French Drain or Freedom Drain

I just had an opportunity to inspect a basement that was swimming in water. After chatting with the home owner I discovered that they had paid a contractor last summer several thousand dollars to install a French drain around the foundation with an assurance that this would fix the leaky basement. Firstly, a French drain is not something invented in France. It is a drainage system invented by Henry French in Massachusetts in the mid 1800's as a way to redirect surface and subsurface water from valuable farm land. Secondly, it is not a waterproofing system just a moisture redirection system.

Modern Basic French Drain

This diagram is essentially what a French Drain cross-section should look like. There are a few variations like PVC liner and clay lining that will improve the efficacy along with a landscape fabric cover/filter on the pipe with diminishing sized gravels above the fabric liner to decrease clogging. The end design will be determined by what you need the drain to do. If it is removing surface water from a marshy section of your yard then a broad shallow drain a few inches under the surface may do the trick. If it is removing surface and subsurface water from near an 8 foot deep basement wall then the method is more in depth, similar to the I come across contractors and hacks all the time who speak as though the "French" drain is the solution for all water penetration issues, most don't really know what a French drain is. Most of the drainage systems I have seen are some personalized version of a gravel drain or a form of collector drain that the creator calls a "French" drain. That said, some of these are exceptional pieces of work, I have seen some that deserve their own name. However, I have seen some, most really, that are truly just a hack job. They don't do the job that the creator proclaimed they would do when selling the idea to the client. What is truly shocking is some of the online advice and YouTube videos from so called drainage specialist who just dig a trench, throw in some gravel and a perforated pipe and call it good. Such a system will block quickly, in just a few months in some situations.

This perforated pipe was not adequately protected and dirt, silt and roots blocked in a short period.

The important things to remember with drainage are:
  1. Water will find its way in if there is a way in.
  2. Water will take the path of least resistance.
  3. Water will pool at a low spot.
  4. Water will flow down hill.
With those things in mind you can look at most systems and you can see if it is going to work. Ask the following questions:
  1. Will it stop the water from coming in?
  2. Will it keep water out?
  3. Will it direct water away?
  4. Will the water flow downward?
  5. Will the water stay way?
With those factors in mind you should be able to tell if your contractors plan is really a potential solution for your problem, or just an expensive hack at the problem. In a previous post about drainage I refer to the proper conventions for "waterproofing" a foundation according to the International Residential Code 2003 (406.2) and such big names as Bob Vila. If you have a basement leak do some research and when the time comes hire a specialist or a very competent contractor and have a very clear conversation about how to tackle the problem. If your contractor has a solution that is a 2 foot deep French drain protecting your 8 foot deep basement wall then he probably doesn't know what he is doing. If he proposes a solution that incorporates a "French" Drain, some deep excavation and some sort of a foundation liner in the overall project scope then it is probably a good bet he knows what he is doing.

A liner and French drain installed correctly

The above pictures show the correct use of a French drain when "waterproofing" a foundation. This work appears to be deep enough to meet the water penetration levels of the basement/foundation, the liner is a combination of tar and plastic liner and it lines the base of the trench where the perforated pipe is laid. All that remains is to protect the pipe from clogging (several options) and back fill with gravel (also several options). What I like to do when possible is in the following diagram.

Ideal basement foundation waterproofing

I like to add the extra plastic liner on the top of the soil angled away from the foundation. It really diminishes surface water. By adding some soil or gravel or even a concrete walk way on top of this really reduces sub surface water and improves the efficacy of the whole system. Where possible try to make sure your surface plastic is black 6 mil plastic, this will reduce any plant growth trying to punch through the plastic. In some areas it is hard to find 6mil black plastic in which case use the clear plastic but top it off with 4 to 6 inches of topsoil or gravel, or best of all a concrete path. Good luck.  
This entry was posted in Best practice, Project Tips.

Post a Comment

Your email is never published nor shared. Required fields are marked *