Questions about french drain

What is the correct design for a french drain, should there be a layer of filter for fine particles, e.g. a layer of weed fabric around the pipes or outside the pebbles? This drainage system would eventually clog up, right (all filters clog up eventually). Also, how do you prevent plant roots from entering and damaging this drainage? Do I have to rebuild the french drain every few years?
It is alot easier to build this french drain if I can drain the water out the sidewalk (which eventually drain into the sewage) instead of directing it into the sewage. Is there a code against this?
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peter wrote:

Andy writes: If you do a www.google.com search on "french drains", you will find dozens of hits from various do it yourself places that explain, detail,and instruct on every aspect of french drains, including several ways of doing it....
French drains last a long time. The methods used depend on the soil they are in. They can drain anywhere you want, but if your sidewalk has several inches of water on it from your drains, you are likely to make somebody complain... Pay attention to the size of the trench.
Andy
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Yes do the google search. Basically you need gravel of the right size, perforated hose, and fabric to separate dirt from drain system so it doesn't fill with mud.

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Talk to your city code dept. Drain tiles have worked for hundreds of years done right. You may need Little
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The problem with doing a "Goggle" search is the fact that you will get thousands of hits ranging from absolutely uneducated to somewhat good. Advice from "experts" is also variable and sometimes unreliable. I've done a fair amount of research on the subject and consider the following book to be one of the best:
Practical Drainage for Golf, Sportsturf and Horticulture
This is a $50 book, but it is available from any reasonable-sized library system. The authors discusses many of the misconceptions of drainage systems, such as the historical advice that course gravel (or any gravel) is the optimal fill material. The authors are British and have analyzed the failures of many extremely expense professional drainage systems which were installed using conventional wisdom. Many school fields, golf courses, and soccer fields have had "professional" drainage systems that were major failures.
I became a believer when I saw several friends install "conventional" French drainage systems which turned out to be such major failures. It should be noted that the same systems installed on different terrain, different soil composition and different grades may have turned out to be excellent systems.
The book is about 200 pages and goes into a lot of the science and engineering aspects of soil structure, water retention, capillary action, capillary fringe, perched water tables, subsoil particle movement (especially through course gravels), etc. While it is a bit technical at times, it is still presented in a manner that the average layman should follow easily. It should be fairly easy to do a first reading of the book in an evening, although you are obviously going to want to go back and re-read portions at a later time.
You can install a system the "brute force" method and avoid doing significant research - guessing at intervals between trenches, trench depth, fill material and so on. The system may work 50% of the time or more, but is it worth the risk of investing so much time and materials and winding up with a system which performs very poorly?
FYI: The authors generally suggest course washed river sand as the fill material rather than gravel. This is discussed in detail.
FYI: Zoning codes are not universal. We can guess about whether your system must be discharged "to daylight" or can be tied into a storm (not sewage) system, but a quick phone call to your local zoning folks will get you the correct answer rather than random guesses from us.
You mentioned sidewalks, which implies that you live in an urban area with sidewalks and curbs. If you are going to discharge through a curb cut, then this can present challenges at times depending upon the pitch of your property toward the curb. Your curb cut is going to be just a few inches below grade, whereas your drainage system is going to be deeper than that. If you don't have sufficient grade running down toward the curb, then you may have a dip in your system which can fill with any fine particles which enter your system and should normally stay in suspension and flush from the system.
Some localities will allow a tie-in to a subsurface drainage system, but never into a sanitary system. A direct tie-in to the storm sewer system is optimal, but may be not be allowed or may prove to be rather expensive.
Often, a tie-in to the gravel drainage base below your street surface may be permitted for sump pump discharge, which has relatively clean water, but not for field drainage systems, which may carry fine particles into the street's gravel base and diminish its drainage capacity. Even for sump pump discharge, most municipalities prefer discharge directly into the curb except for extenuating circumstances such as considerable winter street ice caused by sump pump discharge into the street.
Gideon
====================== peter wrote in message ... What is the correct design for a french drain, should there be a layer of filter for fine particles, e.g. a layer of weed fabric around the pipes or outside the pebbles? This drainage system would eventually clog up, right (all filters clog up eventually). Also, how do you prevent plant roots from entering and damaging this drainage? Do I have to rebuild the french drain every few years?
It is alot easier to build this french drain if I can drain the water out the sidewalk (which eventually drain into the sewage) instead of directing it into the sewage. Is there a code against this?
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