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Last Update:  11/11/15
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Actually, there are at least two different kinds of drains that are called "french drains" - inside and outside.  Outside french drains are usually installed when the house is constructed, although they can also be installed on an existing structure.  Drainage pipes are installed next to the outside foundation and drained properly.  On existing buildings, the outside foundation backfill must be excavated and then drainage pipes installed, entailing more work, and the additional danger of damaging foundation walls.

The inside foundation is dug to the footings, and drainage pipes installed, which generally run to a sump and is pumped from the structure by a sump pump.  In most areas, sumps cannot be drained into your sewer system, they must be vented to the outside.  Most french drains are installed on the inside, as the cost is much less, and usually it is just as effective.  Inside french drains are installed both during construction, and afterwards.  Make sure your contractor is reliable, check with the BBB, for one, also talk with other friends and relatives who may have had the same problem.  Deal with established, experienced companies with a creditable history in that industry.


Here's a quickie picture tour of a waterproofing job one of my customers had done in her basement....
French drain picture tour


French drains work by curing a symptom, not the cause.  They extract the water collected in the drainage pipes to the outside.  There are many variables that affect how individual houses develop water problems, and most of the time it is these combinations of factors, with time being the most important.  Inside french drains are then used to channel this water away from the house.

If you build a house, be sure to ask the builder to include inside (and maybe) outside french drains on your new house.  They may not seem important now, but as your house ages, water incursions will change, over time, and a cheap installation now may relieve expensive headaches later.  During construction, the cost of a french drain is negligible.  Spring for it.  DEMAND it.


Post-construction french drains are known to sometimes exacerbate termite problems. Termite inspectors discover this problem routinely.  Termites will even build their mud shelter tubes directly out of the drain slot of french drains.  This can even happen after you follow all of the rules of putting in a french drain properly and informing your exterminator of the installation beforehand.  

The reason for this is that these post-construction installations are usually done on houses that have established moisture paths alongside the foundations.  Our New Jersey eastern subterranean termites follow and exploit these moisture paths, eventually winding up right near your newly-installed french drain.

When this happens, sometimes termite control procedures are not necessary. Sometimes other methods are in order, and might include physical barriers, or even baiting techniques.  Every case is different, and this is where you need the help of your exterminator.  He will be able to evaluate the situation and make his recommendations as to what should be done, if anything.  There is a distinct possibility that NOTHING should be done.  

And, if you are not under contract with an exterminator already, and have to have several exterminators stop in to see the problem to give you their opinion, and perhaps an estimate, expect several different treatment proposals and methods. Termite control is an expertise, not an exact science, so each exterminator will have his own way of doing things.

HINT:  Look for the guys that try to save you money instead of pumping up the job. Make sure you are talking with an exterminator, not a salesman.

When you finally decide to have a french drain installed, follow a few simple rules: Get a referral from someone you trust, that has had work done by that company.  MAKE SURE you check with your local office of the Better Business Bureau, they can tell you if they have any complaints on the company.  Ask the BBB for their own recommendations, many offices will now do that.  You might also check with your local realtor.  They deal with this problem all the time, and can often steer you in the right direction.  Call the same agent that was involved in the sale of your house.

Watch out for the french drain "salesman" - you will be paying their commissions, so it will be in their best interests to charge as much as possible.   Ask the person if HE will be the one on the job.  Get several estimates, as many as you feel comfortable with. Make sure you talk personally with the representative, face-to-face.  Don't have the contractor show up for the estimate and just deal with the kids, the maid or the babysitter, you'll get a higher price, guaranteed.  

In addition to the installation of the french drain, don't for get to pay attention to the other causes of water in your basement.  There are many waterproofing companies that will ignore an easily corrected gutter problem to propose a much more expensive french drain.  Improper gutters and gutter drainage COULD be the ONLY reason you are having water problems.  Naturally, the french drain would cure this problem, but proper gutters and arrangement might do it a lot cheaper.


Pick a nice RAINY day, grab the umbrella and go out and stand there, in the rain, where you can see what is happening with the water draining through your gutter system.  You might have to do this on several occasions, rain from other directions might be a different matter.

Okay, so there you are, standing in the rain, wondering if the neighbors can see you. Now take a look at THEIR houses, and THEIR gutter systems too.  (Try to be discreet.)  Take a walk in the rain with your umbrella, checking all the neighbor's houses, and shortly, you can easily get a feel for how gutter systems work, (it's not rocket science) and whether or not yours is working correctly.  If you have a BIG roof, (lots of area and drainage) you'll need lots of downspouts, plain and simple.

Don't forget the trees.  If you have lots of trees, you'll have lots of leaves.  And need to clean those gutters out on occasion.  Even if you install those gutter screens/guards/helmets, eventually you'll still have to clean them out, and you'll have to remove those screening devices - sometimes not easy!  At certain times of the year you could do this almost every two weeks.  Especially if you have big trees. Install gutters with this in mind, and request oversized gutters with plenty of downspouts and as few and shallow bends as possible.

Frequently, gutter installers will skimp on the downspouts because they can then quote a cheaper price to the homeowner, knowing that their brand new gutters are going to work better than the old ones, at least for awhile.  Most homeowners won't know or even bother to calculate the number and location of downspouts, so they often wind up going for the cheapest price.  After all, gutters are gutters, right?  Well, sorta - but only if they work as they're supposed to work.  If they're not designed and installed correctly, water will not be channeled away from the structure and will pool next to the foundation and eventually leak to the inside.  This is what a french drain corrects. Proper gutters will help your french drain work correctly and last longer.

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