Crawl space french drains are optional in many encapsulation projects. Do you need a waterproofing drain in your crawl space? What about a sump pump? These are the questions many homeowners ask when faced with the expense of dealing with standing water in the crawl space.
Remember, a crawl space in need of waterproofing has the potential to create a humidity problem. Humidity problems can lead to mold and wood rot fungus. Wood rot fungus can destroy your homes foundation or at least create sagging floors.
Make sure you don’t make the wrong decision when it comes to a crawl space french drain.
Do You Need a French Drain in Your Crawl Space?
French drains in the crawl space are designed to move standing water to a sump pump. They can also be installed to move the water out through the foundation wall. If you have water intrusion in your crawl space after heavy rains, waterproofing drains are needed. Keep in mind, there are right and wrong ways to install them.
Which is Better, Sump Pump or French Drain
French drains are no better or worse than sump pumps. They each do something unique and many times work together. For large areas french drains are needed to move the water to an exit point, like a sump pump. If you have just a small area of water intrusion, the sump pump may be all you need.
It is possible to install a french drain and not use a sump pump as long as the contractor knows what they are doing. Many of the issues we see with this type of install is the waterproofing drain is not draining to daylight. We have seen them stop in the block wall or just past the footer in dirt.
The NDS Hydraway Drain Pipe
As you can see in the picture above, our french drains use a perforated corrugated pipe, aggregate and sock. The sock keeps soil and debris from entering. The aggregate gives the pipe space to allow water to channel more rapidly to the pipe. The perforated waterproofing drain pipe allows the water to enter and travel to the exit point.
We feel all three of these components are crucial to a proper french drain. No sock can allow clogging and failure. No aggregate can slow water making it into the pipe. During heavy floods this can be a problem. No perforations keeps water out of the pipe.
Installation
I have seen french drains installed above the dirt. I have seen them not connected. I have seen them installed to try to carry water up hill. I have seen them installed with no exit point.
Read our last article:
Crawl Space Encapsulation Sump Pump
Normally french drains installed incorrectly are not noticed for a while (until the next heavy rain). Plus many times they are covered with a new vapor barrier which can also hide its incorrect installation. Hiring a crawl space encapsulation contractor with a great reputation for customer service can protect you from wasting money on waterproofing installs.
Below is a video of a crawl space we had to redo for many reasons. One was the french drain pipe was installed above the ground. There are many other problems with the install of the french drain. See if you can spot them.
I hope you found this information useful. Please comment below if you have any questions or would like to say hello.
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8 thoughts on “Crawl Space Encapsulation French Drain”
Hi, I have ordered the Aprilaire e080 and vent fan and will be ordering anabec advanced cleaning solution plus to fog my crawl space and then do an encapsulation. I’ll also be sealing the other vents and installing insulation on the walls. I would like to install the French drain system myself but not exactly sure of the best way to slope it. For instance, the long back wall of my crawl space is 60ft long and straight. Any ideas of the best way to slope that? My sump pit will be at the low end of that wall trench. Thanks in advance
Hi Nathan, if the crawl space floor is level the inside of the pipe has a built in slope (air space). If you will slope the last part of the pipe that enters the sump pump pit, it will draw the water in the pipe to it faster. If you want the water to move even faster towards the pit, a 2 to 3 inch slope along the majority of the wall with maybe a 4 to 6 inch slope into the pit will move the water quickly into the basin. Keep in mind most footer drains and interior basement drains are not sloped due to the air space inside the pipe that acts as a natural slope as long as the pit/pump is lower than the pipe. Hope that helps.
Hi Michael—
I moved into my house and did a backyard project where I added a retaining wall and graded the land so it was level. In the process— we covered up a white pipe in the backyard that I now know was the French drain from the crawl space. I’ve never been down there— but looked at my inspection report to confirm that there is indeed a French drain (no pump).
Is there anything I need to do since we covered it up with about two feet of dirt out in the yard— or just let it be? The crawl space is partially encapsulated, dry, and I have a dehumidifier down there. This area doesn’t really flood and the French drain never had any water coming out of it.
Appreciate any guidance you can provide
Best,
Amanda
During a heavy rain you could experience water building up inside the crawl space if you removed its exit to the yard. If you notice that, consider a sump pump in the area and tie your interior french drain into it. Hope that helps.
I’ve got water under the house around the perimeter of the foundation after a significant rain. This seems to result in increased humidity levels inside the house (which cause our wood floors to buckle in some areas). Since I don’t seem to have an issue with ground water, would you recommend I first consider French drains around the foundation on the outside of the house, or go directly to French drains with a pump underneath the house? The challenge with doing on the outside of the house is that I can’t access the entire perimeter (garage, front and back porch are on a slab, and one added room is on slab with pavement directly outside-this results in less than 50% of the perimeter to the foundation directly accessible). The challenge with doing this underneath the house is that it is very hard to move around underneath-not enough room to get up on hands and knees, so it’s pretty much belly crawling. And I ain’t a big fella. Thanks.
Hi Sean, this is a difficult situation. Do what you can on the outside with french drain and downspout extensions and in some cases you may need to cut concrete and install surface channel drains as seen here: https://amzn.to/3vDpRUY. I’d also tackle the crawl space as part of the project. We rarely see an outside approach only be effective at keeping water out of the crawl space. I know it will be difficult but not doing it correctly could cause major wood rot and floor damage in the future. Hope that helps.
I’ve encapsulated my 1500 sq ft crawlspace with a 15 mil vapor barrier, installed a dehumidifier, and a 220 cfm foundation vent fan. My crawlspace slopes down to an unsealed gravel filled french drain that drains out to open air with a popup style cap. My radon levels in the bedrooms above the french drain area seem to be quite a bit higher that other rooms in the house. I’ve read that open french drains can bring radon into the crawlspace. How can I mitigate that? Is it as simple as installing a check valve?
You could try a check valve, also is there a vent between the drain and your bedroom that you could install a foundation vent fan to draw air to outside before enters your bedroom?