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Wet basement cure: interior drain system Carson Dunlop Associates Use an Interior Perimeter Drain
to Stop or Prevent Basement Leaks & Water Entry

Basement perimeter drains, French Drains, or B-Dri/Beaver Basement type basement de-watering systems:

This article series discusses types of interior perimeter drain or what some call a "french drain" for stopping foundation leaks or preventing wet basements and crawl spaces.

We describe the basic types of exterior and interior foundation drainage and de-watering systems for homes.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Basement Perimeter Drain Systems for Basement De-Watering: Installing & Inspecting "French Drains"

Basement de-watering system (C) Daniel Friedman

Our page top drawing of types of indoor foundation and basement drainage systems is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

A perimeter drain, as we explain in this article,

 is an indoor drain cut into the floor around the perimeter of a basement or crawl space to intercept and remove water from the building interior.

We illustrate perimeter drains and we comment on their effectiveness and installation details below.

[Click to enlarge any image]

Interior foundation perimeter drains typically intercept water leaking through a foundation wall or around the building wall/floor slab intersection.

The intercepted water is conducted to a sump pit and sump pump for disposal, or it may be conducted to a location from which it can drain by gravity.

Some people call an interior perimeter drain used for basement or crawl space de-watering a "French Drain".

Whatever you want to call it, an interior perimeter drainage system cut into the basement or crawl space floor can effectively stop basement or crawl space flooding - or can it?

In our opinion an interior drainage system can work to keep water off of the floors, and properly installed it can also resist sending problematic high moisture levels into the building as well.

Wet basement cure: interior drain system Carson Dunlop Associates

But before installing a costly basement interior drainage system, it makes sense to check and repair obvious outdoor water entry sources that send water through the building foundation walls. That is especially true if the outdoor water entry causes are trivial and inexpensive to cure.

See EXTERIOR WATER SOURCE ELIMINATION

and BASEMENT de-WATER vs GUTTERS.

Carson Dunlop Associates' sketch (above) shows three different approaches to installing an interior drainage system to stop basement flooding.

What are the Definitions of a French Drain, Footing Drain, & Perimeter Drain?

French drain sketch (C) Daniel Friedman

 

Well plenty of people do call interior foundation drains or perimeter drains a "french drain". We don't.

A "French Drain"

 is an outdoor buried drain line constructed to carry water away from the building, typically to a drywell or catch basin. Our sketch shows how we remove water from roof runoff that pours down a downspout.

Details about French Drains are

at FRENCH DRAINS

So what is the difference between a french drain, a footing drain, and a perimeter drain. A French drain is shown above, and a footing drain is shown in our two sketches below.

A footing drain, 

that is an exterior foundation drainage system placed outside the foundation wall near the wall footing, at the level we show, covered with gravel, and if the footing drain going to do anything, it is piped to daylight or to a catch basin that is in turn pumped to daylight or to a storm drain.

Wet basement or leaky basement prevention and cure  (C) Daniel Friedman

Details about footing drains - exterior foundation drainage systems - are

at FOOTING & FOUNDATION DRAINS

Footing drain sketch(C) D Friedman

Are Indoor Perimeter Drains a Foolproof Cure for Wet Basements ?

Basement perimeter drain detail, excerpted Journal of Light Construction Dec 2005

Skip the exterior excavation and waterproofing - an interior perimeter drainage system can work just as well, according to Scott Anderson, The Journal of Light Construction, December 2005 [1].

Watch out: our OPINION is that while Mr. Anderson offers good design details for a basement interior perimeter trench and drain system, and though he reports success with this system, we think it's mostly appropriate for an un-finished basement in a home where high moisture from water running down walls is not a concern.

Even then, depending on design details and how high on the wall a plastic water barrier is installed, you may be pumping un-wanted moisture into building air, inviting a mold problem.

If a basement de-watering design is successful only at keeping water off of the floors, that is if it does not also keep excessive humidity from passing into the basement through walls and floors, the building is still at great risk of high indoor moisture levels, condensation problems, indoor mold, and related troubles.

The basement WaterGuard™ interior basement drain system described in this article shows water running down the basement wall and into the drain system.

Also we notice that the perimeter drain in the example installation is routed to an indoor sump pump that sends water up, out through the basement wall, into a short plastic drain pipe extending about 18" away from the foundation, and thence into an open plastic trench on the ground surface.

If that basement water disposal system is blocked by snow and ice, the sump system will simply stop working and the basement will flood, possibly worse than ever as we have also drilled openings to improve flow of water from the foundation wall into the interior perimeter drain.

Wonderful. And nothing is stopping evaporation of water from the wall surface into the basement area where it causes indoor humidity to skyrocket.

We discuss the importance of protecting the sump pump discharge from freezing

at SUMP PUMP DISCHARGE

and at WATER ENTRY/DAMAGE PREVENTION WITHOUT GUTTERS we discuss designs to keep water out of the building when we can't keep gutters on the roof edges.

Photos of Basement De-Watering Systems: B-Dri™ and Beaver Basement™ types

Below we show two implementations of the type of basement perimeter drain de-watering system sketched above.

Below you can see that a trench was cut into the floor and something was buried there, along the foundation wall: typically perforated pipe in a gravel-filled trench that slopes around the floor to end at either a sump pump pit or if you are lucky, a spot where you can drain water out of the building to daylight using just gravity.

The installer left a 1/4-inch gap to encourage water that runs down the wall to flow into the drainage trench.

This system will usually keep water off of the basement floor quite successfully but it does little to keep moisture out of the area as water evaporates from the wall surface as well as flowing into the trench.

Basement de-watering system (C) Daniel Friedman

A second common basement de-watering system shown next (below) is also an indoor foundation perimeter drain system like the one we described above.

But this installation includes heavy plastic that extends a few inches up the wall, perhaps to encourage water to run behind the plastic and into the gravel trench.

Basement de-watering system (C) Daniel Friedman

This approach also covers up an ugly wet water stained row of concrete blocks at the bottom of the foundation wall. Early B-Dry™ type basement drainage systems used this approach.

At contemporary B-Dry™ and similar installations that we have inspected the installers have shifted to running this heavy plastic barrier up the entire face of the foundation wall, right up to the sill plate.

We like that improvement as it should dramatically reduce moisture movement into the room itself as water runs down the wall and into the drainage trench.

In that system one is, of course, unable to see the foundation wall to gain any understanding of just when and where water is entering the structure.

Trenchless Basement Water Interception Systems

Basement de-watering system (C) Daniel Friedman

A "Beaver Basementâ„¢" de-watering system is a simpler basement perimeter catch-and-drain system.

In the installation shown here for a Duluth Minnesota home, the basement dry-out approach uses what looks like a heating baseboard to intercept water passing down or through the foundation wall.

Water runs inside a channel, around the room, and into a drain or sump system. This system, omits the step of cutting open the basement floor to install gravel and drainage piping to the sump.

Depending on the source and quantity of water leaking into the structure, this less costly installation might work.


Basement de-watering system (C) Daniel Friedman ... Basement de-watering system (C) Daniel Friedman

This article series includes article excerpts or ideas reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-01-28 by InspectApedia Publisher - gap between my basement floor and the cinder block wall

@GT,

That looks like a floor inlet for an interior perimeter drain basement the watering system. If you close it off you may find you have water on the basement floor.

Since a lot of water under a floor slab tends to significantly reduce the level of radar gas and filtration up through the floor it sounds as if some further investigation is needed to see which problem you're going to to prioritize.

On 2023-01-28 by GT

I'm trying to figure out the purpose of this gap between my basement floor and the cinder block wall. I'm interested in sealing it up for radon mitigation

On 2020-05-12 - by (mod) -

It nay help me offer a useful comment if i can see a photo. What are we sealing, against what sort of leaks, exactly where - indoors, outside, roof, surface or other water control?

Mere guessing risks wasting your effort or worse, fouling up a drainage system and causing building water damage.

Help me out with more information and I'll be glad to work out some suggestions with you.

On 2020-05-12 by Louise

QUESTION :
I have the B-Dry system in my basement.

I NEVER had a wet basement or wet walls and was sold a "bill of goods" in order to help "reduce the humidity in the basement. After paying a lot of money to get this system installed, I later learned that there is an underground stream that runs under the driveway side of the house. The basement, as a result of this drainage system, vents the humid air from the french drain into the basement.

I WOULD LIKE TO PLUG THIS VENT UP WITH A SILICON 40 YEAR CAULK

IS THERE ANYTHING THAT YOU CAN TELL ME ABOUT THE OUTCOME(S) OF SEALING the corragated plastic piece that runs just above the floor down to THE FRENCH DRAIN ON THE DRIVEWAY SIDE OF MY HOUSE?

Years ago, I ripped the plastic off most of the walls and patched the walls. But the vent going into the drain is corrugated and moisture can get into the basement.

I use 2 powerful dehumidifier for a 600 foot basement every summer. So far, that has been the ONLY effective way to reduce the humidity.

On 2019-11-14 - by (mod) -

Sorry Adam but I don't have a specific recommendation. Talked to the contractor and satisfy yourself that there's someone who will answer your questions and put your mind at ease. Talk to your neighbors to see if you can find someone who's had a good experience with a local contractor.

On 2019-11-13 by Adam

Hi..I'm based in Montgomery Country in Maryland. Thanks for this article it was really helpful and confirmed my suspicion that there is no magic bullet in solving water issues (and that I know nothing about this topic). We have this clay bowl effect at my house. Only once in the past 25 years have we had a leak in the basement, and this happen over the summer (2019).

A small pinhole leak came through the bottom of the foundation of our unfinished basement. I'm wondering if you had any recommendations for a Maryland company who is honest and straight about what the best solution would be. If you have any recommendations I would appreciate it. Thanks, Adam

On 2019-10-15 - by (mod) -

Re-posting without advertising link

WCP said:
Thanks for the article! Would love to share some of your stuff with our visitors at Waterproofing Cincinnati Pros

Moderator reply:

You are welcome to refer readers to this or other articles at InspectApedia.com

Please don't copy our content;

We very much welcome critique, questions, or content suggestions for our web articles. Website content contributors, even if it's just a small correction, are cited, quoted, and linked-to from the appropriate additional web pages and articles - which benefits us both. Working together and exchanging information makes us better informed than any individual can be working alone.

On 2019-10-04 - by (mod) -

D.

I am not sure what sort of membrane was installed, nor where, nor how, on your home, but in general, a water-proofing membrane is not sound-proofing.

If there is water entering through the foundation wall or up around footings and if it's entering the perimeter drain system then yes, you might hear water flowing. Hopefully that indicates that the perimeter drain system is - so far - working to keep water from entering the rest of the building.

On 2019-10-04 by D .House

is it normal to be able to hear water flowing inside interior perimeter drains, after a membrane has been installed ?


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