How a French Drain Works
This article talks about how and why a french drain works.
You can also watch a video that illustrates how water flows through the gravel and into the perforated pipe.
A French Drain is a perforated pipe surrounded by gravel. It is used to collect water from a low spot in the yard. The pipe is usually 4″ Perforated (holes or slotted) and is encased in 3/4 inch washed stone.
Catch basins can be added to this system to help collect immeadiate water run off. The pipe needs to discharge downhill from the low spot in the yard. OK.. That’s the basics. Now let’s look at a typical problem we find in a back yard or side yard…
Usually when we get a call to give an estimate we find a couple of things almost always.
- A landscape company has come in and tried to mobe the water away from the low spot.
- The grade of the yard slopes towards the house . When it rains, water floods the area.
Its great that your landscaper wanted to try to help, but since it didn’t work and you have called us out, we know the problem is worse than before they tried to fix it. Our congrats to the landscaper, but if you are going to take on this project, Do It Right the First Time!
To make a French Drain work (yard drain) the trench should be deep enough to allow water to flood from the bootom of the trench up through the gravel into the pipe. The way the system works is:
- a gravel base is laid under the pipe .
- the holes in the perforated pipe point DOWN
- Gravel is added to surround the pipe and cover the pipe.
- gravel should be be brought to grade (the level of the sod) .. If this is not possible, then a fabric (soil seperater) needs to be added to cover the gravel so dirt can be put back on top and sod re-laid or re seeded. If this is the case, catch basins must be added in a series to allow immeadiate water run off. (the gravel brought to grade works BEST with additional catch basins in low spots)
- As water drops into the trench, it falls to the bootom of the trench. It flows through the voids inthe gravel VERY QUICKLY.
- Holes are pointing DOWN becuase it allows the fastest pick up (collection) of water into the system. If holes are pointing up to the top of the pipe, the water tends to saturate the soil casuing the wet spots to remain long after the rain.
Discharging the water
This is very important and its kind of a No Brainer. Water needs to run downhill. The discharge must be lower that the deepest part of the trench. To make this happen, there must be a down hill run away from the area. Someties we have to trench through a hill to get good slope for our system to work. (this is usually the case since the water is getting trapped in th elow spot to begin with.
If there is no downhill run away from the area, in other words, if the pipe is running up to discharge, it will not work. So what can be done?
We suggest and recommend installing a sump pump. The yard drain is the same as described above but it discharges into a sump pit where the sump pump lifts the water up and can push it up hill to discharge. The pump we most commomly use is a ZOELLER M 53 (mighty mate). This pump can easy lift the water to ahead (total lifting capacity) of 25′. Its extremely powerful for a small 1/3 of horse power submersiable pump. The pit is 24 inches deep which allows for great water collection and allows the pump to easily cycle the water. We install a solid lid on the pit making secure and safe. The pump discharges water through a 1 1/2 inch PVC pipe. (while this sounds small, it works great and is more than enough for most applications) .
Lastly, there needs to be an electrical outlet installed next to the sump pit. This is because extension cords are not to code for a sump pump. They work, but its better to have a GFI Electircal outlet installed.
Ok! So when you are ready to have a True French Drain Installed, Give us a call. We’ll be happy to take a look and write you up a FREE Estimate. Our estimates have drawing with proposed drainage and ALL associated cost.
We Do Complete Rainwater Drainage!
Tags: AL, apple drains, AR, average cost, back yard, BASEMENT WATERPROOFING, CA, CATCH BASIN, CHANNEL DRAIN, CHARLOTTE, crawl space, CRAWL SPACE WATERPROOFING, drain, drain tile, FL, footer tile, frech drain, GA, grade, GRAVEL DRAIN, home inspection, IN, KY, LA, MI, MN, MS, NC, NY, OH, OR, PA, ROOF DRAIN, SC, SD, slope, TN, TX, unspection, WA, waterproofing, WI, wood rot, WY, YARD DRAIN