• Post Reply Bookmark Topic Watch Topic
  • New Topic
permaculture forums growies critters building homesteading energy monies kitchen purity ungarbage community wilderness fiber arts art permaculture artisans regional education experiences global resources the cider press projects digital market permies.com private forums all forums
this forum made possible by our volunteer staff, including ...
master stewards:
  • Nicole Alderman
  • r ranson
  • paul wheaton
  • Mike Jay
  • Anne Miller
  • Jocelyn Campbell
stewards:
  • Devaka Cooray
  • Joseph Lofthouse
  • Burra Maluca
garden masters:
  • Dave Burton
  • Pearl Sutton
gardeners:
  • James Freyr
  • Joylynn Hardesty
  • Daron Williams

french drain pipe - not for water from above?  RSS feed

 
pollinator
Posts: 4437
Location: North Central Michigan
12
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
we have successfully drained 5 acres of our property to a low pond area with french drains around both of our houses and across the land..the property is water table level in some areas and the french drain has worked very successfully here for about 8 years..

guess it depends on the property..ours is mainly clay and Michigan peat
 
Posts: 20
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Juicy. i've read this whole thread. As a landscaper I work with drains all the time and this exchange(above) is just the stuff I am constantly thinking about. The illustrations show a few scenarios. Surface water and ground water... the wish to have soil moisture someplace and the wish to not.
  My land has both underground (ground) water and surface water. I want to build a home-WOFATI sp? seems appropriate. Ground water is both shallow and deep, surface water is plentiful (clay/slow perc). So, swales, packed earth trenches and drains??? what will be the feature hydro solution?
  Considerations: Floor material, need for foundation drains, ground water under the foundation, soil surface and slopes, vegetation, ground/surface water for vegetation, water barriers, add etc.
  If I had an illustrator program...help... I might add here in 2D- but I don't, so, here goes: I will put in a barrier-under a packed earth floor, I would put in a french drain under/beside the packed earth edges, I would use a "paul drain" for surface water interception-sloping towards the house-open at the top, no pipe necessary, I would consider a second, deep(er), groundwater french drain for that interception flowing towards the house (and who knows the perking stratas underneath?) and again, unless there is a hundred feet of drain I don't see the need for a pipe, i've just never seen that kind of flow...and as far as infiltration into the soil, yep-especially at a sandy vein- but to avoid this, hmmm. Paul, I like your  idea of sheet plastic under edges of filter cloth-u-shaped-maybe a foot high, packed earth on the house side and bottom but this is useless if the soil is porous-add clay/bentonite?.
  So surface "paul drain" would be located outside(uphill) of the modified french drain for ground water-which would also be swaled slightly-this could be gooshy, so,  softened uphill with compost and vegetation-if you could afford like 20+ feet. Can you visualize this?
  As far as "foundation plantings?  I would tip the roof to the down hill side as illustrated and have drought tolerant plantings under the (3) foot eve in softened soil sloping away to the packed earth before the ground water drain location-this could be greenhouse area, paved area with surface/gutter drains or better, open to the deep(er) modified ground drain as a surface and ground water drain. Voila!
  The green house idea on the uphill side elliminates a lot of the worry where the scale of this cover is appropriate to the ground/surface water expected. I would certainly invite the water into the greenhouse in a controlled way, so still the need for at least surface drain with options to plug the ends!
 
master steward
Posts: 26715
Location: missoula, montana (zone 4)
bee chicken hugelkultur trees wofati woodworking
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Paint programs are super easy.  What operating system are you using?

I think a paul drain is probably a bad idea for any situation because ... well .... actually I think there are some ways a paul drain could be okay, but you would have to poke some holes in the plastic ....

I think you should start a new thread called "I want to build a wofati."  In that, you need to give us a small idea of where you are and how cold it gets there.  If you have some pics of the building site that would be good.  Annual rainfall would be good.  Do you have lots of trees?  What is your soil like?  How big of a wofati are you thinking of?

I suspect that the use of bentonite would be a bad idea.
 
                            
Posts: 3
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Ok, forgive me if I am getting what you say all wrong, but it seems to me that the problem is with what you expect the french drain to do.  When I see the french drain, I see a method of dispersing standing water aka "puddles" into the surrounding area, not move it from point A to point B which I see you doing with your Paul Drain aka "ditch".  You can think of a similar system employed in septic systems.  Now a thing to think about is that water moves from larger holes to smaller holes and only goes the opposite way under pressure.  That makes me think that the french drain is not meant to move the water table away from your site, but disperse runoff from your roofing.  As you say, there is no point in pointing a french drain uphill as it will have no effect.  I believe however that it is more useful than your ditch as you will not have erosion issues with the french drain.  If you are having issues with a high water table on a perfectly horizontal land, so that water seeps out of the ground, a ditch may be a good way to get that seepage to move down to a lower elevation, if one exists, othewise you will need as someone else mentioned, a pump.

Hope that my 2 cents is of some use.
 
                            
Posts: 3
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
After further consideration, I have changed my opinion somewhat.  I have considered a second possiblity for the french drain.  I was thinking about my friend's field that sits at the bottom of a mountain.  After a good rain, he sometimes gets artisian style springs where the water pressure from the hillside actually causes water to spring a few inches out of the ground.  Even under lesser conditions, a lower flat could get soaked from higher ground.  I suppose in such circumstances a system could be used in reverse of a septic style system to help dry out the land.  In such a case, I could envision creating a french drain running parallel to the hillside.  Such a system may be covered and grass grown on the top.  It would need to empty out into a ditch or something lower than the collection area to work.  It could be used to drain a swampy area and would look better than ditches criss crossing the area.  I wouldn't worry about the holes in the bottom of the pipes.  If you are trying to lower the water table, you don't need to worry about it draining out of the bottom of the pipes as water is already there.  If it could continue going down, you wouldn't have a swampy area to begin with.  I'll bet many swampy areas may be drained this way.  It doesn't need to be fast or efficient, as long as it is constant, it will do the job beautifully.
 
Posts: 369
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
paul have you tried core aeration. Sometimes the soil just needs air in it to slow down  the water. depends on where water problem is but its good for your yard or garden iether way worth a shot .
 
                        
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Awesome Information about french drain. It has been very useful to me.

I even found informative article about french drains here http://www.encyclopediaofhomeimprovements.com/frenchdrains.html

I hope it might be useful to you guys!

 
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
It seems like the french drain has been really misunderstood. I think an important point is that the french drain isn't saving up a puddle of water to soak into the soil, because the gravel portion (we can call this the paul drain portion) also has a pitch.  The paul drain works like a ditch, but has gravel to protect it from plants, as the rate of waterflow increases the water within the paul drain rises and enters the holes in the bottom of the pipe, where its flow is unimpeded, you don;t have to worry about the holes onthe bottom because, in the event that the water table is lower than the pipe there will be no water in the pipe to fall out, during that time you don't need any kind of drain.
 
                        
Posts: 2
Location: No. California, East Bay
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I just found this forum, and have greatly improved my understanding reading through this topic. 

We recently bought a suburban 6600 sq' ft. property which appears to have an improperly done pipeless French drain on it.  I'm wondering if I need to re-do it, and whether it's feasible to create a VERY SMALL water or marshy area to soak up some runoff.  Until I figured out it was a French Drain-ish thing, I was hoping to put garden in that area--does that seem a possibility?

We're in the East Bay of No. California.  In the dry season it's fairly hot and dry, and in the rainy season the water table is at ground level.  Any feedback would be appreciated!  (Low-budget, please ; )

There is a trench filled with probably 1-1/2" river rocks which is open to the surface, about 3' across.  When I dig down about a foot, there is black plastic underneath.  The property is on a slope, with retaining walls above and below (between neighboring properties), and cut and filled so that there are basically 2 flat(tish) levels connected with an intermediate slope.  The rock "drain" is along 2 edges of the property away from the house.  The first edge is along the "downhill" slope and the second edge goes at a right angle on the lower level.  The second edge is possibly contributing to the deterioration of the lower retaining wall. 


Thanks in advance!
 
paul wheaton
master steward
Posts: 26715
Location: missoula, montana (zone 4)
bee chicken hugelkultur trees wofati woodworking
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
There are lots and lots of factors that come into play:

1)  does the land in question have slope?

2)  what is the soil like?  Does it drain well?  Is there lots of clay?

3)  what is the problem that we are attempting to solve?

If you are trying to grow a garden on flat clay soil, then a french drain is excellent.  The soil can be moist and loose and the french drain will keep it from getting too wet.  Of course, there is the issue of where does the water drain to?  If the land is flat, how the hell do you get rid of the extra water?  A french drain does nothing if it doesn't have a downhill spot to carry the water.

I think that for building a structure, having a little water next to the building isn't as good as having no water next to the building.  Especially if we are talking about a wofati - it's better if the soil stays completely dry at all times.  So a french drain can make a horrible situation less horrible, but we need something much better than what a french drain can do.  So the surrounding uphill ditch like things are, I think, a far superior solution.



 
                        
Posts: 2
Location: No. California, East Bay
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks for your response, Paul.

Since my last post, I discovered that 3 sides of the property have apparent informal French drains.  All of the pebble beds are at the edges of the property.  One definitely has plastic underneath.

The pebble bed at the top end of the property, under a retaining wall, is dirt-infiltrated with rosebushes growing as well as buried wood (not obvious why) and has no apparent slope.  Theoretically it might drain back to the lengthwise pebble bed.

The lengthwise pebble bed (with the plastic for sure) starts level, then slopes downhill.

The pebble bed at the bottom of the property (above the lower retaining wall) is not obviously sloped.  It has a lot of plants growing in it.  It may be an attempt to gather water from the other two pebble beds and divert it to ??  Neither top and bottom pebble beds extend all the way to the street.

The soil has a fair amount of clay and doesn't drain that well.

Earlier in this thread, I believe someone said that if there was plastic underneath instead of landscape cloth, it actually made the problem worse, which makes me wonder if all these pebble beds are a big mistake.

So:

A)  French drains would probably be a great idea for this property, to help it drain better--if they drained properly and if they diverted the water either to the street or (preferred) to a water-using planted area or tiny catchment for wildlife water.  I suspect it isn't working properly at this point.

B)  How much of a problem is the plastic underneath?  To make the pebble beds useful, would I need to remove all the pebbles (big job) and replace the plastic with landscape cloth, as well as removing plants and washing out the infiltrated dirt?  Or, since the clayey soil may not drain that well anyway, does the plastic matter that much?

C)  As far as gardening, are these pebble beds wasted space that I "shouldn't" plant in, or is there a way of covering the pebble beds with something and planting a garden on top without ultimately making the pebble bed not work properly?

Thanks!
 
Posts: 211
Location: Missoula Montana
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I used to have what I was told was a "French Drain" in a house I rented in Colorado.  It was basically a PVC pipe that went from the kitchen sink outside.

It was great in the summer, you could water your flower beds.  In winter, it sucked big time.  First of all, it drained into the driveway, creating a huge slippery ice skating pond.  Then it would plug up from freezing and water would be stuck in the sink for days until warmed up enough to thaw and drain.  Sometimes if I was lucky, I could stick a broom handle up the french drain from the outside and it would then drain.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Yeah I think you were misinformed, sounds like what might be called a very primitive gray water system.
 
Rebecca Dane
Posts: 211
Location: Missoula Montana
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Really?  That is interesting--the people I rented from said it was a "french drain".  It didn't work well anyway.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
French drain sounds fancy.

Check wikipedia if you don't believe me.
 
pollinator
Posts: 450
Location: South West France
97
chicken fiber arts food preservation forest garden fungi goat homestead rocket stoves sheep solar
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Coming back to the original question which was whether or not the French drain is for water from above, I'd like to add my experience of using them.

Here in France we have a lot of storms with an amazing amount of rain falling in a short period. I like to recover as much water as possible but when you use the normal roof gutter arrangement, the rain falls so hard that most of it splashes out of the gutters and on the the walls of the building. People often use hanging chains to guide the water away from the walls but over time the gutters sag and get loosened from their supports and become useless.

To protect the walls from the rain the overhangs are far away from the wall and are supported by a stepped arrangement of tiles called "genoise" (Like a cake) and the genoise finishes off the join between the roof and the walls as well as being ornamental.

Parts of the roof without a genoise (Maybe because it's too high to spend hours up there ! ) have a roof slope which flattens out to almost vertical at the edges to force the water away from the walls as in this photo.



Traditional buildings here all have French drains and this shape of roof and as well as being practical they are (IMHO) rather beautiful. 

 
 
            
Posts: 79
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I haven't read every word of every post in this thread, but logic tells me that an ideal drain would lie in a hybred between the 'french' and the 'Paul' drains.  What I am envisioning is a trench that either has a packed clay bottom and sides up about half way, or an impermeable plastic sheet that lines the bottom and part-way up the sides of the trench.  Then, lay in 6 inches or so of round river rock, then the perferated tube (with the holes on the bottom) on top of that, surrounded by more river rock up to or near the surface of the soil.

This would act by allowing ground water that is higher than the level of the lining to pour into the trench, as well as surface water.  This water would be primarily conducted away by the trench itself, until the water level would rise above the 6 inch point, at which time it would enter the bottom of the drain pipe where it would be swiftly carried away.  The ground-control fabric would still be needed on the top and sides of the gravel to a point below the lip of the plastic liner.  This is a challenge to install, but not insurmountable.

The concept is a horizontal view of how a water well works, where the lower part of the casing is perforated to allow water to flow in, while the upper casing is hole free to allow water to flow up and out of it.  Perhaps that is not the best anlogy, but I think you get my meaning.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Why would you want to line the bottom of the trench? Are you afraid of water falling out of the bottom of the trench to where it doesn't matter?
 
            
Posts: 79
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
It would depend on the water table and the soil composition of the area.  Many farmers use drains to carry away excess ground water in marginal areas to dry them out enough to plant.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
but if the water table is already so low that you have to worry about water spilling from the drain into the water table where does the drain get the water to start with?
 
            
Posts: 79
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
As was explained earlier in this thread, most of the water that a french drain is designed to carry off is runoff water from rainfall.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Yes, rain fall brings all the water to the area. The rain dumps the water on the full soil surface. The water then percolates down through the soil and raises the water table. The high water table spills water where you don't want it (like your basement). The frensh drain takes the water coming at it from above, below, and the sides, and lowers the impediment and allows it to slide down the pipe and out of your life forever.
 
pollinator
Posts: 240
Location: Northern New Mexico, Zone 5b
8
  • Likes 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

paul wheaton wrote:

And yet another obnoxious opinion from me:  If you are building a trench for a french drain, and you pack the bottom, you don't pack the sides.  Therefore, water can still seep to the edges - although it will be slower.  And clay soils will make a difference in that there will be a near zero soaking into the soils - although they are more likely to plug.



In most cases, you want water to enter the drain from the side walls of the trench.  That is part of what helps keep the soil from getrting waterlogged.

Also, as you pointed out the perf pipe in the drain only works in saturated conditions (as intended).  The gravel pack around the pipe does a lot to drain soil during/after the intermediate water events.  So it works on two levels.

You would be surprised how much water those small perforations can move.  I have lowered the water table in aquifers many feet with french drains with small perforations (for construction of buildings with multilevel basements).  I am working on an undergroung parking ramp construction right now where we have about 800 linear feet of franch drain on an eight acre site.  We are lowering the water table ten feet for an area that extends well beyond the site boundaries.  You would never know the soil in the bottom of the excavation had been saturated for thousands of years.  It is as dry as the native soil thirty feet higher in the soil collumn. 

The hydraulic conductivity of the perf pipe (even with samll holes) is orders of magnitude higher than the gravel pack which is orders of magnitude higher than the surrounding soil. This leads to a large drying capacity.  In a lot of conditions if you are just trying to keep your foundation dry or prevent ponding the pipe isn't necessary.  But if you are going to the trouble of trenching and backfilling with rock and fabric - why not install the pipe?

Also, in general you don't care what the soil moisture is like beneath the trench/drain.  If you did you would dig it deeper.  Neither a typical french drain nor your lined trench design keeps the soil dry on the bottom of the trench.

 
                        
Posts: 3
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi! Totally new here!

Wanted to drop a note in this thread about field tile. I used to live in an area of central Illinois that was actually, originally, a swamp. Thousands of acres. Which always fascinated me. They used "field tile" to drain it and lower the water table in the area so they could farm. It's simply a deep ditch with less deep pipe laid out in a grid pattern where you want the water table to be. The joints of the tile are left loose but protected from debris so the water collects in the grid and spills over into the ditch where you can do whatever you want with it.

Now, of course, there are laws that protect wetlands so you would have to check on that if you were going to drain a large area. You wouldn't want to upset the ecology of your neighbors land but you could sort of "sculpt" the ecology of your own. Shoot, you change the ecology of an area by creating a pond, so why not a little dry spot? No different than landscaping. Call it "ecoscaping".
 
Posts: 187
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
If water is collecting in a French drain and then seeping out into the surrounding ground to create a problem with the basement then the French drain isn't deep enough. Just dig the damn thing deep enough and you don't have to worry about trying to reinvent it. 

If the ground needs to be bone dry over a wide area, just install a series of French drains.
 
Emerson White
Posts: 1206
Location: Alaska
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
If you were really stupid about it you could make a French drain that moves water from an uphill water table to your basement, but that level of incompetence deserves to be punished.
 
                                      
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Paul, you're really over complicating this whole matter. Your Paul drain will work, but the trough should be inside the filter fabric and under the stone. The only negative is that the rate of flow will be very low, and it would NOT be suitable in conditions where a high flow rate of either ground water or migrating surface water would be the norm. I have put french drains in areas where the ground water constantly ran out of a concrete joint 30' wide on a slightly sloping ramp down to a concrete walk/bike way, 24/7, 365 days a year - unless the ground and the water in it froze. We have layers of clayey soil here that trap ground water above them(picture a pond filled with transmissive soil). In some areas the clay layer is thirty feet down, in others 4 feet. When that soil filled aquifer fills up with water, the water comes out at the easiest place, be it a basement, crawl space, or concrete joint in a ramp with 3 feet of total elevation change. We put the outlet pipe from the french drain into a nearby drainage basin, the pipe constantly flowed water, and the concrete stayed dry and algae and slip free. You could say no surface water was seeping down  into the french drain, and you would be correct. But, the fact is ALL the water flowing out of the drain was surface water trapped in the ground, seeping through the soil and escaping at a pressure release point. This is the same scenario as the builder of the French chateau that is pictured here encountered. Ponds and wetlands are uncovered aquifers that extend underground beyond and downslope from the water you can see. Water seeks its own level even underground. The compacted ditch would work, but the invert elevation of the ditch has to be below the top of the soil that is inhibiting migration of the water to seep to a deeper depth, instead causing it to seep along horizontally. However, there will now be water running out of the side of the ditch and down the slope constantly eroding it. The ditch would serve the same purpose that French drains do, which is to lower the water table in the area they are constructed in. It would just be messier maintenance headache, and an unsightly impediment to the use of the property it is in.  The pipe in the stone in the french drain merely allows for higher rates of flow, which appears to be appropriate for the use in the chateau pictures, since it's keeping a detention pond filled. In the case of the chateau, the compacted ditch would be unsightly, and the paul drain would not provide a high enough flow rate. Remember to, when you visualize this, the bottom of the french drain must have positive slope to a pump, natural outlet, or detention pond downslope from the area being protected. Your picture showing blue perforations in the pipe at the top is incorrect. The more water that can seep in the holes in the bottom, the higher the rate of flow will be. Don't make the mistake of envisioning the holes one at a time. Picture 10, 20, or 100 feet of pipe with water flowing into all  the holes and into the pipe and then down stream, due to the fact that the bottom of the trench is sloped.  Water can shoot into those holes at the upstream end, and at the lower inverts the pipe can be completely full, up to a point near the outfall  and then the level in the pipe will taper down as the flow increases out the end. The only place water can remain in the stone in the bottom of the trench is at the downslope end. If the trench has six inches of fall the water will flow through the stone (as in your paul drain), and eventually get into the pipe further downslope. You're picturing the bottom of the trench under the pipe filled with water at all times. That is not  necessarily the case, unless the flow rate is high. There will be some water at the end of the trench, which should be below the area, or elevation, of concern. If the french drain is extended past the area being protected, which is the proper way to do it, the water can naturally flow downslope out of the stone with no negative effect to the protected area -especially if there is a detention pond. In that case the water would seep through the earth, as it is toward the chateau, and escape into the pond, just as the water was escaping out the joint in the concrete. The benefit is you will never see it and it won't cause erosion.


If you go see a french drain being constructed properly you will get the idea.
 
                                        
Posts: 12
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
has anyone tried the original french drain design? With clay tiles instead of a pipe??
 
Posts: 145
41
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Paul we built drains like this in PA around homes all the time to keep water out of the basements.  As long at the trench  has a pitch away from the property they work fine with no pipe, probably not as perfectly but more then good enough. 

Of course today I would be far more apt to move the water to where I need it vs. try to get rid of it. 
 
                          
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Some idiot has created a "Concrete Floor" along the side of my house and by doing this, has breached the "Damp-Proof Course (DPC)" by 6 to 8 inches. As a result, I get damp and mould forming rising on the inside wall.

Basically, I need to prevent surface water hitting the wall and penetrating, and more importantly, stop the ground moisture coming up the wall (through the capillary action).

I have been told one solution is to dig a French Drain along the wall, by cutting the concrete slab.

Does anyone, especially "paul wheaton", "Kabir424" or "40 years in const." can advise me if this is the soloution? Thanks.
 
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hey Paul,

I'm new to the forums and just reading through, so I'm resurecting an old post, but maybe I can shed some light here. The reason that a french drain works with the configuration as you described in your previous posts, is by the priciple of hydraulic pressure. When soil becomes saturated, it loses it's structural stability and acts in a fluid way, much as a mudslide. The weight of the saturated soil above the bottom of the drain"s "grade" exerts pressure on the water in the soil. The drain, being an area of lower resistance, allows this hydraulic pressure to force the water in the soil into the void of the stone and further, the pipe when the volume is sufficient, regardless of where the holes in the pipe are located. Sort of like osmotic pressure and cells in the body.

Thus the drain allows the soil to maintain some amount of structural strength, keeping it from caving in your basement wall or allowing your concrete footings to subside into the goop. Let's say your footings for your house are 36'' deep and your french drain is 60'' deep. the soil at 60'' deep won't be able to contain a lot of water because of the weight of all the soil above compacting it and forcing the water upwards. Since your footing are 36" above the french drain they rest on 36'' of stable soil, allowed to drain in the french drain. Even if the soil at 60'' deep is saturated, that dry 36'' of soil above that level supports your footing and distributes that force over a very large area and prevents that footing from sinking. This functions much the same way in a basment wall situation, except those forces are exerted laterally, by the soil against the foundation wall. If you are unlucky enough to have a concrete block wall with open cells, they are not designed to withstand lateral load; Only the dead load exerted by the weight of the home. I've had to repair several of these.

This is why you would install a french drain above a structure on a slope. It allows the soil uphill to drain and maintain it's structural strength and to intercept water running down to saturate soil under the structure. Unless the drain runs around the structure allowing the water to emerge somewhere below the structure, it really doesn't function properly. Unfortunately these systems only work up to some reasonable theoetical limit and I doubt any system will handle massive (i.e. 4'' rainfall per hour) for a sustained period. In this situation a swale uphill of the french drain would be of great benefit. I do construction and remodeling for a living.

Picture attached shows what we ideally like to install. Item 1 in the drawing would be some type of EPDM rubber membrane around 1.5' deep, allowing landscape plants to set down roots but channelling large volumes of water to the french drain. Hope this helps!

foundation-drain-detail.jpg
[Thumbnail for foundation-drain-detail.jpg]
 
Posts: 55
Location: Ottawa, Canada
10
  • Likes 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

UKSouth Coast wrote:Some idiot has created a "Concrete Floor" along the side of my house and by doing this, has breached the "Damp-Proof Course (DPC)" by 6 to 8 inches. As a result, I get damp and mould forming rising on the inside wall.

Basically, I need to prevent surface water hitting the wall and penetrating, and more importantly, stop the ground moisture coming up the wall (through the capillary action).

I have been told one solution is to dig a French Drain along the wall, by cutting the concrete slab.

Does anyone, especially "paul wheaton", "Kabir424" or "40 years in const." can advise me if this is the soloution? Thanks.



I had a similar problem in my basement however it was naturally occuring. Who ever built my house just poured the concrete floor in the basement directly on the ground instead of putting a layer of gravel. The ground here has a lot of clay and the water table is high. As a result, if we'd have a few days of rain water would come up through the basement floor.

To fix this we installed a french drain in the floor which led to the sump pump well. This took care of 90% of our problem but there were still occasional small puddles that appeared.

To take care of these secondary puddles I just dug trenches into the floor from where the puddles formed to where the french drain is. Rather than put in a full french drain I just filled the trench with gravel and covered with concrete. This really seems to have done the trick though I still have one final trench that I need to install.
 
Posts: 280
Location: North East Scotland
1
forest garden goat trees
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Having read all the posts I am now totally confused and unsure what will be the best option for us.

I live on a steep slope in an area with very high rainfall and a high water table. I have had a retaining stone wall built to give a couple of flat areas for a garden and I need to do something about the water collecting on the uphill side of the wall. What would be the best way to tackle this?
 
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi All,

I joined the forum becuase there seems to be some knowledgeable people on here who might be able to help me solve a problem. I have just excavated a 5 acre lake near a limestone karst.

We have an abundance of freshwater supplys but unfortunately at the top end of our excavation we have opened up a brackish water spring which appears to be as a result of karst spring conduit which will go all the way to the sea some 5kms away.

the sites 400 meters long and the groundwater is fresh from not far beyond where this brackish spring has been exposed. The spring is clearly source by the mountain which has a cave below ground and sea level....we are only a few meters above sea level and the spring appears to be running underground at about 2.5 to 3 mtrs.

My thinking was if I dug a 5 meter deep trench between the spring and lake bed, all the brackish water would gather in the trench and not reach the lake bed, trouble is I cant leave the trench exposed it has to be filled. what would happen if I place a PVC liner on the lake side edge of the trench and filled the trench with stones? and then a pipe (french drain) just below existing ground water level (the same as ground level give or take an inch)....would all the brackish water be forced up into the pipe where I could steer it away from the fresh lake?

Thanks in advance!
 
Posts: 13
Location: Alturas, CA
1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
So, Don McCarty, I really appreciated your explanation. Just three questions. In your picture, you show a rubber membrane running down the house retaining wall into the ground 1.5 feet and then moving out away from the house "channeling large volumes of water to the french drain".

1. About how far away should the french drain be from the house?

2. How deep should the french drain be?

3. Would it be helpful to have the rubber membrane run down the "house side" of the french drain and cup under it (kind of like Paul suggested on his drain)?

In case answers are situational, my situation is this: I live in the mountains and we only get about 12 inches of rain a year and most of that is in the form of snow. My house is built into a hill (on the South side), and has a full basement (with only a 7' ceiling). The outside of the south facing basement wall is nearly fully covered in soil (so, about 6' of soil is "leaning" against the basement wall ) and this gradually tapers to nothing as you move toward the north-facing basement wall. The basement wall is all concrete block. I have no idea if the block wall is hallow (I suspect it is since the house was built by a "handyman"), or if there was french drain built at its base (again, I suspect it was not given the builder). However, I only have a drainage problem on the Southeast corner of my basement, which has a five foot square muddy spot after the spring thaw, and takes all summer to dry out. I am told I need to install a french drain behind the house (on the south slope), but the soil may be too rocky to get down more than a foot or two. Any advice you (or anyone else) may have would be appreciated.
 
Posts: 111
Location: Vermont
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I installed drainage as a main part of my work for almost 17 years so let me help. The drainage pipe you buy has holes in it to catch the water as it rises and quickly direct it way from whatever it is you are trying to protect. Properly installed it should have anywhere from six inches to a foot of 1 inch washed stone under it around it and above it and the holes should be at 5 and 7 o'clock. On normal days with moderate flows of water the stone does all the work. The pipe is there for real heavy flows which would overwhelm the stone because the stone interrupts the flow a little and can back up when too much water is present. The slope of the pipe and the ditch should be 1/4 inch per foot. You should wrap the pipe in drainage fabric to keep the silt from clogging the pipe.

If you want surface drainage you can use the same system but you have to bring the stone up to ground level and leave it open. I recommend this all the time but it does raise the cost of the project a lot as you need a lot more stone to do this.
The bottom picture works if you ditch is really shallow and you bring the stone up to the surface. I've used this form to catch water off of a roof with no gutters to direct the run off from the roof to a drainage system beneath the ground. http://www.dirtworks.net
 
Posts: 79
Location: Austin Texas
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I added a french drain to pauls pic, see how much less resistance is in the center pipe?
Filename: french-drain.bmp
File size: 478 Kbytes
 
Nathan Wrzesinski
Posts: 79
Location: Austin Texas
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
well that didnt work...
french-drain.JPG
[Thumbnail for french-drain.JPG]
 
For my next feat, I will require a volunteer from the audience! Perhaps this tiny ad?
2019 PDC for Scientists, Engineers, Educators and experienced Permies
https://permies.com/wiki/100059/PDC-Scientists-Engineers-Educators-experienced
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!