Foundation Waterproofing Basics: Exterior Drain Tile


Foundation Waterproofing Basics: Exterior Drain Tile

Whereas interior drain tile is sort of the jack-of-all-trades of the basement waterproofing business, exterior drain tile does one thing and does it extremely well – intercepts and drains away ground water before it can get into your basement.

As part of a system of “positive side” waterproofing, exterior drain tile protects your basement no matter what the source of ground water: absorption of heavy rains, overflowing gutters, misplaced downspouts, even over-watering of plants and shrubs. 

What is Exterior Drain Tile?

Exterior drain tile may be known by different names depending on your location – it’s “French drain” in the eastern U.S., “weeping tile” in Canada, “footing tile” in many places and maybe has a different name where you live.  Whatever you call it, it does the same thing and is installed the same way.

To begin, we dig.  A trench must be dug around the entire foundation down to the footings.  It will be as narrow as safely possible but also requires room to store the excavated soil so the entire process takes up quite a bit of space on the outside of the home.

Next, a bed of washed gravel is laid in the bottom of the trench.  Perforated PVC drain pipe, wrapped in a “sock” of filtration fabric, is then installed next to the footings in a continuous loop around the foundation, draining into a sump basin where it will be discharged outside the house by a sump pump.

More washed gravel is added on top of the pipe to promote drainage and the trench is backfilled.

When exterior drain tile is to be installed, a basement waterproofing company will also install something to protect against seepage through the foundation wall; doing it later would increase the cost substantially.  The best practice is to apply a waterproofing membrane to the outside of the wall and cover it with drainage board.

A heavy coat of the membrane, an asphalt-modified polyurethane material, can be troweled orExterior waterproofing membrane sprayed on to seal the foundation wall against water from the outside.  This is particularly good for cement block or other masonry foundations.  Drainage board, a heavy plastic panel with molded dimples, protects the membrane and channels water down to the drain tile.  It can also help ease lateral pressure against the foundation.

Why Would I Install Exterior Drain Tile Instead of Interior Drain Tile?

There are several reasons, although the ultimate in basement waterproofing would be to have both, since each has a slightly different purpose.

Preserve the Foundation Wall – When water seeps through a porous foundation wall, it causes damage and deterioration to the wall that may lead to serious foundation problems.  Exterior drain tile drains that water away from the soil surrounding the foundation so that it never permeates the wall.

Masonry Foundation – If your home sits on a foundation made of concrete block, brick, stone or other masonry, exterior drain tile can prevent major problems.  Because all masonry materials are held together with mortar, there are joints in masonry walls that are prime points for leaks because the mortar is more permeable than the block, stone or brick.  As above, exterior drain tile will prevent ground water from seeping through and causing wetness or structural damage.

Finished Basement – If you’ve already poured your time and money into turning your basement into beautiful living space, you won’t want to tear it apart to do interior drain tile.  In fact, unless you have landscaping right next to the foundation, which is never a good idea, there will be very little for you to do to get ready for installing exterior drain tile.  Except for the sump pump connection, the work can be done without access to the interior of your home.

Is exterior drain tile the best thing for your home?  Maybe.  At U.S. Waterproofing, we’ve installed thousands of exterior drain tile systems in our 55 years in business and our trained basement advisors can help you determine the right way to keep your basement dry.  Why not take advantage of our free advice?


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