How to plan, prepare for, and engineer hand excavated french drains should be on foremost on your mind if you are a homeowner planning to install french drains of any kind or description. Do yourself a favor and learn why hand excavated french drain installation work excels at groundwater removal, and how you can do it yourself. Perhaps.
The proper way to install hand excavated french drains requires many steps of planning and orderly preparation.
Remember to start with a plan to create at least 2″ per 10 lineal feet of downhill grade on the bottom of your hand excavated french drain, not 1″ in 10 lineal feet as some websites recommend. That is not enough grade, even if everything else is done correctly.
1. First off, look at your home site from a completely different set of eyes than you normally use. You will be looking at the topography of your home site, and how the grade slopes, if any, and which direction, away from or sloping to the foundation wall.
The topography of the ground surrounding the foundation of the home has everything to do with how the groundwater is removed from the area, and how quickly that occurs. The speedy flow of groundwater running downhill away from the foundation wall can by itself many times prevent saturation and leaking below grade into the crawlspace or basement.
Ask yourself, if the compacted soil grade at the foundation consists of a compacted grade of at least 6 inches per 10 lineal feet away from the foundation, you would be in compliance in most cities around the U.S. with respect to getting a grade permit for building a new home foundation?
That is the minimum grade suggested. Greater is good too. A splash block covered with a thin layer of the same river rock that was installed in the hand excavated french drain, will prevent erosion.
A flat sloping compacted splash block away from the foundation is a first objective prior to the excavation of your hand excavated french drain. Use the dirt and clay coming out of your dry well excavation to do all your compacting and grade work prior to engineering the installation of your hand excavated french drain.
2. Determine first if you have an acceptable place for a drywell or daylighted vent that is at least 10-15 feet away from your foundation area. In this article I will deal with a drywell as your vent. The recommended minimum setback for a 4 foot deep by 4 foot in diameter hand excavated dry well is 10 feet from the foundation. Further is better if you can make the lineal distance work while engineering the slope properly.
I will caution a do it yourself homeowner who is planning on taking this kind of advanced home drainage work on without extensive reading of the material in my website, and using the information to test their ability to plan and physically accomplish the work by doing a small project first, then taking on the main problem area.
Just see first if you can finish a dry well excavation 4 feet deep by 4 feet in diameter, compact the soil around the foundation walls properly, and the stage will be set for you to proceed with hand excavated french drain installation aqua duct itself, connecting the dry well to the collection area approximately 18″ from your exterior foundation wall.
No one ever said this was easy, hang in there.
3. Where is the excavated dirt from the drywell, approximately 2 cubic yards, and the hand excavated french drain excavation dirt, approximately 1 cubic yard per 20 lineal feet in average depths of 8″-18″, going to go? This first of the excavated dirt will be used to compact a better foundation grade, and the rest raked out in the border areas of the yard somewhere if possible, creating new planting areas when amended with better top soil.
A drop box is an expensive alternative to finding a spot on your home site for another raised bed. Add better soil to the mix prior to planting in it however. Usually the border areas of the lot are the best for this excavated dirt placement.
4. The most damaged area from groundwater is usually the crawlspace or basement. So, for best results, target these areas by installing the hand excavated french drains on the outside of the foundation, approximately 18″-24″ from the foundation wall if possible.
Remember, the objective is to dry out the border of dirt from the inside of your hand excavated french drain to the foundation wall, and all the way down to the foundation footing. This will stop the groundwater saturation and hydrostatic pressure that causes the leaking below grade. The professional knows when they are looking at a dead end situation however, where a homeowners experience with the subject is often not enough to make the determination of where, if, and how to proceed.
5. When a compacted splash block against the foundation is completed with the first of the dirt coming out of the dry well excavation, which is done first prior to starting the hand excavated french drain installation, you are ready to take on the installation part of the hand excavated french drain aqua duct that will be the structure of your hand excavated french drain.
If you can raise the grade at the foundation around 8″-12″ and compact/grade the soil back to where the grade becomes flat again, which should be about 18″ from the foundation wall, you will have a great run off to the inside of your hand excavated french drain.
Sometimes foundation vents are too low in the foundation, or siding is installed too low against the foundation, and this will prevent raising the grade at the foundation wall. If this is the case, you have lost an important logistical value added feature of your drainage system, but it is still best to install the hand excavated french drains, as this is your only hope for removal of, and reducing the weigh of, the groundwater at the foundation walls, which causing the penetration, saturation and leaking below grade of groundwater caused by heavy rains, not underground rivers, springs and water slides, as some sump pump installers will try to convince you.
This compacted foundation grade splash block of dirt and clay will run rainwater away from the foundation that would have otherwise soaked next to the foundation as a result of rain running down the outside of the homes siding, and off the roof gutter system when it rains hard. This is extremely important, as well as the engineered flat hard slope of your hand excavated french drain installation.
6. Start the hand excavated french drain at the drywell, at the deepest place in the hand excavated french drain itself, and proceed with your excavation up the grade of the hand excavated french drain. This is really important. If you are caught in a down pour while under construction, groundwater releases and flows out quickly on the bottom of the grade you have completed.
You don’t want numerous people digging randomly in various areas of the excavation at the same time, creating areas that will become sloppy puddles in the rain. This will create puddles instead of a hand excavated french drain aqua duct that is constantly running groundwater within the hand excavated french drain system to the completed hand excavated dry well. Straight sides and a flat bottom, with absolutely no dirt or debris in the excavation. That is your objective. No dirt. None at all.
Step the shovel down on both sides of the 12″ wide hand excavated french drain and wiggle it back and forth. Then pull it out. Break out the dirt with shallow cuts so the sides of your hand excavated french drain remain intact and upright and don’t break off.<
p> Finish the hand excavated french drain with a flat shovel bottom after the point shovel bulk work is completed. This type of work will stand tall in many inches of hard rain without caving in, even prior to the addition of a perforated pipe and 3/4″-1 1/2″ river rock to hold out the sides for long lasting functional purposes.
7. You want to engineer your hand excavated french drain system to cover no more than 50 lineal feet for proper effectiveness, staying with the proposed grade of 2″ per 10 lineal feet. The objective is to be approximately 18″ deep at the drywell and 8″ deep at the top end of the hand excavated french drain.
This example is for the installation of hand excavated french drains on flat surfaces where you must make your grade. Measure according to grade markers and determine a smooth upward bottom for your hand excavated french drain that loses 2″ per 10 lineal feet. See it, measure it, and make it happen exactly that way.
If the topography of your site along the foundation is sloped, and you have a stepped foundation, and your grade is in excess of 2″ per 10 lineal feet, you can excavate up the grade without varying your hand excavated french drain depth. Everything else stays the same. If that is the case go about 18 inches deep all the way through to the drywell.
If only a gradual slope of not enough to make 2″ per 10 lineal feet, engineer your grade as advised in the first option, starting at the drywell 18″ deep and proceeding up the hand excavated french drain to a depth of 8″ deep.
8. If the length of your affected area is in excess of 50 lineal feet you are best advised to split the grade. Create two drywells on opposite ends of the hand excavated french drain system and start with the excavation of both dry wells.
Using the example of 100 lineal feet, make the following your objective. Excavate to 18″ deep at both drywells and slope up to the middle of the system at 8″ deep and 12″ wide. This is called splitting the grade. You still have a grade of 2″ per 10 lineal feet by doing this.
Always excavate from the lowest part of the grade at the drywell looking up towards the shallower end of the grade, because an optical illusion exists if you look at it from the side or above it going down grade.
It is alright to take the bulk out of the hand excavated french drain system facing down grade, but finish the bottom with a flat shovel while you are looking up grade for professional results and protection in not going flat in your excavation. Finish about 3-5 feet of hand excavated french drain completely to grade, and then continue up the grade. You will see what I mean if you ever do it.
9. First fill the drywell to within 18 inches of the top grade, which is the base of your hand excavated french drain installation at it’s deepest. Next roll out the 3″ ads perforated pipe on the bottom of the hand excavated french drain to the front of the drywell.
I find it best to pick up the roll of perforated pipe with a shovel held side ways through the roll, and spin it off straight from the bottom of the roll without making any twists in it.
Stake the top shallow end of the pipe with crossed rebar to hold it down to the bottom of the hand excavated french drain aquaduct.
Put your shovel on the rest of the pipe while adding the rock, this pins it to the bottom of the hand excavated french drain. Start at the deepest end of the hand excavated french drain at the drywell, when filling the system. Stop filling the hand excavated dry well and the hand excavated french drain with 3/4″-1 1/2″ river rock 4 inches from the top, and place a layer of weed cloth covering the width of the hand excavated french drain, shiny side up, and top the entire system off with 3/4″-1 1/2″ river rock. Leave room to reconstruct sod if required. Best to leave all rock exposed if you can.
It’s a done deal. You did the deed. Success is yours. Congradulations you have earned it. It wasn’t as easy as you thought was it?
Install hand excavated french drains. Don’t mess up your chance to get one shot at it. You only have bearing hard soil to excavate once. After that first attempt, the soil is loose and the creation of a hard compacted bottom for your hand excavated french drain is not possible if you have gone too deep. You can compact it and tweek it some, but it is never quite as long lasting and effective as the system that was excavated the correct way, the first time through.
Don’t go looking for information on hand excavated drywells or hand excavated french drains on web sites that specialize in nothing. Seems to be alot of bad information on general construction method sites, or landscaping sites. Use a professional home drainage contractor for all hand excavated french drain installations and for proper placement, engineering and the best results for your home drainage project.