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Comment by refibrillator | Hacker News Reader

I’ve built quite a few french drains in residential settings, some lasting longer than others - I’ll share a few hard earned lessons here:

Soil migration is the number one failure mode. This is mentioned but perhaps a bit understated in the video.

To prevent soil migration you absolutely need commercial grade geotextile fabric wrapping the gravel and pipe.

You can buy pipe with much bigger and more numerous holes than the tiny slits depicted in the video. That also obviates the need to decide what orientation the holes should be.

Void space is the most critical factor when choosing gravel. You need a lot of space between the rocks to support fast drainage. Do not use playground pebbles or anything similar. Pay close attention to the type of aggregate you’re buying.

Calculate how much water you actually need to drain. You can use the “100 year flood” values for your locale to get an upper bound on rainfall, then multiple by drainage area. This is especially important if your roof is part of the watershed.

https://www.usgs.gov/special-topics/water-science-school/sci...

Sometimes there is insufficient gradient to move the water anywhere, ie the land is too flat. In this case you may be better off building a drywell, which is constructed very similarly.

https://en.m.wikipedia.org/wiki/Dry_well

View on HN

Our first house was one a 1/2ac lot at the end (bottom -- this will become important later) of a cul-de-sac in a great semi-urban neighborhood in Cary, NC. We learned after repeated backyard flooding and near-incursion of storm water into our patio door that our street had been built on what had been the original stormwater collection pond for the larger neighborhood. The builder got permission from the city to move the pond to build our cul-de-sac, but that didn't stop our street from still being the lowest point in the neighborhood, where all surface water ran-off to, and our house was at the very lowest point.

Long story short, we ended up installing a french drain on two sides of our house, putting a drain at the end of our driveway to redirect water [from just running down our driveway to our house], having the front wall foundation rebuilt and jacked up because the footer had nearly completely eroded (1970s house), and still needed to add two 24" square drain boxes in the back yard (with buried 4" PVC draining into the creek at the back of the property) to remediate all this. It was also a tree-filled lot and the drain boxes would almost immediately clog with leaves during heavy rains, so I spent a lot of time out there in ankle to knee deep water with a rake to keep the drains clear.

This still wasn't enough! We got a so much surface run-off from our uphill neighbors that it looked like a sheet of rushing water across our backyard during heavy storms. We had a creek at the back of the property but were not allowed to mess with it because of Corps of Engineers easement regulations. At the end of the day, we finally solved our problems by getting an agreement from our neighbor to let us dig a surface water drain from the low point in their yard into the creek, and then we'd build a "temporary" (cf prior easement rules against permanent walls) berm along the property line to prevent surface water from coming into our yard at all. That "berm" was 76 bags of Qwikrete stacked three high and covered with grass clippings, yard waste & mulch. Technically we could have removed it if the city had inspected, but it was very much a cement wall.

We have never since, and never will, build or purchase a house at the bottom of a hill.

One of the prior houses I lived at had so much flooding and water leakage problems from poor construction (prior additions that weren't strictly legal) that lead to carpet and padding having to be removed from concrete floored rooms and eventually mold problems, that when I bought a house a few years after we'd ran away from that disaster of a house we made absolutely sure to my at the high point of the (new) neighborhood so we weren't in the drainage path for anyone.

It's particularly demoralizing to see the scope of the problem when it's all that water flooding your property and know there's nothing you can do in the short term, and even the long term is just trying different things and hoping they work, knowing that it will probably take a few tries.

Flooding can come in many forms.

Perhaps the balcony over your front door is not properly constructed and is not properly shedding rain, so one day during a torrential thunderstorm you suddenly have a flood coming in OVER your front door.

Perhaps your water heater pan is not draining correctly, and one day you have a catastrophic containment failure in your water heater, causing an interior flood.

Perhaps you change the toilet in an upstairs bathroom, and the new modern toilet is not providing enough water per flush to make the long run of the upstairs plumbing. So, it clogs up over time, then one day it backs up while you’re taking a shower, and you’re standing in multiple inches of grey water. Then the water does slowly drain, but you don’t notice that the pipe has cracked above the clog and it’s actually flooding into the room below, through the light fixture.

Perhaps the main schedule 40 PVC pipe from the water main at the street slowly develops a crack, due to the roots of a tree nearby, and one day you discover that the water pressure in your house is really low and that you have flooded the whole street.

Guess which of these have happened to us?

All of them?

Correct in one!

Mine were incorrect drainage outside, causing water to pool high enough inthe back yard that it came through the slider into the converted garage, soaking the pad and carpet there (in a few different locations actually), and the much worse one where a room was build off the same garage onto a concrete pad that was laid, but one of the walls was build on top of a covered deck that was build off the garage on one side, which had water run down it, hid the deck, then immediately go under the wall to the concrete pad meaning even moderate rains that didn't result in outside flooding would result in that room's pad and carpet getting wet and needing to be entirely removed, and the wall ripped out and rebuilt as it eventually was overtaken by mold. A large chunk of the house needed to be blocked off, industrial fans installed to dry it out, and then professionally redone.

Building codes exist for reasons. Sometimes they seem frivolous, but often they're there for a damn good reason.

This sounds like a nightmare

I've ruled out several properties in my current homebuying search for this exact reason. Having lived next to the neighborhood collection pond once before (a rental thankfully), I'm extra paranoid about stormwater and drainage now.

I've seen a number of homes in my area where the builder received special permission to build right where the drainage needs to go. Some were beautiful and I was tempted to give it a shot, but your story reminds me that I need to trust my gut on this issue and head for high ground.

House in shallow valley. Basically bottom of 3 hills. Multiple floods yearly. Basement pretty trashed.

Beat it with 2 ditches, a drain, a berm and 2 pumps.

I live at the bottom of a valley, but luckily in a tiny house on a concrete pad, so I have no basement and I'm raised up two feet off the ground. That works pretty well for the house, but the driveway and yard still floods. So I dug a "pond" and small ditch things to channel water to it. You can't really tell where it is because I let my yard grow wild, but when it rains hard the water fills it up, and it evaporates/drains naturally over a couple days.

The ditch actually speeds up the water drainage. I dug the ditches to divert the water around the property line, so the surface area of ditch in total is large, even though you can't really see it and it doesn't get in the way. I figure at least a quarter of the water drains through the ditch before it gets to the pond. This is probably helped by the fact that the soil is very rocky.

I'm going to say that the vast majority of homeowners are not paranoid enough when it comes to buying their home. It is a huge investment and comes with very high transaction costs yet most people seem to make the decision based solely on superficial aesthetics.

What would you recommend noobs do, when buying a house? I guess hiring an expert would be the recommended approach, but all “experts” I have seen were all almost as superficial as I was - one literally assessed the wrong house. I’d pay good money for a good one, but it’s hard to find.

Find an aggressive home inspector that isn't associated with your realtor, preferably one with general contractor experience and someone who is older. Like it or not, older folks have seen more things go wrong in more ways and can spot problems that younger folks might not be familiar with.

I have certification of an inspector with various home things… Flooring, roofing, general home inspection.. no one wants to pay what it’s worth so I don’t practice that, it’s just fun for learning about the building trades

Further - if you never have a problem the value of the inspection is zero. If you do have a problem the value of an inspection after the problem has occurred is minimal. The value of an inspection that prevents a problem is something - but how to quantify that is difficult.

You quantify it using a binomial. Then calculated the weight averaged expense repair cost using that binomial.

Depending where you live local/state/fed government will keep maps.

Topographic maps, flood risk maps, wildfire risk maps, maps of services nearby (substations, transformer locations, storm drains etc), easements, special planning/protection zones, surrounding area zoning etc.

These should all inform your decision. I've vetoed houses because they back onto nature/wildlife reserves, are too near substations, are in flood risk areas etc

>I've vetoed houses because they back onto nature/wildlife reserves

Why is this a bad thing? To a naive person, it might seem like a good thing, because you get to look out into a forest rather than someone else's yard.

I should have anticipated that question!

Essentially because nobody was allowed to trim/maintain the trees due to it being a natural habitat. It's nice to look at but when a 60m tree falls in a storm and wipes out your house it's not great. The reserve was also on the north side of the property and down here in the southern hemisphere that means that every year as the trees grow your house gets more and more shade with accompanying maintenance issues.

I should add that people may weigh that up and be happy to live there, but people should be aware of the risk/benefits before they buy. Natural light/property orientation and shading is a major issue that most people forget about.

I had a structural engineer come and look at a house I was thinking of buying. It cost me $500. I didn't buy the house, and that $500 was some of the best money I've spent.

How did you find such an engineer with the applicable expertise?

The same way you hire a company for any service, start by searching for local structural/construction engineering firms and then call a few and ask if they’ll do an inspection on a residence.

If you personally know any architects or general contractors in the residential market, they should be able to recommend someone.

Selling a house in Denmark requires the seller to acquire a “condition report” from a certified inspector. The report is valid for 6 months and costs around $1000. This also ties into the optional “owner transfer insurance” which covers serious defects / building code violations undetectable by the inspectors. The insurance lasts 5 years and costs $2000-$5000

In the US afaict inspections are a plus but not required for sellers to provide. Lots of people were waiving their right to inspection in order to make their offers on houses more attractive to buyers. Kind of a stupid thing to do, but people had low interest rates and were desperate to buy

What did they find that was so bad?

1895 house in Oakland with a soft story condition and a dining room that was cantilevered out over the aisle. It was listed for something like $850k in around 2018, so kind of cheap! But correcting the soft story and the rest of the framing would have been astronomically expensive. He guessed something like 400-500k, and now having experienced home renovations, I am fairly certain he was in the ballpark.

Shout out to FEMA's FIRM/FIRMette maps:

https://msc.fema.gov/portal/home

Here in Western Australia there are online floodplain maps which show the extent of a 100-year event. Very usful when you see somewhere nice but wonder why the house and outbuildings are all crammed in the front quarter of the plot...

get a Chinese feng-shui expert; cheaper than pros and reap benefit of thousands of years of real estate wisdom. /s but not really /s lol there are some methods in it's vast amount of madness

Generally speaking, if inspectors did their jobs well, almost nobody would ever buy a house, due to the prevalence of existing issues and the cost of remediation. I've found that there is a duality of thought among homebuyers, where most want a "perfect" condition house, but also don't want to pay for a perfect condition house. At the same time, home sellers also don't want to pay any more than they absolutely must in order to sell the house, so you end up with inspectors as these not-entirely-impartial middle-men whose job is mostly to CYA while not identifying too many problems that could create a reputation for them that might limit future realtors & home sellers from using them.

It's all pretty silly, really, especially considering the hottest markets, where you either want a house or you don't, and if you you'll probably pay top dollar with no contingencies and possibly not even your own inspection... since the seller knows if you don't buy it someone else is in line right behind you. Most of the time, houses sold this way aren't in significantly worse shape than those that are fully inspected and repairs made before the transaction.

Overall, this has led me to believe that, in most cases, pre-sale inspections don't really benefit anyone, especially since it's so difficult for buyers to seek E&O recourse/damages against either an inspector or seller after the sale closes.

I think it depends on who is paying the inspector. When we bought our house, the realtor we were working with connected us with her best and most rigorous inspector. He found fifty pages worth of stuff that was wrong, but most of them were fairly minor.

We took that list back to the sellers (who were then legally required to provide a copy of that report to other future buyers), and we simply waived the little stuff. We wanted them to fix the big stuff. They didn’t want to do that, so they came down on the price by a considerable amount. He saved us tens of thousands of dollars.

Now, given the problems we’ve had since then which the inspector didn’t identify, we would have paid back more than what he saved us — Except for insurance coverage. USAA is really good about paying out on claims, when many other insurance companies would weasel out.

We love this house, we love this neighborhood. If we had to do it over again, I think we would have pressed harder to get even the minor problems fixed or to get the seller to come down even further on price. But I think we probably would have still bought this house.

I don’t blame the inspector for anything he missed. Most of those problems were well disguised, until such time as there was an actual catastrophic failure. He couldn’t have known. If I knew his name and contact details, I would recommend him to future buyers in the Austin area.

And we’re definitely sticking with USAA.

20+ years ago, I had moved into a newly built home. And the first serious rain we got, I had water come into the living room (flooded the porch and seeped under the door). There was no insurance coverage since it was "surface water" and thus excluded. So I had to use a shop-vac and rent a couple of blowers to dry it out.

There was a ditch out back but it obviously wasn't deep enough. I did the math and ended up with an astounding amount of water flowing by (something like 20,000 gallons per minute[0]) and complained to the builder about it. They sent a couple of guys out there who installed two 4" corrugated drainage pipes and said it was good enough.

When the next big rain happened, where those pipes emptied out there was a 3 foot tall fountain of water from the pressure. It was an amateur Bellagio, lol. The yard still flooded but luckily didn't come into the house again.

Since then, the landscaping came in throughout the neighborhood which controlled the runoff. But it taught me a lot of respect for getting slopes & drains right - Always use a larger pipe than you think you'll need.

[0] The formula seems to be: V = 0.408 × Q/(D^2) where V is velocity in feet-per-second, Q is the flow rate in gallons-per-minute, and D is the diameter of the pipe in inches. I estimated the diameter based on the land profile that was underwater, and timed the velocity by following twigs/leaves floating by.

You probably got a bit higher number than the true one, because water flows faster the farther it is from the floor/wall, and leaves float so they move like the fastest water, not the average water.

This is called “overland water” and “overland water coverage” in insurance speak. It is usually not even offered as additional coverage.

I've visited Lloyd's Building on a building tour once, and seeing the scale and sheer floors of actuaries with PhDs in god knows what domain made me a firm believer in the real life prowess of the insurance industry. I honestly don't think consumer insurance is worthwhile, but commercial definitely if you have an equally capable team of actuaries to run the numbers and they stack up to cover the risks involved.

Sure but all these people are there to ensure the insurance will get ahead, not to help the customers.

One of my friend works in reinsurance and his favourite joke is that every time the insurance company pays a claim, someone is getting fired. Obviously a joke but it seems to paint a fairly accurate picture of how the business is run.

As I understand, a lot of property and casualty insurance companies are structed as "mutuals" (not sure the exact term). And, most of the annual profit is refunded to customers. They are basically run as non-profits.

Technically true, but the people in charge are not the customers. The people in charge(C-Suite) have zero incentive to ever refund any annual profit. They have all the incentives in the world to ensure their compensation just happens to suck up any and all annual profits. Who is going to stop them?

Vanguard(the brokerage) is structured the same way pretty much, except it's the various mutual funds(like VTSAX/VTI) that own the larger corporation. So far the infection of c-suite salaries continually growing larger and larger hasn't gotten to Vanguard yet, but they are now a few CEO's removed from the original founder(Jack Bogle), so it's probably about time that shift starts to happen.

    > The people in charge(C-Suite) have zero incentive to ever refund any annual profit.

This makes no sense. Well run mutuals regularly refund part of insurance premiums each year.

For example, in 2020:

    > USAA, the country’s fifth largest property-casualty insurer, will be returning $520 million to its members.

Ref: https://newsroom.usaa360.com/news/usaa-to-return-usd-520-mil...

If what you say is true, why did they return any money at all? They could easily pay that to C-suite and senior execs in huge bonuses.

Also, to clarify, the correct term is "mutual insurance", which Wiki describes as:

    > A mutual insurance company is an insurance company owned entirely by its policyholders. It is a form of consumers' co-operative. Any profits earned by a mutual insurance company are either retained within the company or rebated to policyholders in the form of dividend distributions or reduced future premiums.

Ref: https://en.wikipedia.org/wiki/Mutual_insurance

A lot of insurance companies have caps on profit, either as part of their structure or by regulation. Often the cap is structured as a percentage above covered losses, so administrative costs, including executive salary expense are effectively limited. In health insurance, this can lead to cost inflation, but I haven't really seen that in home and auto --- the market of service providers is so different.

Certainly, they're in business to make money, and helping customers is just part of the process, not their goal.

But --- it's in the customers' interest for the company to be accurate about accepting and denying claims. If the company accepts claims that should be denied, that means higher premiums. If the company denies claims that should have been paid, that may result in the company having to pay those claims after appeal/lawsuit and possibly with penalties; penalties get paid by the pooled insureds one way or another.

Insurance fills a need and is not just an evil company doing evil. Most insurance covers risks of loss that the insured would be unable or unwilling or at least unhappy to cover themselves. For most homeowners, if their house burns down, they would be unable to rebuild without insurance, unless there was clear liability from a person or company with big pockets.

    > I honestly don't think consumer insurance is worthwhile

So no fire insurance on your house?

From what I've observed, if the insurance company uses a mascot of any kind, you will have difficulties in getting them to pay a claim.

This is consumer insurance, so your typical auto, home, renter's, etc. policies. If you need commercial or E&O coverage, ask your broker to check them against the AM Best rating list.

I checked my policy and they use the "surface water" term. So it's probably something that varies by company and perhaps region.

To get a flood policy you would have to speak to a broker about whether you qualify for the National Flood Insurance Program. They won't issue a policy to you directly.

Sorry to hear of your troubles. We live in Holly Springs, NC not far from Cary. When our builder was showing us land/lots that were available at the time they only had lots that had driveways that would pitch towards the homes (in other words the road was higher than the house, not by much maybe 2-3 feet or so.) Of course developers and realtors always assure you it won’t be a problem - I was not reassured and so we passed on these lots. A few months later a lot became available that was well above street level. We’ve been here 10 years and never had an issue through heavy rains and even a couple of hurricanes. But we’ve met the neighbors who bought those properties with the driveway pitching towards their homes and they complain about having water coming into their garages whenever we get heavy downpours. If you’re going to live somewhere long enough that may experience heavy rainfall, it’s best to be well above the low end of the neighborhood/street.

And this is why if you own a very old house, you will notice is up on a hill

That isn’t my experience. We own a 15th C house which was originally a coaching inn beside the main road, which ran along the bottom of a hill.

I have almost exactly the inverse situation. We are at the end of a cul de sac that is capable of efficiently draining water away and out of the neighborhood. But in roughly the spot where your drainage creek is, there's a large strip mall parking lot (across the street from our backyard). We don't get a lot of rain in annual total, but when it does rain heavily a flash flood comes into our backyard and must cross our side/front yard to drain into the cul de sac.

The previous homeowner put in a DIY french drain, but either he didn't do it right, or it's too flat, or it's too small, or it is clogged. We instead get surface water flow and erosion along the same path where the french drain runs.

(It doesn't help that when our neighbors got sand delivered for an above ground pool bed, the delivery truck dumped the entire pile of sand ON TOP OF the river rock exit basin for our french drain. The sand was later removed/used but I was still upset; unfortunately it was my brother in law who ordered the sand. Since the drain is above it I don't think it went in the drain, but maybe this rock basin was supposed to be a dry well.)

I am thinking of building something like your concrete berm along my back fence line, possibly modifying the french drain to just transfer the water from the far side of the berm to the exit over the cul de sac rather than trying to absorb it from the ground.

Sand above the french drain isn't the end of the world, in fact some people prefer it.

Too late to edit, but I realize I should have shared photos/videos for full effect: https://photos.app.goo.gl/kUmuhyNVXCXdTLH67

What nightmare. Sorry that happened to you.

Not sure you watched the whole video, he shows how soil migration causes failure (7:30), links to another video that covers that in-depth and discusses how geotextile isn't enough for things like damns (10:15). He also mentions that you can get pipe with holes all the way around (5:58).

Definitely didn't watch the video. He also mentions hole direction and problems, as if the video didn't go at length into the topic.

I definitely watched it but missed a couple of those sentences so thanks for the timestamps above.

Yes he does name soil migration as the biggest problem with subsurface drains, but to be fair the video is contextualized around dams.

The spirit of my comment was intended to be helpful for folks attempting this stuff at home, not to suggest a lack of good info in the video.

Ah, ok, no worries. Apologies, I should have given you the benefit of the doubt. Your comment was generally insightful.

> You can use the “100 year flood” values for your locale to get an upper bound on rainfall

I wonder, does climate change also affect those calculations, with the need to adjust those bounds upwards? I remember the (technical) term "100 year flood" getting lots of ridicule in the last years because we already got multiple "100 year floods" in the range of a decade.

Faster than climate change is development. The addition of impermeable surfaces like parking lots and buildings upstream causes more water to get to you.

Development happens faster than the flood maps get redrawn.

I wonder how well USA state agencies are doing in their efforts to map sea level rise, flooding, etc. and if they take into account development. I know a lot of work is being done in Virginia to address sea level rise, flooding in poor areas, etc. But because I live in a rural part of the state, I can't assess for development since it's not ubiquitous.

Short answer yes, but as another comment suggested, development changes adding hard surfaces in new places in the neighborhood also rapidly change those calcs.

If it was me I'd chop a zero off those N-year estimates.

But that got me thinking, how often do they adjust these estimates? Was a "100 year flood" in 1950 less than in 2000, say?

Obviously it'll be different for different areas, especially between countries, but still.

FWIW "100 year flood" refers to the flooding that is expected to occur in that specific area on average once every hundred years, not an event that will happen only once over the whole country once per hundred years. So regardless of climate change it makes a lot of sense to be seeing many hundred year floods since mass media has us caring about many areas in parallel, not just the specific area we live.

Ah, I wasn't aware of that definition. That makes a lot more sense, actually.

Also, as people have a life expectancy in the order of 100 years (75 perhaps?), there is a pretty good chance you will experience a 1:100 year event at some point in your life. Also a lot of infrastructure is built for 50-100 year life (or is still used after 100 years, even though it was designed for less).

The 1:100 year safety level should thus be considered a bare minimum for high impact events. In the Netherlands water infrastructure is designed to withstand the 1:10.000 year storm for catastrophic events, and e.g. 1:1.000 year storm for high impact events.

But even with higher safety standards, it is key to design not only for the current climate, but for the future climate over the design life of whatever you are building. Extrapolating 1:10.000 year events from 30 years of observations might seem sketchy already, but with all the uncertainties in climate change predictions is a bit of a stretch.

There's a pretty good chance you'll experience any given 1:100 year event. You're basically guaranteed to experience quite a lot of 1:100 year events, since there are so many options.

This is a misleading definition as it makes people believe that if there is a 100-year flood this year, that equal or worse flooding will not happen next year.

Long term observed water levels are fed into a model with normal distribution, and a 100-year flood is then defined as 99-th percentile of the model. This means that there's a 1% chance of a 100-year flooding each year.

Global warming and climate change have an effect that there's a lot more water vapour in air. Same air mass can deliver more rainfall on a given territory, pushing observed water levels into higher extremes, meaning what used to be 100-year flood is now 25 (4% yearly chance), 10 (10% yearly chance) or even 5-year (20% yearly chance) flood.

Yeah, that is another issue with the way the media frames things and commonly invokes "100 year flood". In my comment, "on average" is doing a lot of work for those not decently versed in probability.

https://www.usgs.gov/special-topics/water-science-school/sci...

the 100 year flood is basically a mathematical concept - its about the long term average recurrence interval - the probability that the given event will be equaled or exceeded in a given year. The "100 year flood" has a 1% probability to happen in a given year, based on historical data and a normal probability distribution (which is what we see in nature).

First time I've see someone describe this correctly.

I have to admit I have a degree in structural engineering and bashed my head trying to understand various bits hydrology for some time some years ago, and still occasionally dabble in it when I'm required to (although I leave it up to more competent hydrology experts 99% of the time).

Depending on how deep it is a drywell can be an EPA regulated thing in the US. This is because it can be a bad idea to sink surface water directly into the aquifer - naturally it would be filtered by the overlying soils, if it goes in directly then any surface contamination is washed directly into a reserve of drinking water. But, I'm far from an expert so I can't give any advice as to when one would need registration etc.

The video also mentions that sometimes the geo textile fabric is not enough since it too can get clogged, though this seems important in dams and not so in simpler projects

If you live in a place with a lot of clay, geotextile fabric can certainly be problematic for simple residential settings.

The drain pipe is at the bottom of the drainage excavation. On top of the pipe is 3/4 aggragate, and on top of the aggregate is geotextile. Soil is filled in over the geotextile. There is no clogging risk in this design. Any soil particles that make their way to the pipe are carried away.

Fine clay and silt clogs the geotextile.

A proper drain requires extensive soil testing for particle size. Video goes over this along with the issues of geotextiles.

Yeah, I saw that video and many others long before it was posted here. I stand by my comment, which is based on experience and reviewing the work of professional drainage installers on YouTube.

No one is doing soil tests for these unless they are installing huge critical commercial infrastructure.

Any advice for homeowners living in a high water table area besides "move"?

We were a bit naive buying our new construction home. It's the only home on the street with a basement due to the high water table. One year after purchasing, Hurricane Ida hit and we had water up to the door handles in our basement. Our primary sump pump runs constantly for 18 minutes then off for 18 minutes 24/7. We have a backup pump on the other side of the basement connected via the perimeter drain, and a liberty water backup pump. The only addition since Ida is a whole house generator and superior window wells.

During Ida, the street was flooded, the drainage systems were backed up, and there was no where to pump the water to.

Unfortunately, you can't "drain" into saturated soil. At that point you're building a boat more than a house: keeping water out on all sides.

I'm assuming it's a fully-enclosed basement? I.e. no walk-out side?

The best you can likely do is waterproofing the basement walls + pumping out from inside or an inside-perimeter drain. But that's only racing pump_out_flow > seep_in_flow.

And that's a bad game to be in, because water under pressure (which it will be a story below ground) finds a way.

I'd make the basement flood tolerant (limit mold-hosting materials and places water can be trapped) + pump it out quickly after it floods + buy a dehumidifier, and accept it's going to happen.

As far as I can tell inside waterproofing is a bad idea, it leaves your foundation soaking wet, excess humidity indoors, and as you point out it doesn't alleviate the pressure from outside. Waterproofing the exterior, french drains deeper than the footings (all sides), and sump pumps... That should keep things dry but it's quite a process.

Foundations being wet aren't a huge deal. Exterior is recommended over interior because it's easier to ensure no gaps. But it does involve substantial excavation.

French drains around the perimeter help, but you're literally fighting water from all directions... including directly underneath.

Have a perimeter French drain but a crack in the slab? Enjoy watching water bubble up from that crack once things get saturated.

Yeah it's not a cheap approach but unless the water is coming in really fast it'll get the basement really dry. Key to have the drain and pump well below the footings otherwise yes the water will just be under the slab.

The issue with drain/pump solution is that at that point you're doing hydrological engineering.

There isn't a "perimeter" per se, because water is literally coming from depth (in most locals / soil types).

So drain/pump just creates drier 3d soil areas. Whether that's enough to attract all the surrounding water (at a high enough rate) that would otherwise be infiltrating depends on soil permeability (e.g. sandy or clay?).

A lot of the "handyman"-type "dry basement" shops have no idea about any of this, toss a generic solution in there, and then blame the gods if it doesn't work (and they've billed for time-consuming and expensive excavation).

Ah true. I live in a hilly region so the water issues tend to be rain water moving down hill (which is really mostly laterally). In that situation the exterior drain solution works well, totally dry basement. I don't know how common it is for water in a populated area to be coming from directly below but in that situation maybe it's a good place not to have a basement.

Yup we have a dehumidifier running constantly that drains into the sump pit. The basement still has a basement smell even though it's all brand new drywall, fresh paint, etc. The dehumidifier keeps the humidity around 40%, otherwise it would be approaching 75-80%

Do you know if there's an impermeable barrier on the interior walls? And what foundation material behind the drywall?

It gets dicey applying internal barriers, because one needs to be thoughtful about making sure there's a place for water to go when it's actually too much (you don't want an internal barrier to be a dam holding back all the pressure), but it can be an option.

They sell them in membrane form or paint-type form.

Up here in Alaska, I tend to get a little water seeping into my basement at the cove joint (walls are ICF) after heavy rain and/or the spring thaw. Now, the floor in the basement is concrete, and whoever built the house had the baseboards and drywall over an inch off the floor, so towels and a de-humidifier tend to dry it out and nothing gets ruined since we learned to keep things off the floor. Trying to think of a way to address it without digging around the foundation to put in more/better drainage. Maybe just add a sump pump... I know, kind of a band-aid solution.

Are you in the construction or related business? I've had to learn some of these things the hard way myself. I learned I was outclassed and so I hired a geotechnical engineer to design my now-deployed drainage. (french drain plus site drainage)

I wonder what building codes require, ie from engineering and inspection POV, like can the things you mention even be built today? If so isn't this a failure of the planning departments?

> like can the things you mention even be built today?

Yes definitely, just depends on area and your local geology / codes.

> To prevent soil migration you absolutely need commercial grade geotextile fabric wrapping the gravel and pipe.

The article seems to be quite clear that, for critical applications, one should not use geotextile fabric at all — instead one should use (appropriately selected!) sand.

>Calculate how much water you actually need to drain. You can use the “100 year flood” values for your locale to get an upper bound on rainfall, then multiple by drainage area

How do you incorporate this into a drain design?

https://web.archive.org/web/20240807170330/https://www.ndspr...

https://web.archive.org/web/20240807170407/https://urban-wat...

Both of these links include a dry well - if one is draining to daylight, how do you incorporate the 100-yr flow rate?

Can you share what daylight looks like for your use case? Where is your target for the water to be managed?

Daylight means a field whose elevation is below the area to be drained in this case

The roof should be shedding to solid drain pipe.

Yes, "should." I've found that should happen and did happen are two very different things when it comes to a lot of homes.

Incidentally, our roof had gutters/drainage originally. We put in our own french drain after about 8000 hours of research, and decided to re-route the roof drainage to right above the new french drain (separate pipes) because the roof drainage broke at some unknown point and was dumping water around our foundation piers (yay...). Well, our roofers came and installed gutter guards after all this, which caused the gutters to shed 60% of the water into the drainage area because of the way they're angled. If we hadn't put in a french drain, it'd be a real problem, but as it is now, it's a mild annoyance that I keep telling myself I'll fix.

You should make them remove the gutter guards. If you're losing by that much water to your foundation, the gutters are kind of pointless now.

I have used French drains on buildings where I didn't want to install and maintain gutters. The roof shed straight into a gravel path (no soil coverage) around the building that had perforated pipe leading to a dry well. Worked perfectly. In one case the pipe had to be very shallow so I used crusher-run (404) aggregate to form better support around the pipe at the surface. Again, worked perfectly. You really have to watch the details and plan things out meticulously for the given situation.

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