What is a basement gravity drain

I had an indoor French drain installed in half my basement. Pic shows it done except for the cement on top of stone. There is a 4 inch pipe below the stone and it all goes to the sump pump. I was going to finish the other side myself to save myself about $4000 dollars. I read at some point about something called a gravity drain in the basement where it's all the same work but you don't add the 4 inch corrugated pipe.

What is a gravity drain?

 

I have never heard of a gravity drain. There are many drains made with just crushed stone however. It is often done outside the home along a basement wall so water moving sideways through the soil hits a layer of crushed stone next to the house. The water flows straight down and into the drainage pipe at the base of the foundation to carry it away. I've also used them outside when the grade slopes toward a building and it allows you to intercept the surface water and get it to flow somewhere else via gravity.

If you are going to all the trouble I would NOT omit the perforated pipe in your drain. The pipe is lightweight, inexpensive and it works so after all the other work and expense. Don't go without it.

 

Thanks for the info. Ya, adding the pipe does add more work, more concrete to jack out, carry out and then fill back in but, as I've thought more about it, leaving the pipe out will probably be something I'd regret in the future.

 

Quick question. Can I use any corrugated drain pipe for the drain or do I have to find a certain PSI or something?

 

I would avoid corrugated if you can. The corrugations are great for trapping debris and clogging. I prefer smooth wall pipe as it is easier to install without humps or dips and it's more resistant to clogging. You can use whatever schedule you want but lightweight, perforated PVC is available at most home centers.

 

Orient the pipe so the holes are at the bottom. This allows rising water to find its way into the pipe to be directed to the sump.

 

Funny, I learned that the holes should be on the sides. It allows water to flow into the pipe, and once the water is in the pipe, it'll travel along the bottom without draining back out. So you're not filling one area with water from another area. Once it's in the pipe, it'll be 'guaranteed' to end up in the sump pit or drain area.

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That makes sense, too. When I did my basement a couple years ago the pipe I bought had 2 holes about an inch and a half apart so I guess they were technically on the side a slight bit. Somebody explained it to me that the gravel-filled trench is the real drain and the pipe just helps when needed. Believe me, I;'m no expert but got lots of good info from this site when I decided to do that job myself.

 

The correct method is to have the holes at the bottom. Water doesn't flows downhill. And, water follows the path of least resistance. It will not move sideways into holes in the side of the pipe unless there is something forcing the water to go sideways. You do not need to worry about water "leaking" out of the drainage pipe or being transported somewhere else. That isn't a concern with a drainage system of this type.

The gravel filled trench is primarily there to provide an area where water can pass easily and to act as a filter to keep dirt away from the drainage pipe. If any water encounters the gravel either on the top or sides it quickly flows down to the bottom. That is where the drainage pipe with holes in the bottom comes in. If the water rises at all it flows into the pipe where is has almost no resistance and can easily flow to the drain.

 

I'm about ready to add the drainage rock. Should there be gravel drainage under the pipe as well? Or can the pipe lay on what looks like mostly dirt now that I've dug out the trench?

And a bonus if anyone can help. I'm not sure what the proper mix of concrete mix and sand I should use. When the company did the 1st part of the drain they told me they don't use just the cement mix because by adding more sand it becomes easier to work with when filling the trench.

 

I like to have crushed stone on all sides of the drain pipe. They also sell a fabric sock you can slip over the pipe to help prevent debris from getting through the holes.

Concrete mix comes ready to go. Just add water. Or, follow the instructions on the package. Sand, rocks or more water are sometimes used to cut corners but I've never heard of adding more sand to make it easier to work with. Many bagged concrete mixes, especially those sold at big box stores, use pea gravel for the aggregate which makes it easy to work with.

 

Thanks!

I usually never add anything to the mixes but I didn't know if it was a common thing. I just want to be sure the floor goes back in as strong as it came out.