Ultimate Guide to French Drains

this is sean with gate city foundation drainage in this video i want to talk about some french drains i want to talk about how i do them and the rationale behind some of the methods that i use and i think there's been a lot of confusion and questioning about why i do things the way i do and one thing i do feel like is that these things really work and so that's what i'm going to be doing in this video is talking about each of the components why i do it the way i do it and then i'm going to go back and revisit most of the french drains i've done and see how they're flowing a common misconception is that a french drain is a place to send water to and so you you i hear customers say i need a french drain for my gutters but a french drain is a collection device it's a it's a system to collect water so what kind of water is a french drain collecting is collecting non-point water and so first of all point water sources would be like a gutter downspout or a stream coming through the yard something like that where you can point to it and say that's where the water is coming from non-point water is when you just kind of have water everywhere in the backyard maybe flowing down a slope or maybe coming out of the ground somewhere and so that would be non-point water so what we need to do with the french drain is is situate it and use it to collect non-point water in this clip you can see an area of yard that's just completely saturated with water when you look around the yard you see that we are pretty much sitting downhill from this big slope right here and so what you have going on is a lot of water just just flowing down the hill and then standing right here here we are on the side same thing a lot of water just standing around here so this is all non-point water a good good candidate for our french drain here's another example of a hill that water is fall is flowing down and look at all this standing water just sitting right here this is several days after our rain further in the backyard you can see more standing water and this water is just leaking out of this retaining wall right here and it's just standing right here in this one area all the time so this is non-point water and this is what a french drain will correct when looking for the location to place your french drain you need to keep a couple things in mind the first thing you need to keep in mind is that water flows downhill so you want to make sure your french drain is in the low point and you want to make sure it's in the path of your non-point surface water and so placing the french drain is absolutely critical to its functioning so we'll talk more about how you how you can achieve fall from where you are because that's another big consideration if you're down in a basin a bowl there's nowhere to drain it out of and so you've got to be at a low point where your water is going to collect but you've also got to be at a high point where you can take that water once it's into a pipe and take it downhill from wherever you're at so it gets a little bit tricky this is a good example right here in this low point take a look at this hill that you have you have a huge hill sloping right down into this foundation and so you want to situate your french drain right in that low area because placement of the french drain is so critically important i spend a lot of time talking with customers and asking them to to give me video or pictures of where the water is coming from where it's going that sort of thing so take a look at this picture here you can see that from about right here-ish to down over here by the fence we have water that's flowing across here and so the water is coming from the opposite side over here at the fence and it's flowing across here and so this picture right here tells me that if i put a swath of french drain across there that that will represent a barrier that water cannot cross and when i looked at this also this was a low point over in here and so this picture right here tells me that this is where your french train wants to be if you're talking about excavating and trucking in a bunch of gravel and doing a bunch of digging and trenching then it makes perfect sense that after you do all that labor and all that work to throw in a quality pipe before you cover it back up so we only use schedule 40 solid thick wall pvc pipe for our french drains and for all our other gutter work and drainage work as well so don't be tempted to use a corrugated pipe for a french drain they are not the right pipe to use because they just clog up and hold water and they're just inferior to pvc okay i wanted to show you really quickly the pipe that we use so we use only solid schedule 40 for our drainage install so here is a nice little pile of pipe and we purchase this perforated schedule 40. the problem is this stuff is no longer available for my supplier and so what we've been doing is we've been making our own perforated pipe so we string a chalk line and we use the letters as our first line so i'm keeping this stick right here we've been using that as a template and so we've been drilling our own perforated pipe so here's a piece right here that's just a little uh piece of a nipple that's left over from from a job so let's take a quick look over here i've got this pipe set up pretty much so i've been playing around with this for a while i've got this set up pretty much like it is in the trench so we have about uh eighth of a bubble or so of fall right there eighth of a bubble of fall right there sixteenth maybe there's maybe a sixteenth of a bubble there there's a sixteenth of a bubble there there's another sixteenth of a bubble and there's a 16th of a bubble okay so this is my perforated pipe the holes face down and you hopefully can see in there see what's going on in there and so basically i like this pipe because it leaves a an area for debris to roll along so i just harvested a bb or a marble out of a rattle can so i wonder if this thing will make its way through that pipe so here we go and that's in about an eighth to a sixteenth of a bubble i don't know if you can hear that or not but it's rolling through there all right let's see if we got anything coming out over here [Applause] i can hear it look at that okay so that is why we use schedule 40 perforated pipe for our french drains because it is a high quality pipe and any debris that gets in there is going to get blown out so there's the marble test out of six nothing not even at a quarter bubble so that's why we use this stuff so again my thought is if you're going to go through all the trouble to dig a trench haul dirt away haul gravel in why not throw a quality pipe in your trench before you cover it up i want to show you another very important aspect when you're looking to place your french drain so this water here what this represents is it represents water that is sitting on top of impermeable soil so these native soils here do not let water flow through them if if water flowed through these soils this water wouldn't be here right now and so we know that we need to get rid of the soil get it out of here and we need to put gravel in this place because water falls through the spaces in gravel whereas here this soil this native soil is impermeable to water and so the water is pooling on top of that that soil so we need to get rid of that soil so i wanted you to take a look at what's going on here here we have wet slop right here but once you get down a few inches you can see that we've got dry dirt and so what that means for a french drain is it means that this is all surface water that's just kind of hanging around here it's probably flowing down from the hill and it's probably staying at this level so when we dig this out and put gravel in here what's going to happen is all this is gonna ooze into the gravel fill up the trench like it's doing right here and then it will flood into the holes of the perforated pipe and then it finds a path of least resistance down to the curb and so that's how a french drain works it's a it's used to collect non-point surface water here's another really good example you have standing surface water on the left right there and as soon as you start digging you hit super dry dirt and this is telling you that the native soils here are impermeable to water so you've got to get rid of that soil the water will not flow through it so if you put your french drain in here and then put that soil back on top of it you'll be in this exact same situation the water will not flow through the soil into the drain this is a french drain that i was pretty much working by myself on for the second day so we had to leave this the first day and this is what i found when i came back the next day so just let me pause it real quick there and take a look at how much water is in there and so those impermeable soils we were just talking about those are what is that soil is what's going to make your trench become a basin and so the water is going to flow into the trench it flows through the gravel and it it collects there if it floods up in the trench like it's doing here and then it flows it finds its way into the perforated pipe with the holes facing down and then it flows through the pipe so you can see right there that i i left that untrenched and so that's why it's holding water like that so that's a pretty cool example of how a french drain collects water into the trench once i get that cut out right there then i will be able to take that water through my pipe down to the curb this is a project we've been working on and we're doing a french drain here and so it's just been raining a lot so we got stopped after our first day we got our trench dug but this really shows how the french drain is going to work before the french drain goes in and so if this thing is going to work your water's got to be able to flow downhill by itself and so take a look at what's going on here you can see the trench just got a lot smaller because we're going to be doing solid pipe across this section but it doesn't matter if the pipe or the water is flowing through a pipe or through a trench it's all flowing downhill and so that's a cool example of how a french drain works without the french drain in place so this this project if we can ever get it finished will be coming up at some point before we talk about gravel we've got to talk about the volume of dirt that comes out so take a look at the volume of dirt here that's coming out of this trench now we didn't put that much volume of gravel back into the trench so how can you have more volume coming out than going back well the dirt will fluff up a little bit so i'll give you that but i'm digging this for the with a machine so it's not fluffing up terribly too much and the rest of the volume is air is open space in between the pieces of gravel and so that's why it's critical to use angular gravel because angular gravel locks into place it doesn't shift around i see a lot of people on youtube using rounded washed river rock for their french drains now you would never want to use this because it shifts around and it lets the soil move through it and so river rounded river rock will clog up with soil whereas angular rock locks into place angular rock is the only choice for drainage work and that's because when it gets compacted it locks into place and it doesn't flow around so if you have ever looked into how to build a retaining wall for example it says you've absolutely got to use angular rock for that same reason it locks into place it doesn't shift around it provides a stable base and so when you're doing your french drain you've got to have that angular rock in there so that the the spaces between the gravel pieces are preserved if you have rock that's shifting around a lot what happens is the dirt gets into it and can can get through it when the angular rock locks into place it forms a filter so the rock is the filter that's why you use angular rock let's take a look at the idea that the gravel has a lot of open space in between it so what i'm doing here is i'm just filling in that area where we had all that water sitting and what one of the things you're going to notice is i'm putting in a ton of volume here and the level of the water is not going up by very much and so if you remember your soil science class or earth science class you know that the smaller the particle is the soil particle the more it holds water with clay being pretty much the highest water holding capacity so here you have giant pieces of gravel and so these aren't going to hold any water so the water is going to flow right through there and so as soon as i finish filling up this trench i'm going to open it up and let it go and we're going to see just how well water actually does flow through this gravel and so there's there'll be no question about it once you see me let this thing go the idea here was to let this water go after i dug the trench so i wasn't working in mud but this is what a french drain so this is what this once i get this pipe in here this is what the pipe's going to do the french drain is going to collect the water like a french drain should my solid pipe is going to carry it to the curb i wanted to show you how strongly that's still flowing there and that is a testament to the fact that the gravel basically lets water flow through it and so the water gets into the gravel it freely flows gets into the pipe and then carried away i get my gravel from the local quarry here and in this part of north carolina we've got igneous rock here so this is all granite that is uh quarried right here locally for me so my truck is by by far the smallest truck in this quarry but they're happy to load me up and i'm over here all the time it seems like doing drainage work getting gravel this clip shows a crawl space that had been flooding and so we put a french drain across the front of it right there and that french drain represents a barrier that water cannot cross and so you see there that we leave a space of dirt in between the foundation and the gravel same kind of thing water flows through the gravel so you would never want it up against the foundation this ship this clip shows very well how water can't cross gravel so you see all the water sitting there on the left hand side and on the right hand side we've got 20 or 30 inches of gravel and the water can't cross that barrier the reason water can't cross gravel is because water falls through gravel and so this is something that can be useful if you're trying to collect water into a trench as in a french drain but it can be very very bad if you put gravel all the way up against your foundation so you would never ever ever want to put gravel all the way up against your foundation because the water flows and falls through the gravel and so take a look at this clip where a previous french drain was installed a few weeks before i came by and it just made things 10 times worse and the homeowner was just at a complete loss she didn't know what to do she was being told different things from different people and she had spent a bunch of money and her her basement her daughter's bedroom was flooding worse than ever before and perhaps most importantly is the landscape guy put gravel right up against the house and so you know the water flows through gravel so by putting it right up against the house that's just literally letting the water go right through there and so this french drain is just it was inferior products and it was installed incorrectly after you lay your first layer of gravel in the trench you want to get that sloping down and that perforated pipe sloping down to about an eighth of a bubble or so maybe even a sixteenth of a bubble going downhill and so what you don't see in my videos is just how much time we spent this is a 25 minute clip right here that i've sped up and so we spent a lot of time working on this to get it right it's got to be right for it to flow right your perforated pipe needs to be just about level so we slope it downhill maybe a sixteenth of a bubble or so maybe an eighth of a bubble the reason we do that is because when the water floods into the trench the water is going to be level so if you have your pipe sloping down way too much then the water that's in the uphill side of it's not even going to be able to get into the pipe so that french drain needs to be sloping very very gradually almost level for it to be completely utilized for for absorbing water from that french drain from that trench as the water floods up again because the water is going to be flooding up at a level the water is level here we are at the end of a french drain and we're just transitioning into solid pipe and so we're just realizing that this outfall here this this solid pipe is nowhere near dropping the way it's supposed to in fact it's sloping in the wrong direction and you can this is you don't see this in the videos you see how that thing is sloping the wrong way you see how we're standing there and we're both kind of upset that we're going to have to re-dig this thing we've already dug it once and now we got to go back and re-dig it and so that outfall has got to be a full bubble for the french drain to work the water's got to have a path to get out of the french drain very very quickly here's some third person of me talking to the camera there and showing you that each one of these fittings is dropping at a full bubble once we're leaving the solid pipe here and so every one of my workers has a level and when you put a level on a pipe and it says it's falling you know you're good to go unless the level says you're falling you gotta re-dig it this next clip is from our most recent french train and so you've seen most of this clip already but watch what happens after i get my level on the pipe that leaves the y so i find out that it's it's leveling out and what you didn't see in that in that picture is that i we had to rip that pipe back out of there and cut it down a little bit more until we got a full bubble i just didn't get a chance to film it and then we're transitioning into solid once we get out of the french drain we're we're going to aggressively fall so you can see now we're at a full bubble there right there on that coupling or that y and we're trying to maintain a full bubble the whole way down this hang on guys this thing is flattening out a little bit it may be tempting to just throw a pipe in a trench and cover it up and get paid and leave but it's not going to work so i found that with drainage work you really can't fake it if your crawl space is flooding before the before the drainage system goes in it better be not flooding after the drainage system goes in there's just no way around it so you have to get that pipe right and and even though we oftentimes have to rip the pipe back out of the out of the trench and retrench it by hand i still think it's easier to do that right then at the time than it is to have the system not work have a customer that's not happy have to come dig the whole thing back up again so it's just easier and better for everybody to get it right the first time so that's what we try to do the most ideal way to put in a french drain is to have it be open on both sides so think of like a horseshoe around the back side of a property but in the case where you can't do that and you have to have it stop basically at the end we put in a clean out and a youtuber early on named bob the slacker suggested that we drill some vent holes in there and i completely agree with that so that's what we do now as we drill vent holes in our plugs on the cleanouts so there's our clean out and that's also since we drilled some holes in it it's also acting like a vent for the top of the french drain and we've got our two cleanouts right here of course we drill holes in those to vent it whether or not you use fabric around your gravel in a french drain is probably the second most polarizing topic on youtube right behind pvc versus corrugated so this is just my opinion on it my opinion on fabric is the fabric is like a millimeter thick and it seems to me that a one millimeter of fabric would clog up way more than several inches of gravel would clog up and so my philosophy is preserving the flow of water and we already talked about how the faster the water flows the higher the larger the particle it can carry so if you have water that's flowing really hard it's going to carry more debris away if you slow that water way down try to make it go through a fill a piece of filter fabric the filter fabric is going to clog up the flow is going to go down so that's why i don't use filter fabric i think it restricts the flow too much this next bit of advice goes back to the fact that a lot of people think of french drain as a place to send water to so i've seen over and over and over again where they dump their gutter water into a perforated pipe that is then buried along the foundation so you would never ever want to do that you once you have water in a pipe keep it in a pipe until it's gone and out of the way and some place where it's gonna not cause any more problems so you would never ever ever send water that's already in a gutter pipe into a perforated pipe even though it may be tempting if you've got a perforated pipe a french drain and you're trying to catch a gutter right by it you wouldn't want to send the gutter water into the perforated pipe that would that would be counterproductive to what a french drain does which is trying to get water out of there we just turned this corner so i wanted to take a look at what's going on here so this is our perforated pipe and this one is our solid pipe and so it may be tempting to drop that gutter water into the perforated pipe but my philosophy is if you've got water that's in a pipe which is the hard part keep it in the pipe and so you already saw over here there's our clean out for the french drain and we we drill some 3 16 inch holes for venting in there and then this one is just for the gutter and it passes right by it so you saw us messing around playing with this pipe the solid pipe there has to be falling the french drain and the solid pipe has to be falling about a quarter bubble the the french three in the perforated pipe wants to be falling maybe about a sixteenth of a bubble and the reason is because when the water floods into this trench water is going to be level so if your french drain if your perforated pipe is falling too much it's not going to be level like that so coming across this corner here we worked really hard we want to make sure that once we once we pass and turn the corner that everything is falling really hard and what that does is that gives a really easy escape route for that water so starting with this coupling this this long sweep 90 right there we're following a full bubble everywhere so you can see that falling a full bubble everywhere and you can see on down to the creek take a look at this drainage system that this homeowner recently had installed she paid a lot of money for this drainage system and her crawl space is still flooding extremely bad whenever it rains and so i wanted to show you here the what they did here is they took this into a perforated pipe and this was all buried we just uncovered it so what this does what this type of pipe does is it takes the tremendous amount of water coming off the roof and it puts it underground and it's got nowhere to go because it's not daylighting out to anywhere and it's just seeping out of the pipe so you never ever ever want to use perforated pipe after you've caught water in a pipe in a downspout you never want to put it into a perforated pipe a perforated pipe is used to collect water not used to disperse water especially underground especially near the foundation i have a lot of people commenting on the appearance of my french drains after we're finished because we do take gravel all the way to the surface we don't bury the french drain in dirt and wrap it up in fabric again we emphasize the most possible flow so it is a consideration are you more interested in results and getting the water out of there or are you more interested in how it looks afterwards and so my my customers are usually experiencing severe drainage issues usually their crawl space is flooding it's a real estate deal it's trying to close they are their their land is washing away they're experiencing severe problems and so every one of my customers has been fine with leaving the gravel all the way to the surface so they plant they may plant some plants around it they may put some uh natural stone over top of it some more decorative stone they may put some paver paving stones make it into a walkway make the french drain into an edge because it is a straight line so i just wanted to comment on that really quickly that the the appearance is an issue but in the cases where i'm actually moving it a tremendous amount of water customers have decided that results are more important than appearance and this most recent french train i did the homeowner texted me back and said she had given me the go ahead to do it called 8-1-1 got her on the schedule she texted me back she said the husband didn't want gravel all the way to the surface and i pretty much texted her back and said i don't really know of another way to do it besides gravel all the way to surface and i left it at that and i i kind of implied that i didn't want the job if we couldn't take if she wanted me to bury the drain in dirt and that's been the case with other customers too if if i don't feel like i'm going to get good results i'll pass on the job so again we emphasize results over looks i want to end this video by taking a look at some of my french drains that i've previously installed and going back and taking a look at seeing how they're doing so i know i've talked about a lot of things in this video and these are really my opinions and so of course opinions vary but one of the things i wanted to do with this video is i wanted to back up my practices with results so i want to go back and see okay do these practices really work are these french drains really working are they still flowing after the install so let's take a look here i am at another french drain i did now look at this one this one's flowing as well so that much water is just now finding its way out of here this was the french drain that we did these are some friends of mine so harvey my concrete guy poured the slab they had this built and that was our french drain across the front of their shed right there hey sarah hi how's it going good how's this french drain working great we hadn't seen water up under there haven't seen any water since we did it and it's trickling out over there huh the water's trickling out oh is it okay yeah we haven't had any problem with it that's what we want to hear tell us what used to happen here uh the water used to come up in here flood up right here just go up under right here and just run up under that you can see it all the time okay so we put our french drain in right here yeah right yeah and now that water's yes drop out of here okay it's dry you can see us drive under the building there yeah yeah it is take all the pictures you need that's helped us a lot this is that job where we did a french drain and a patio with a big channel drain in the back of it so take a look look at all that water coming out of there that is a lot of water and there's the channel drain right there so there's a bunch of or that's the french drain right there there's a bunch of water coming out of that too and take a look at this yard compared with this yard so that's that right there is the competitors french drain and here's our french drain now it does have gravel all the way to the surface so we're going to do something here that's a little bit more decorative but the point is when you put gravel on top all the way to surface it flows flows like mad and that's what it's supposed to do this is a job where we did a french drain on this side of the house it was part of a real estate deal and look at a look at what we've got going on here so that is a bunch of water coming out of there and this side of the house this is all french drain so this is all non-point water there's no gutters hooked into this side of the pipe so that's all water that used to be landing back there and flooding their crawl space so that's pretty cool this side is hooked up more to gutters so we got a few more gutters right here and look at all that water coming out of there so it's probably been i don't know over a year since we did that one and no curbs here so the outfalls look kind of bad but they were much more worried about getting the water out of here and getting the deal closed than in what it looked like so we were good with that and the sellers were too and the buyers were too i just wanted to mention really quickly on that last clip the inspector came back out after we finished our drainage work it probably been about a week or so since we finished the work and we threw in some air movers to help blow out the crawl space and drive things out but it it it had been pouring by the time the inspector came back out there and he came back out there during the pouring rain and there was no water in the crawl space and he was so impressed that he got my card and the seller's agent got my card as well as the buyer's agent so like i said before you can't fake these results either the crawl space is flooding or it's not this is a job where we did a really big french train he was his basement was flooding so let's take a look at that outfall so look at all that water coming out of there so that's all water that was landing in his basement and it's been i don't know a couple summers since we did that job so that's always a fun one to revisit too because it's always crushing this is another french drain we did a while ago and it looks like they put up a fence and some other cool stuff since i bought the place but anyway take a look at that this outfall so look at all that water coming out of there and if you remember that's all water that was landing under their deck back there and so this was another another one that was part of a real estate deal so that one's been working really well i know i was just out here yesterday but it's been raining all night and it's been raining for about two days so i wanted to take a look at this outfall and see what it was looking like so again this is all this is just that short french drain there was about 30 feet with two legs of perforated pipe so no gutters going into here look at all that water and that's all water that was running under their stairs under their deck across their yard and then across their driveway so that is a lot of water and that's a good testament that that french drain works really well for collecting non-point water this is an outfall that i like coming through so this is a one of our early drainage systems from a couple summers ago so let's see how our pipe is doing look at all that water and this homeowner has reported back that she hasn't had a lake in her backyard ever since we put the system in so i always like coming out to that outfall because it's always gushing i'm going to end the video right there so i hope you've enjoyed watching this video i'd like to thank you for watching it and everything i've talked about in this video i really wanted to to back up with demonstrable evidence so flow are these things really flowing and so keep in mind that i'm here in the southeast and so these practices are working from our soils here our soils are mostly clay and so if you have soils that are sandy you may be doing things differently so keep that in mind as well another thing i want to mention is if you like this video and would like to see me talk about maybe like channel drains or catch basins i've been thinking about doing a video on those two topics as well similar to this where i talk about the the ideas and theory behind it so let me know in the comments if you have any comments about this video or questions about it and i'll try to address those thanks again

Channel: Gate City Foundation Drainage

Views: 134,586

Rating: 4.9392953 out of 5

Keywords: How to install french drain, fabric in french drain, french drain, yard drainage, gravel french drain, when to use french drain, greensboro french drain

Id: bEVBOEIktr4

Length: 40min 59sec (2459 seconds)

Published: Wed Feb 17 2021