Footing drain sketch(C) D FriedmanFoundation Drains - Footing Drains to Prevent Foundation Leaks & Water Entry

  • FOOTING & FOUNDATION DRAINS - CONTENTS: Footing drains defined, installation specifications, troubleshooting advice. Foundation Drains: definitions, installation details. Definitions of french drain, footing drain, perimeter drain. Foundation waterproofing methods
  • POST a QUESTION or READ FAQs about foundation drains, footing drains, and perimeter drains used to keep water out of buildings

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Foundation drainage:

This article discusses building foundation drainage: footing drains, used to prevent foundation leaks and building water entry. This article series discusses types of drainage system s, including foundation drains or "french drains" for preventing wet basements and crawl spaces.

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Foundation Drain Systems - Footing Drains

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

[Click to enlarge any image]

Our page top drawing of types of indoor foundation and basement drainage systems is provided courtesy of Carson Dunlop Associates.

Article Series Contents

Definitions of a Footing Drain, French Drain, & Perimeter Drain?

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.

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 for DOWNSPOUTS

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 perimeter drain 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 above.

Footing drain sketch(C) D Friedman

The drain shown in the sketch above is intended to describe an exterior foundation drainage system. This drain is placed outside the foundation wall in the location shown, is sloped to drain, and ideally drains downhill away from the building carrying water "to daylight".

Interior Trench & Drain

An interior trench and drain system is sometimes added inside a basement or crawl space that has a flooding problem. If you imagine the drain pipe shown above located on the interior of a foundation wall then it's an internal perimeter drain.

Details about interior perimeter drain systems are at PERIMETER DRAIN SYSTEMS

French drain sketch (C) Daniel Friedman

Watch out: the sketch above shows what can be a common and serious mistake: connecting the roof drainage system or downspouts or leaders into the footing drain system.

The result is likely to overload the footing drain or even if it doesn't do so right away, eventually the footing drain clogs and the roof drainage ends up in the building basement or crawl space.

If you have this bad arrangement at your property you should consider a temporary above-ground extension to the downspout - don't leave it emptying into the foundation drain system.

Building Footing Drain Details

Find the end of the footing drain system that used to drain to daylight (see our photo below).

The foundation drain system may have become buried with mud or covered by backfill. Clear any blockage at the end of the footing drain extension, open and check the end for water flow in wet weather.

Footing drain to daylight (C) Daniel Friedman

Clogged Footing Drains

Even if foundation drainage was properly installed when a building was constructed, the system may no longer be working. Over time fine soil particles can enter and clog the foundation drainage system.

If you know that a foundation drain system was installed - perhaps you can find the end of it as we illustrate above - and if the building foundation is leaking water from low on the foundation walls, and if little or no water is coming out of the end of the footing drain in wet weather, it's a good bet that the drain system has clogged.

Our photo (below left) shows the footing drain that was excavated and removed at the home of a client whose house suffered recurrent flooding. The old footing drain was totally impacted with mud.

Clogged footing drain (C) Daniel Friedman

The photo below shows the ends of three new footing drains that were installed and carried to daylight. We remained a little nervous about just what the builder used for backfill - notice that silty mud coming out of the new drains? They may not have a long life.

Clogged footing drain (C) Daniel Friedman

Foundation Drainage Backfill Details to Prevent Basement Water Leaks

Footing drain sketch(C) D Friedman

Foundation Drain Perforated Pipe Holes "Up" versus "Holes "Down"?

The foundation drain or "footing drain" I show in various illustrations above is a modification of the original page top drawing to illustrate water inside the drain pipe (blue) and the placement of the pipe with perforations "up". There is some argument among builders about whether or not the footing drain should go "holes-up" or "holes down".

Footing drain sketch(C) D Friedman

The "Up" position is thought to reduce the rate of soil clogging but has the disadvantage that water outside the foundation has to rise to the height of the holes to get into the drain. This isn't a terrible problem for the common case that water is entering the footing drain by percolating down through soil from above.

Still in my OPINION "holes down" and well bedded in gravel under as well as around and above the footing drain pipe and with gravel covered by a geotextile is the optimum solution. That means water finds its way into the footing drain system as soon as it reaches the level of the bottom of the footing drain pipe - sooner than if it has to rise several inches higher to get into the drain line. That reduces water pressure under and around the foundation footing and reduces chances of water entry into the structure.

Incidentally though I show blue in the bottom of the footing drain in the sketches above, you should not normally see standing water in a footing drain. If you do the drain is

  1. Partly or fully clogged
  2. Not properly sloped down to daylight
  3. or is overloaded and inadequate to handle the volume of water entering the drain system - you might see this condition of you examine the footing drain interior during very wet weather and during heavy rain.

We discuss the orientation of perforated drain line holes - up, down, or in-between, in more detail and in a different application at SEPTIC TRENCH LINE SPECIFICATIONS.

There where we are worried about sewage sludge clogging the drain system we put the perforated holes at 5 and 7 o-clock if we can, theorizing that we're deferring the clogging of the drain line exit holes by sewage sludge. You could make the same argument about silt collecting inside the footing drains around a foundation.

But for foundation drains around a foundation, I'm more worried about intercepting water as soon as possible to keep it out of the building.

Overloaded Footing Drains

We explain at GUTTERS & DOWNSPOUTS that it's a bad idea to connect the roof drainage system to the building footing drains. The added water volume may overload the drain system leading to foundation leaks.

And worse, when later in the life of the building the foundation drains clog, we suddenly begin directing 100% of the roof runoff into a lake of water trapped around the building foundation - virtually guaranteeing that the basement floods.

Our photos (below) show a home whose roof drainage system passed through the crawl space wall, across to the other end of the building, exited the crawl space to go back outside where it dove down into the building footing drain system. The result was a constant wet finished basement.

Notice in our second photo (below right) that a clue telling us the whole drainage system was clogged and backing up was that during rain water leaked out of the tee at the top of the vertical drain line that was connected to the footing drains.

Clogged footing drain (C) Daniel Friedman Clogged footing drain (C) Daniel Friedman

At a recently constructed home we determined that the roof gutter system was connected to the foundation drains, and warned the buyer about the chances of basement flooding. The home was ten years old, and the basement, by every inside inspection indication, was "dry".

But two years later, following a period of heavy rain the client called to exclaim "Geez, our basement is full of water!" IT was like throwing a switch. The footing drain outlet clogged and the basement just filled right up.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.


Continue reading at BASEMENT WATERPROOFING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see FOUNDATION DRAINAGE FAQs questions & answers about foundation drainage systems

Or see GRADING, DRAINAGE & SITE WORK for a description of exterior surface grading and runoff control

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