French Drain Engineering Questions


#1

Well I am trying to plan a french drain project to alleviate water coming into my basement. I’ve got a lot of engineering questions, if anyone can guide me in the right direction I would appreciate it! First some background. As you can see from the picture, my roof has a main section that then runs down in the front to a patio roof angle in the opposite direction. The problem is my attic is finished with vaulted ceilings, so that this melts the snow, runs down to the patio roof, and forms ice dams in the gutters. This is an issue I’ll address at another time hopefully, if there is even anything I can do about it.

The symptom is that I am getting water in my basement in the coal room that is below the patio. To help solve this, I plan to install french drains all around my house. The front of the house is labeled, and there is a steep grade that goes towards the rear of the house. On each side of the house are cement steps, which are attached to my neighbors houses. My plan is to dig a trench between the steps and my house, lay down fabric liner, put down 2-3 inches of washed gravel, lay the french drain on top of this, fill the trench with washed gravel, then lay 3" of red lava rock covering the whole surface area between the cement steps and my house. I think (hope) this will work pretty well and look nice as well, but I have a few questions:

  1. How far in " do I want the drain from the house on each side?
  2. How deep do I want the pipe to be sitting in the ground? Remember my goal is to prevent water from seeping into the walls in my foundation.
  3. What is the best way to route my drainage pipes from the downspout to the rear of the house down the grade? Right now there is flex tubing running just underground down the house to the rear from the downspout, can I connect this to the french drain (I’m thinking no?) if not how should I route it so it doesnt interfere.
  4. Do I want the holes up or down, assuming they are on one side?
  5. Do I want to use solid piping or flex piping?

Right now grass is in the front and dirt on the sides, so I am hoping this solves my water problem, and also gives me an opportunity to landscape around the perimeter of my house. Which brings me to my last question, will it be safe to plant anything in the front of the house, like a shrub, or will roots interfere eventually with the drain?

Thanks for any insight you can provide!

http://www.thechangingtides.com/french.jpg


#2

Cheap way out: Run your downspouts directly into yard drains at each termination to a swale or somewhere away from any other structure (you choose) and pour concrete 2-3 ’ out and slope it away from the house. This will probably do it for your immediate problems but if you want to adress the whole issue…

The waterproofing way should be done like this… dig out the whole foundation to expose the top surface of you footing. Clean the vertical surface by pressure washing and let dry. While the wall is exposed you should waterproof the whole wall up to 6" above grade and at least 4" onto the footing from the stem wall with Barrier Guard ($) , Miradri system ($$$), or xypex ($). Install drain board over waterproofing if the system requires it. Put a 4" perforated drain running toward the low grade of your home as you have diagramed ( ridgid pipe is better than flex but either will work) with a sock on it at the foot of your basement wall on a bed of 3/4 " or 1 1/4" gravel. Backfill the footing with a minimum of 12" of gravel on top of the drain before adding excavated materials.

If you dont go all the way down you will only be capturing some of the surface water that is seeping through the topsoil around your house but you wont be doing anything to keep water that makes it past your drain out of your basement.

You might try putting Barrier Guard system or xypex on the inside of your basement walls first and see if it works. About 50% of the time it does. negative side waterproofing is a little tricky.

Good luck


#3

I don’t have the time to answer you right now since I’m at work, but I will get back to you. In the meantime, realize that a French drain will only function for a few years before it becomes clogged with silt.


#4

put a clean out pipe somewhere and you can flush the silt out. wouldnt the filter sock keep most of the silt out? especially if it is set in gravel???


#5

maybe! I was under the assumption that the french drains terminated above grade at the rear of the building pad. Perhaps our inquirer will elaborate. Maybe cerb has a critique for us.


#6

Alright, I’m back, but it is now late at night and I’m getting ready for bed. In the meantime, I have a couple of questions. You are willing to dig a French drain, so I can assume you are not opposed to digging around the house’s foundation? Also, how deep is your basement, i.e., half a story or more? Does the problem seem to come strictly from roof drainage, or ground saturation?

Here are some quick answers and products/manufacturer’s to look into. First of all, if it is a hydrostatic problem, it is best addressed with drainage board installed along foundation/basement walls. Mirafi makes some drainage board, and then there is some referred to as popcorn board, but I can’t remember who makes it. Naturally, it would be great if you could waterproof your walls with a product like Bituthene, but that is getting costly and requires some rather extensive work. With regard to a French drain, you want to get the water away from your house as quickly and easily as possible, and to lower ground or a storm sewer system. You will need lots of gravel, perforated drain tile, and a good filter fabric. I’ll be back no later than this weekend to get more in depth if you need, but I would like you to fill in some of the blanks in the meantime.


#7

Thanks for all the responses! The problem seems to be somewhat from ground saturation, exacerbated by roof drainage when I had ice dams. It dries up once my gutters melted, but there is still a dampness present. I am willing to dig, though digging up my whole foundation would sure be a heck of a chore. At its deepest point I would guess the foundation is 7 feet deep, getting possibly a foot less deep every 4-5 feet, as the grade goes downhill.


#8

I pretty much asumed that was your case. Where is the property?

Like I said if you want to get out quickly… it might not solve all your problems but running drains at each down spout and taking that water out of the equation will do alot. Pouring concrete sidewalks and sloping away from the house into other yard drainage will at least keep the water away from your house foundation.

But if you want to solve your waterproofing problems. You need to dig out you foundation and waterproof your stem walls and install drainage.