This is a HOTBED of a question, depending on who you ask. And it is a killer that causes untold amount of damage into people’s basements. So, we are going to give you the answer now, and explain below:
YES, a Drain Tile ABSOLUTELY needs to be sloped. You wouldn’t install your sewer pipes level, would you? (Any who say yes should relinquish their plumber’s licenses.)
Using Logic
While some contractors will argue that the Drain Tile does not need to be sloped, this usually comes from the following concerns:
- Lack of Knowledge
- They simply do not know any better.
- Laziness
- They don’t want to do the extra work to slope it. Unlike sewer pipes hung from rafters, in order to slope this pipe, you need to dig more dirt. Digging more dirt takes more time and costs more money, thus leaving you with a level Drain Tile that is ineffective and causes flooding in heavy storms.
- Stubbornness
- “I’ve been doing this for 35 years, I don’t need no whippersnapper telling me what to do.” RUN! Run as fast as you can from anyone who ever says this about anything.
The Proper Slope
The basic idea is that water flows better with a slope. Think rivers, they always go downhill. Sewer pipes are all sloped. Drainage in your yard is sloped. Why on Earth would anybody install a Drain Tile without a slope? Look above for those answers.
When you are installing Drain Tile, it is important to slope the Pipe 1/8” per linear foot. This means that every 8 feet there will be a drop of 1” in the pipe. This is vitally important for the heavier rains. Same as your sewer, if it was level, it could handle SOME of the water/sewage coming from your home. But what happens when everyone takes a shower/uses toilets at the same time? You guessed it, a smelly situation.
1/8” per linear foot has been found to be the most effective slope for both installation and operation of the system. If you slope it much more, you will not be able to run the pipes very far, requiring more Sump Pits to pump the water out. Which brings up a good point:
Does My Basement Need More Than One Sump Pump?
We install Sump Basins at 80 Linear Feet of Drainage Run inside a basement for a Drain Tile. This means that if your basement is 160 LF in perimeter, we need to install 2 pits to ensure the Drain Tile stays with the footing. If your Drain Tile runs beneath the footing, you can end up washing dirt out from under the footing, causing structural concerns.
This is why you NEED a reputable, Basement Waterproofing Contractor to do your work, not just any GC who has been “doing construction all my life.” Run from those people.
So, let’s say you have a very large basement. Let’s blow it up. You are now at 240 LF in the perimeter. At 240 Linear Feet, we now need a third Sump Basin and Sump Pump. Once you cross another 80 Linear Feet, another pit will need to be added. This mostly happens in commercial applications with large underground parking garages and storage areas.
How Many Sump Pumps Do I need?
We install Sump Basins at 80 Linear Feet of Drainage Run inside a basement for a Drain Tile. This means that if your basement is 160 LF in perimeter, we need to install 2 pits to ensure the Drain Tile stays with the footing. If your Drain Tile runs beneath the footing, you can end up washing dirt out from under the footing, causing structural concerns.
This is why you NEED a reputable, Basement Waterproofing Contractor to do your work, not just any GC who has been “doing construction all my life.” Run from those people.
So, let’s say you have a very large basement. Let’s blow it up. You are now at 240 LF in the perimeter. At 240 Linear Feet, we now need a third Sump Basin and Sump Pump. Once you cross another 80 Linear Feet, another pit will need to be added. This mostly happens in commercial applications with large underground parking garages and storage areas.
Wrapping It UP
To sum it up nicely:
- YES, you need to slope your Drain Tile
- Slope should be 1/8” per Linear Foot
- For every 80 Linear Feet, you need a Sump Basin. 160 LF needs 2 Sump Basins, 240 LF needs 3 Sump Basins, and so on.
- A REPUTABLE Waterproofing Contractor should be used, not a GC. GCs are the biggest offenders in not sloping Drain Tiles properly.
- Do it nice, or do it twice. We understand Drain Tile is expensive, so homeowners want to save $$. Let me tell you, doing it 2x is ALWAYS more expensive. Do it right the first time with the right company.
Thanks for reading, and as always:
“Not Everything’s better When Wet”
12 Responses
My crawl space is 187’ perimeter and I’ll be doing a French drain myself with 2 sump pits, due to budget restraints. My pits will be on opposite corners of the crawl space. Should I run 1 continuous pipe from basin to basin, with the high point somewhere in the middle? In order to go around the full perimeter, I’d have 1 pipe going from basin to basin for one side of the crawl space, and another pipe going from basin to basin for the other side of the crawl space. I’d make the high point in the middle of these pipes. Any advice is much appreciated. I’ll be using Geotextile fabric and perforated 4” pipe surrounded by gravel and fabric. I’ll also be sloping 1% or slightly more.
Hi Nathan! Great question!
Weather you use one full piece of line or not, it will end up the same as the lines will be cut inside the sump pit.
You should absolutely have a high point at the mid point between the sump pits. From there the pipe should grade down 1/8″ per foot towards each pit. That will make the longest run of the water in the Drain Tile a maximum of 46 ft, which will give you excellent flow capabilities.
You’ve got the right idea, just be sure to put those high points dead center in between the pits to allow for the best slope and drainage.
I would then also recommend you to encapsulate. Drain Tile will take care of standing water, but you will still see moisture and high humidity when it rains in there if you don’t encapsulate. If the crawl space has a concrete floor, ignore that point. :)
This article gives a very accurate and very straightforward answer, Austin. As a local tile installer, I often get this question from my clients and this is a very simple and direct way of putting it into words. Thanks for sharing this.
Thanks, Reed! If I’m anything, it’s simple and direct! HA!
I really appreciate that you write a wonderful article on “does drain tile need to be sloped”. Especially I like The Proper Slope idea that Austin Werner shared with us. This article solves my drain problem and I am gonna share it with my friends and family.
Thanks a lot Austin
Thanks for commenting, Ronald! We’re happy to help and let us know if you have any questions!
Austin
All footing drains should be level the water runs through the stone pipe might not have water in them ever. So much bad info so often!
Hi Russ! A common misconception. Just like sewer lines, oil pipelines, storm sewers in cities, or any pipe that deals with non-pressurized water, you want to slope the pipes. Gravity is our friend, and we need to be sure to slop any water pipe that is not under pressure at 1/8″ per linear foot.
We have run into a lot of General Contractors that think the pipes should be done level. We re-do a lot of those systems because they are unable to handle large amounts of water. Small rain events maybe, but the heavy rain those systems fail.
Another reason GCs won’t do the grading is to save time and money. It takes time to properly grade and install a Drain Tile. So instead, they cut corners and end up installing a sub-par system.
Beware of any contractor trying to install your Drain Tile level the EXACT same as you would beware a plumber for installing your sewer lines level. It just doesn’t work. Find a professional.
Hey man, I’m reading your article and I’m and I’m a bit confused. Your longest run from pit to high point is 80 ft correct? So OVER 160’ perimeter you’d need a second pit. I’ll be doing this job myself in my basement. My plan is basically to put the top of my 4” socked corrugated pipe at the top of the footer at the midpoint away then slope to my pit with the bottom of my pipe just above the bottom of my footer. Gonna used washed rock and dimple board on top of my excavation then up my stem walls. Should I use geo fabric to keep my trench separate from the surrounding dirt? I’m thinking a 12” wide excavation to the bottom of my footer the entire perimeter. Does this sound good to you? Thanks for your time.
Hi Taylor!
Great question. You do not need a fabric in the trench between the dirt and the gravel. You do need to be sure that the 4″ Drain Tile you use has a sock (as you mentioned), and that, along with the gravel, will be more than enough to keep your system clear for most homes. If you are in particularly sandy soil, it may be a good idea to then add that fabric.
I have ground water coming into my sump pump pit continuously. The pump cycles every 2-3 minutes after rain and every 8 minutes when no rain has occurred for a week or two. There are no other water sources besides the drain title. Should I be getting this much ground water going into the basin?
Hi Ronald!
That amount of water is actually quite normal for a typical house. You are definitely in a higher water table area than others, but the frequency of the pump running during and after rain does not alarm me. It always helps, however, to check your gutter extensions and for any pooling of water around your home. Any water from gutters (which on average produce 1,000 gallons of water in a single inch of rain), can lead to quite a bit of water in your drain tile.
The other thing to look out for is the life of the pump. It is likely that the pump will need to be replaced sooner than others, and I would recommend switching it out every 5 years to stay ahead of it.
Overall, as long as the pump is working and you have a battery backup, I wouldn’t worry about the amount of water you are receiving in your system.