding of the domain. I can also now understand that the plumber that told us that it's okay to discharge gutter water into the ground to be picked up by the AGI pipe is a bad idea. Thank you so much!! This video is a gold mine of amazing information!!

[@CornellEngineers]

Thank you GRoss for your feedback. Very happy that we could help. Matt Cornell

[@johnmills-dg8zr]

Thanks Matt, you answered my questions on isolating the moisture problem

[@CornellEngineers]

Very glad I could help John. All the best. Matt

[@Iexecutethings]

Great video! Our scenario is slightly different in that the house is built on sandstone. Piers are on the sandstone for the first floor, but water seeps through the sandstone straight into the lower level. You can see water weeping out of the sandstone, and across the concrete floor. The other observation (in a tiled area) is rising damp from underneath the slab (which is presumably on the same sandstone)

[@waterstopsolutionsqld3200]

Great explanation, Matt.

[@CornellEngineers]

Thank you Anne-Therese 🤩

[@jonathantezbir1178]

Great video! Appreciate you sharing your knowledge! Just subscribed and liked.

[@sarmonikasandy3934]

We just found a home we wish to buy and the rain 2022 eroded a large part of the hill the Queenslander is on. Great video

[@benfoley5832]

Very informative. Thankyou.

[@CornellEngineers]

Thank you for your feedback, Ben! I'm glad we were able to help. Matt Cornell

[@mw-le1ug]

Matt, this is the best drainage video ive seen. 50s house built on a slopping block. Big sandstone shelf just below the surface. Lots of water moving on there rock shelf hence getting under the house, Unfortuanly i have to capture the water right at the house as there's sandstone boulders in the way of capturing further up. I'll defiantly get the wall waterproofed as I don't think it ever was. Id love to spoon drain it and but its about 2 metres below the and only about a 1 foot wide trench. How effective would a large ag pipe with the right fall covered in gravel? The thought I burying all my hard work with gravel scares me! Thank you

[@Ninja_Drummer]

Thanks for the informative video. I'm grateful you take the time to differentiate between the different soil types and how they impact the suitability of the solution used- this is something many people gloss over with a one size fits all approach. By the way, I found it interesting that you draw and write using almost exactly the same scrawl I use ahaha!

[@CornellEngineers]

NinjaViewer, maybe we're related?

[@nigelknight1435]

In the UK I was an accredited contractor for Sovereign Chemicals and they have a product for tanking the negative side of a retaining wall called Hey'di K11, I have turned basement areas into habitable council approved rooms using their system, once applied you need to plaster the wall with a thermal type plaster, this will make sure the dew point falls within the thickness of the wall and not on the inside surface. Sovereign have videos on KZbin about their tanking products which are worth watching, tackling the negative side of the wall on a existing building is far cheaper than trying to fix the positive side.

[@CornellEngineers]

Tacking the negative side of a retaining wall is a good option for some people - those without any bathrooms or kitchens or appliances or return walls in the way. I definitely don't discount the use of waterproofing the inside of a wall - but where do you terminate the waterproofing? What if the water then comes up through the slab on ground? What about the side walls? What about water that runs along the inside of the retaining wall and comes out around the corner? I have seen waterproofing being installed nicely to the inside of a wall and I have been asked to solve water entry for walls that have already been negatively and positively waterproofed. At all times, reducing the amount of water near the retaining wall is a helpful thing. When that can't be done (water table or unable to solve external water issue) then we have negative side waterproofing as a backup option.

[@parsecscopeking2580]

Good logic

[@CornellEngineers]

Thank you. It is pretty logical, isn't it? Yet so many people get it wrong and have trouble keeping water out of their houses. Thanks for the comment! Matt Cornell

[@alexandalycepiazza4562]

Great video.

[@CornellEngineers]

Thanks for commenting. Glad you liked it.

[@alexandalycepiazza4562]

Sent you a PM on your Instagram page

[@sdjnwhyNZ]

If it's this serious for an inland scenario, it may be worse for a coastal house since everything in the air is salty.

[@CornellEngineers]

Possibly - but I think the issues are different. Corrosion and drainage are both significant issues that need to be addressed in new and old homes. Salt air and salt water are a problem for exposed steelwork - even for lightly galvanised steel. Whereas salt in the ground water won't be any worse as far as site drainage is concerned. Thanks for commenting and I hope yu enjoyed our videos! Matt Cornell

[@alexc5369]

Thanks Matt, I wish I found you a bit sooner, I've started to dig a trench around 2 sides of my house for an ag drain, but I'm not 100% confident it is the solution. The lawn extremely saturated for days after a rain.. when you walk on the lawn you can hear the squelching through the grass and water comes up between the toes... After the last rain I dug a couple of investigative holes about 300-400mm deep, they were filling up with water, I would empty a couple hours again would fill up, multiple times over a couple of days. I am in Brisbane, I would love to organise someone to come have a look and assess before I go any further to give me some insight. Where abouts are you based? Thank you! Alex

[@tillyhart2669]

I found this video when I was looking for some help with a huge water problem in the basement of my house on a sloping block - it's a nightmare - was going to get the french drains looked at but after watching your vid I'm not so sure. I'd love to consult with an engineer but am in Tassie and have not idea who to contact. Can you suggest the best way of getting a reputable engineer (is there a licensing organisation for example that I can go to for recommendations?) to visit my block. Wish you were inTassie!

[@brucef]

Hey Matt, thanks for the video on all the different sources. Very useful. I've been sorting out problems with my 1950's besser block house, it's had high humidity (like 90+ occasionally in the worst room, much higher than outside in Sydney). There's a lot of moisture in the soil in the sub-floor (I think little mineral stalagmites are an indication it's been a long standing problem?). Concrete paths/driveways on all sides, sloping section, bit of a lawn out the front. It's unclear where the water is coming from, other than it's near the front (where the lawn is, also we're 2m down from street level), but there's not a lot of lawn. Below the lawn there is sandstone about 60cm down, possibly continuous under the whole property. How can I prove it's coming from the lawn area? I could dig a hole but not sure if that'd be useful. Could it come under the driveway from the uphill neighbours in the same way? In the meantime I've mitigated most of it by fitting two Expella extraction fans in the vents, and I'm now getting indications of drying everywhere (and the rooms spike to 75% occasionally, falling to 40% sometimes and averaging in the 50s, rather than the 80s). This appears to have been a problem since it was built (successive owners have fitted 3x more vents, whirlybirds(!), and left the access door open (it was rotted off)). I'd prefer to fix it rather than mitigate it though.

[@CornellEngineers]

Hi Bruce A hand-dug hole on the upstream side might be worthwhile. It will tell you the nature of the soil, the depth to the rock and, if you leave the hole open for a little while (and maybe covered for safety), if water ponds in the bottom it may indicate that a gravel-filled trench will capture some of that water. Your issue will be getting water to track sideways along a gravel trench when it could just as easily continue flowing down through the sand towards the house. We've used good, powered ventilation systems before where there was an overwhelming source of water )really high water tables) to prevent moisture from coming up through the floor. I've heard of ventilation systems being controlled by humidity sensors to ensure the system only runs when the relative humidity sub-floor is higher than the external air humidity.

[@honkythebastard4746]

I get the neighborhoods water and my idiot neighbors put a french drain in that is suppose to empty out in the street. They don't believe in gravity and think that it will run the water up a 4% grade in the last couple feet. So it dumps on my driveway and my driveway sinks in toward my foundation, flooding into my garage and it has broken the inner 1/3 of the driveway, tilting it in such a fashion where I pools along the driveway and into my cement walkway then once it's deep enough it floods on my grass making my yard a swampland. My soil is red clay and sand so it hangs out.

[@CornellEngineers]

Wow HTB Water coming from neighbours is a common complaint. Each person has to do what is right for their place without causing nuisance water to downstream neighbours. I hope you can solve your drainage issues and manage to capture it and divert it safely around your place. Best of luck Matt Cornell

[@hannesRSA]

Nice video. I watched this for some ideas - but essentially my main problem is that I get overland flow from 2 neighbours, and we are all below street level. I've got 2x100mm storm water pipe connections at least, so can get rid of some of it. Would need more connections for all of it... Assuming the 375mm pipe can carry more.

[@CornellEngineers]

Thanks for the feedback. Glad you liked it. The bigger the pipe the lower the friction losses and the bigger the cross-sectional area so yes a bigger pipe can carry more water. (www.expresssewer.com/blog/how-does-water-pressure-flow-work) But I guess the point of my video is, "Can you address the stormwater issue by collecting and moving the water with other above-ground water-carrying options (spoon drains, swales, bund walls) rather than pipes and trenches and ag pipes?" If pipes are the only option then you have to do a good job of ensuring the pipes are correctly sized and that there is a backup overflow pathway for the water if the pipes block up. Best of luck solving your particular problem. Matt Cornell

[@hannesRSA]

@@CornellEngineers yes thank you, it's definitely useful to know what options are available - currently our house has a trench on one side only, so some more spoon drains etc will be needed for the periods where rain peaks. And the pipe discharges is to avoid dumping so much onto my poor neighbour.

[@CornellEngineers]

@@hannesRSA It's very considerate of you to be considering the effect on your neighbours. There should be more people like you.

[@calluma8472]

Excellent video - I have only one question. Do you have any recommendations on how to find a decent company to do the investigative work and repair for these kinds of problems? There are a lot of folks who will come round and jump straight to a french-drain solution without doing the analysis you are talking about. (obviously I am not in Brisbane otherwise I'd be phoning Cornell)

[@CornellEngineers]

Thank you very much for your kind words. You could always ring and ask if they have watched my video? Kidding. But lol. Really. It is hard to find someone that knows about buildings, drainage, soil, slopes, waterproofing, and stormwater design. Look for someone old (aka experienced), respected (aka positive reviews) when you Google drainage engineer. Steer towards a structural engineer with drainage experience more so than a subdivision engineer with structural experience. Best of luck. I hope you find a solution to your drainage problems. Matt Cornell

[@sanctuaryplace]

wonderful, want to come fix ours? are you in south coast nsw?

[@CornellEngineers]

Hi Julie. Sadly, no. We're Brisbane based. Which isn't to say we don't get around. South coast NSW sounds lovely but a little bit more than a day trip from Brisbane. Drop me a message from our website and I might be able to put you in touch with someone that we know and trust. cornellengineers.com.au/contact-us/ Matt Cornell

[@PanamaSticks]

Sir: My family has had a 35 year battle with water seeping into the basement, soaking the block walls, causing efflorescense, soaking and cracking the basement and garage floors. My late parents got bad advice, and worse contractor work. No one in this area seems to know what they're doing except to trench the basement floor and run sump pumps. And then the problem is where to run the water, when there's nowhere to run it to. And what happens when the powee goes out? I am 69 years old and in poor health. I can no longer lug buckets of water up the stairs and throw them into the street. I hired an engineer last year, but he didn't have any good ideas, and wouldn't manage the project ir even write up a report. You seem to understand this stuff. I don't. Can I hire you, and can you find and wirk with a local contractor to get it solved? How do I contact your firm?

[@CornellEngineers]

A story we hear all too often. We might be able to help if the property is in Queensland. Head to our website and send us your details cornellengineers.com.au/contact-us/ If you're further afield it gets more difficult. Let's start with where you are and we can go from there. Matt Cornell

[@josevargas4160]

Hi Matt, I have the same issue but at the front yard of the house (the soil is mainly clay). I bought this house no long :/ what can I do to fix the drainage? Thanks

[@CornellEngineers]

Hi Jose That's a very good question. Once you have understood the issues of where the water is coming from, then the next step is to try to find ways to divert the water around your house. You could try getting quotes from a landscape gardener (once they have watched this video). Each and every house is different. The soil conditions are different. The slopes and the existing services are different. So all of these aspects need to be considered when you formulate your master plan for site drainage improvements. Best of luck improving your drainage! Matt Cornell

[@josevargas4160]

@@CornellEngineers Thank you :)

[@RobbieFitzAu]

Wish I asked you guys first. What if your house has all of those factors combined?

[@RobbieFitzAu]

Minus the roof drain going into an ag pipe. That’s messed.

[@kk99990000]

We just moved into a 4 year old house(reactive soil in melbourne, on waffle pod slab). In march, dug a post hole next to the wall in backyard. It keeps filling up with water which is coming from underneath house/slab. It was initially filling up at the rate of 1 litre/3 minutes but never overflowed. We started emptying it with the pump and eventually it slowed down but never completely stopped. Had couple of days rain and now it is filling up faster than before but still doesn't fill up to ground level. Except the front, all sides of the house have weed cloth with garden rocks on it. Soil grading on one side looks pretty flat. We initially though it was a leak in water supply but after the recent rain, it seems it is rain water which is getting under the house somehow. What can we do to resolve? kzbin.infoSpAxSMKo_Js?feature=share