# French Drain Help Please



## moze (Dec 10, 2010)

Hello Everyone
New user here, just found this forum and its great :thumbup: .

I am kindly asking for some advice regarding french drains. I have a drainage problem around the outside of my house, so i decided to put in a french drain. I found a company that i liked, but they said that when they install a french drain, they do not use a gravel bed BELOW the drain pipe. However, they do put gravel on top and to the sides of the pipe. Also, they are putting a sock around the pipe, and felt on top of the gravel to prevent dirt from going into the pipe. My question is, is the gravel bed on the bottom of the pipe necessary? his reasoning seemed reasonable, which is that he wants all the water to get into the pipe, and not escape into the gravel bed below and get trapped. at the end of pipe, there is a box a good distance away form my house that will overflow and move the water away. 

Him not putting gravel on the bottom is not a matter of cost, because i called him today and offered to pay for extra gravel to be put on the bottom, and he said that if i wanted it, he would do it for free since gravel isn't that expensive. BUT he said that he never had any problems with his method, so im confused. he also said he spends a lot of time sloping the drain, so there should be no problem there. 

So,what do you all think about not putting gravel on the bottom, is it bad?

I really appreciate any advice i can get

Thanks


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## Bondo (Dec 8, 2007)

Ayuh,... You don't need gravel Under the pipe,...
The explanation by your choosen contractor is Dead On, Right....

Water leaches into gravel...
Water lays on top of hardpan, 'n will flow out the pipe...


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## hoz49 (Nov 6, 2010)

http://www.easydigging.com/Drainage/installation_french_drain.html


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## Daniel Holzman (Mar 10, 2009)

The gravel underneath the pipe is not necessary, however the explanation about water leaking into the gravel is bogus. The purpose of a perimeter drain is to collect groundwater which is ALREADY in the soil, and direct it into the pipe for transport to daylight or to a sump pump. If you have gravel underneath the pipe, that gravel will be saturated, just as the soil adjacent to the gravel will be saturated. Water will NOT flow into the gravel, since there is no driving pressure to push it into the gravel.

If the drain functions correctly, the water level in the pipe will be approximately level with the bottom of the pipe. Due to gravity, the water will flow downhill to the sump pit, where it is pumped out, or to a low area where it will drain by gravity. It is not even necessary that the pipe be pitched, it can be dead level, so long as the sump side water level is maintained lower than the bottom of the pipe. I design my commercial drains level, it is easier to verify correct installation, and they work just fine.


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## Bondo (Dec 8, 2007)

Daniel Holzman said:


> The gravel underneath the pipe is not necessary, *however the explanation about water leaking into the gravel is bogus.* The purpose of a perimeter drain is to collect groundwater which is ALREADY in the soil, and direct it into the pipe for transport to daylight or to a sump pump. If you have gravel underneath the pipe, that gravel will be saturated, just as the soil adjacent to the gravel will be saturated. *Water will NOT flow into the gravel, since there is no driving pressure to push it into the gravel.*





> which is that he wants all the water to get into the pipe, and not escape into the gravel bed below and get trapped. at the end of pipe, there is a box a good distance away form my house that will overflow and move the water away.





> Water leaches into gravel...
> Water lays on top of hardpan, 'n will flow out the pipe...


Ayuh,.... Just *What* are callin' Bogus,..?? 

The choices of words may not be the best, but the theory, 'n explanation are Still reasonable, 'n *Accurate*...

Having been diggin' ditches for the last 35 or so years,...
My experinces Fixin' Engineer's dreams has taught me alot about engineering, 'n Engineers...
I stand behind what I said in my 1st post in this thread....


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## fornews (Dec 12, 2010)

Hello everyone

I too am about to install a french drain along with drains for some down spouts.

It seems the consensus is no gravel under pipe but gravel on top and sides of the pipe with the pipe slots to the bottom. Rely on the sock to keep the dirt out of the slots. Sound correct ?

I've read a lot of the information at this link
http://www.easydigging.com/Drainage/pipe_tile.html (see picture at bottom of that page)
and I'm a bit surprised to see what appears to be a down spout draining into the french drain pipe and then draining out from there. Does it make sense to have the down spout drain flow through the slotted pipe and then out or should the down spout connect past the slotted pipe or have a totally separate drainage pipe ? 

Thank you,
Jon


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## Bondo (Dec 8, 2007)

> Does it make sense to have the down spout drain flow through the slotted pipe and then out


Ayuh,... Sure, Why not,..??


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## GardenConcepts (Jan 21, 2010)

You'll still get the water flowing from the downspout through the slotted pipe, but some water will escape. Why not use a solid pipe for the first 10-20' and then switch to the slotted pipe? Speaking of slotted pipe- I prefer the perforated pvc pipe for french drains. The black slotted pipe is 'corrugated' and tends to trap silt and debris inside the pipe.


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## AllanJ (Nov 24, 2007)

Downspouts from the roof edge gutters snould not be routed into the French drain.

I don't like the idea of a sock around the pipe but instead lay the sock or filter cloth down first, then add gravel, then lay the pipe, then add more gravel, then fold the edges of the cloth up and over the top layer of gravel over the pipe.

With the cloth warpped directly around the pipe, the cloth can cling to the pipe and only the small circles of the cloth directly over the holes in the pipe will admit water and be sensitive to clogging by dirt.

Water outside and below the pipe will remain there whether that water saturates the dirt directly under the pipe or sits in a layer of gravel directly under the pipe.


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## concretemasonry (Oct 10, 2006)

The bottom of the perforated drainage material should be a couple of inches below the bottom of the footing. This will allow the water under the footing to be removed and maintain stability and possibly reduce any settlement.

It only makes sense to put a permeable soil under the drain tile to increase the area of drainage and reduce the velocity and flow of fine grain soil that can plug an unmaintained drain tile.

"Gravel" is really a meaningless local generic term that means different things in different zones. Coarse crushed rock is bad to use because it can clog easily because of the water velocity draining into it is higher. With rock one or two layers of filter fabric (one around the drain tile) and one to separate the rock from the native soil. The fabric is protection if the right fill is not used or is not available.

When you consider all the work and cost, fabric is a cheap investment.

The older drain tile systems that were commonly put in to drain water from lower area originally never used fabric because it was not available decades ago when they were built. Some contained to drain tile. They just used the proper soil blend in the trench and they are still fuctiong decades later.

AS Allan said, downspouts should never be connected to a drain tile system, since it is a good way to flood a basement or get the drain tile plugged with roof debris. The downspouts should be discharged into a solid wall pvc pipe.

Dick


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## AllanJ (Nov 24, 2007)

When installing a new French drain in or around an existing building, you may have to forego the luxury of catching water below the foundation. You cannot excavate alongside the footing below the level of the footing bottom without danger of having the footings and foundation shift.


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## concretemasonry (Oct 10, 2006)

Allan -

Absolutely wrong!

You are not excavating under the footing, but alongside the footing at a lower elevation to collect water and lower the level of saturated soil. For most soils, you just avoid the area under the footing and side an area from the outer toe of the footing and extending downward and out at a 45 degree angle (conservative). Since most footings are much wider than necessary (typical prescriptive code built-in insurance), the excavation may be closer.

What it boils down to is that that if the bottom of the excavation is 6" below the footing, in general the drain tile center may be 6" away from the footing, which will provide room a pervious backfill to be about 4" wide when measured from the pipe., which is reasonable. You can split hais by an inch or so based on geometry and have to move the pipe out an inch or so to make things look good on paper.

In most instances, the good permeable backfill will provide more structural restraint than most backfill for the oversize footing an wall that is much thicker than necessary. This action will be a structural improvement over most basements. The vertical load on a basement wall and footing is usually minimal and footing width is usually determined by the overly thick wall, so a wall 2" thicker usually has a wider footing than is necessary for the soil conditions.

The removal of the moisture around and below the footing actually increases the structural strength.

Dick


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## bsmith95610 (Feb 14, 2011)

*Drain Pipe Question*

I have a question on the french drain why use perforated piping? Everything I've read says that you should use perforated 4 to 6 inch piping with the holes facing down. But wouldn't water go out the holes instead of traveling through the pipe?


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## concretemasonry (Oct 10, 2006)

The holes are on the lower portion (4:00 and 8:00) of the pipe profile to collect water from a deeper level. Any water entering gets drained away. Usually, the bottom or invert elevation is set slightly below the elevation of the bottom of the footings and a few inches away to not disturb the area of influence of the footings. The pipe should be level since water seeks its own level.

The drain tile is a collector of water and directs it to a sump or daylight depending on the water table. It is not like building a reversed swimming pool since you have to drain away the water.

Dick


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## AllanJ (Nov 24, 2007)

bsmith95610 said:


> Everything I've read says that you should use perforated 4 to 6 inch piping with the holes facing down. But wouldn't water go out the holes instead of traveling through the pipe?


There is nothing wrong with having water go out the holes 24/7. Trouble is, the ground outside the holes may already be saturated so no water would go out the holes. Then the purpose of the holes is to let water in the pipes and over to the sump pump pit rather than let the water level rise and let water come out onto the basement floor.

If the pit is not pumped out properly then the water leve in the pipes will rise anyway and water will come out onto the basement floor. 

The pump should turn on before the end of any drain pipe as seen in the pit is more than half submerged. Sooner if there were dales (bellies) and hills in the piping further back and in some areas the entire bore of the pipe got submerged before the end as seen in the pit gets submerged.


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## bsmith95610 (Feb 14, 2011)

concretemasonry - when you say the holes are on the lower portion if I have a 30 foot retaining wall that I am going to be putting a french drain in. Would I have a 30 foot long pipe with only holes in the last four to eight feet? Is that what you mean by "The holes are on the lower portion (4:00 and 8:00)"?


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## JoeLena (Nov 30, 2010)

No, he means use a rigid PVC pipe made for this purpose. It has holes the entire length, on the bottom sides. This makes the water drain better and has no ridges like the flexible black stuff. The added bonus is you can snake it out if needed.


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## AllanJ (Nov 24, 2007)

When installing the pipe you turn it so holes are more or less facing down. The holes don't have to be exactly on the bottom (6 o'clock positon).

If the holes are higher up then the pipe will not collect water until the water level rises higher, to overflow from the surrounding saturated soild into the otherwise empty pipe.


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## Steeler99 (Jan 30, 2011)

right allan, water isn't going to flow directly down and magically all go to the holes if they were on the top. If they were on the top, water would have to fill around and above the drain to seep in.

The main thing is to have the bottom of the pipe be below the bottom of the footing to ensure that the water table doesn't rise to the bottom of the footing


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## jomama45 (Nov 13, 2008)

Is this french drain actually going at the base of the footing, or just below grade a few feet?


Just for the record, we often put an inch or two of stone under any draintile that lays on already saturated soils. It merely keeps any "soupy" mud out of the pope during const. and backfill. Any stone/gravel material that will allow water to perculate through it will also allow water to perc. out of it. Meaning I've witnessed many applications where the water will drain out of the stone rather than the pipe itself, merely because of gravity.


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