French Drains in Cold Climates 6

[minor4326]

I have a concern that my newly installed french drain will get damaged by winter thaw and freeze cycles. My house downspouts are connected to a French drain and I've got concerns that the snow/ice in the gutters will cause problems in the French drain during winter. I live in SE Michigan. Do I need to be concerned?

 

[BigH]

Why do you think you may have damage? - and what do you think the damage would be? How deep is your "French" drain?

 

[BigH]

Oh, and what material forms your French drain?

 

[civilman72]

If your downspouts are connected to the foundation drain, that will probably be an issue.

Can you see the outlet point of the drain? This is where you will probably have the most maintenance, but is better than having it buried.

 

[cvg]

roof drainage should not be directed to a "french" drain, but to a normal drain that outfalls to the surface and never connected to a foundation drain.

 

[oldestguy]

Any trees nearby? Will leaves get in the gutters? Once they accumulate in the drain, do you have a way to clean them out? In central Wisconsin my friends with this arrangement don't seem to have any trouble except with leaves. Of course it is possible to have frost depth go below the drain elevation and, during thaws, water from the roof may freeze there and stop up the flow, but with any depth of snow, that may be sufficient to insulate the drains.

 

[cvg]

rainfall runoff from a roof will usually far exceed the flow capacity of a gravel / sand perforated pipe "french drain" and during cold weather it is also possible that ice will form. If you want to dispose of the roof runoff water below ground, then discharge to a surface retention area where it can soak into the ground. with any sort of underground pipe drain, cleanouts should be installed to allow cleaning.

 

[emmgjld]

In my experience, dumping roof runoff into a foundation drain is very problematic, leading to overloading and possibly plugging the foundation drain media. You are also counting on the foundation drain being installed properly. My experience is that most foundation drains are moderately to severely compromised by both construction techniques and by improper assumptions (design & modeling). I personally am not a big fan of drains if other means can reasonably take care of the potential problem. But I realize that is just me and where I practice.

Following are my 'standard' recommendations (Colorado Foothills to Mountains) which may be appropriate to your original post:
... However, it should be noted that there is a considerable potential for seepage water on this site, particularly during wetter (snowmelt) seasons. Seepage can be expected to flow along the surface of the formational materials and in the fissures in the formational shale. It can also be expected in the upper colluvium in wet seasons. Seepage could be severe enough to present problems in construction, if construction is undertaken during wetter seasons. As a result of the seepage potential on this site, a subsurface peripheral drain system must be used for the structure. In is possible that two (2) levels of subsurface drains may be required. An upper, shallow drain may be required to protect against snow melt and poor surface drainage and a deeper drain at the foundation level to protect against deeper subsurface waters.

At the higher altitudes of this site, difficulty with freezing of drainage lines at the discharge point is probable. We recommend that this be overcome by discharging into a protected, coarse rock and cobble fill or mound. As an alternative, heat tapes can be used on the discharge point of the pipe. The drain outlet must also be located with due consideration given to the proposed pattern of snow storage and removal. Careful consideration must be given to snow plowing, plowed snow stockpiling and snow which will fall off/shoveled off the roofs (especially the northerly sides of the structure)as to preventing proper drainage of runoff away from the foundations areas, during the winter and the spring months.

 

[concretemasonry]

Around here, the generally accepted rule is to NEVER tie a roof drainage into the foundation drainage because the roof drainage is much greater (maybe 10x in short periods) and it can back up debris into the entire subsurface drainage and plug it up because foundation drainage is much slower and cannot flush the junk away. The roof drainage is ideally run in solid wall PVC to daylight, so it runs fast, free and away. The only possible problem is with a very cold early winter with no snow a shallow line may freeze for a while. Later(even with periodic -15F), with a good snow cover it will run better because of the snow insulation and natural ground heat down underground.

Ideally, the cheap flexible pipe (solid or perforated) is avoided because of places for dirt to accumulate and bellys cut the flow rate and capacity.

Every place has different minimum temperatures and timing of the cycles. I have seen ground frozen down only 6" with 18" of snow, but after a month of daily lows of -15F or much lower (-52F).

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[oldestguy]

I should add, the non-trouble guys have no trees and the drain is a solid pipe, no perforations. Outlet freezing does not seem to bother them, since it is under snow depth usually.

 

[minor4326]

thanks for all the wonderful responses. two more question before I answer some questions: about 600 SqFt of roof area will spill into my proposed French drain; how long do I need a 4" OD hose to absorb a very heavy rainfall? If I chose to discharge to a surface retention area where it can soak into the ground, what capacity is required?
- The "French" drain would be between 4-12 inches deep
- my downspouts would not be connected to the foundation drain - I want my downspouts connected to the French drain, totally separate from the foundation system. The whole point is to get water away from my foundation. It would be 4" OD black, 'plastic', flexible, perforated hose with a sock over it. It's sold at the big box stores. The end of the hose would dead-end in the ground. About 600 SqFt of roof would be diverted into this French drain hose.
- I plan to put 'leave guards' on the gutters where the flow is coming from

 

[cvg]

assuming 2 inches of rain will produce 100 cubic ft of water runoff from the roof. you need to store all of that or more depending on your desired design storm. do not use perf pipe close to the house

 

[civilman72]

Downspouts should be connected to a solid pipe, not perforated.

Bury the french drain as deep as possible. You will have freezing problems if only 4"-12" deep, unless your underground pipe grade is very steep.

 

[cvg]

if you can daylight the pipe to a low area, than there is no reason to use perf pipe at all and it would not be called a "french drain".

 

[oldestguy]

Minor:

I hope I am not interpreting incorrectly, but are you planning to take your roof water and run it into a 4" perforated black pipe with a sock on it? Then are hoping to have that water exfiltrate from the pipe into a trench filed with coarse rock (your French drain)? If so, it is an upside down design and would be a form of "dry well" in my area, but made wrong. The sock would trap a lot of stuff and eventually plug and then nothing would work.

Leaf guards are not perfect and let a lot of stuff thru and even plug themselves in some cases..

Clarify if I am wrong.

 

[minor4326]

Thanks for all the feedback. Let me clarify my proposed project. I am proposing to run rain water from my roof of approx. 600 SqFt, through the existing gutter/downspout, into a solid 4" plastic hose(from the end of the down spout five feet to the beginning of a French drain or ‘dry well’ system. The system consists of 4” OD perforated black plastic hose, covered with the appropriate “sock” material so dirt doesn’t clog the perforations, all laid in a bed of small rock. The hose would be ~60 feet, more if necessary, and dead head at the end. I want perforated hose so it will drain into the rock-filled trench as more water fills and dissipates the length of the hose. I live in southern Michigan with freeze-thaw cycles in the winter and my concern is the pipe/hose system getting damaged if the system is buried 6-10” deep, assuming the proper slope. Is this a concern? Does the length of the system need to be longer to accommodate a heavy rainfall? Thanks for your response.

 

[cvg]

unless your trench is very large, 60 feet of pipe will not come close to handling water from even a small rain

 

[civilman72]

If your pipe is only 6"-10" deep, you more than likely will have frost in this area for the majority of the winter. The snow on the roof may melt during a warm day but you will still have frost in the ground, so the melted snow water will not properly dissipate through the gravel media if it's still frozen.

As I said previously, I highly recommend you bury this pipe deeper. And agree with cvg that you need bigger/longer pipe.

 

[oldestguy]

Minor:

Ok, it will be a dry well. Forget the words French Drain. Agree, use perforated pipe. However, that sock is not needed, costs mre and is likely to plug. Water runs out and doesn't run in. It is water flow that carries along dirt and the direction is out.

The main info you need to provide is what type of soil is this going into? If it is clay soil, it may not work well or at all. This design should be the same as one would have for disposing of sewage water from a septic tank. If you really want it to work and need to figure sizes of dry well, check with a local Soil Tester, Sanitarian or similar profession who size waste water drain fields.

A crude way to figure size is to run an old fashioned infiltration test and do some calculations. Dig a hole to the depth you want (and the shallow depth you show looks not enuff) and set a ring, say a 5 gallon pail with the bottom cut out. Fill water inside it and outside it to same level always. (outside so your inside infiltration is only down, not sideways). Fill maybe 8 or 10 inches high. Let it soak for a few hours and keep inside and outside filled. Then (assuming a steady state), measure the drop in inches per hour. That can be done with a pointed measuring stick, against a board across the top. Then, that is a rough estimate of how well the dry well will work on a cubic foot per square foot of area for a given period of time, say one day. You might assume a rainfall of 3 or 4 inches per day for the extreme. An hourly rainfall of one inch could be used to figure volume of trench needed as a minimum. Don't forget the stone will take up maybe 65 percent or more of the total volume. To cut down on the length of trench, just make it wider. Play it safe and daylight the end of the pipe, even it it is up. Put a screen there to keep animals out.

However, keep in mind about freeing of ground. If the surface is not snow covered, frost depth can go well below 4 feet down in sand and gravel and a few feet in fat clay. If water table is close to surface, then this dry well method won't work very well.

 

[minor4326]

I have finally figured it out... I need to have a solid pipe that empties onto my lawn. Now that I figured that out, I have a concern about water draining during a winter thaw as a result of the sun, not higher temperatures. I need to put an extension onto the bottom of the downspout that will go under the sidewalk, then attach to a long underground pipe to carry the water away. I would bury the pipe about 6-10 inches deep, as it starts about 4" deep as a result of having to go under the sidewalk. My concern is freeze-thaw cycles during the winter. During a thaw caused by sun, not necessarily outside temperature, is water from the downspout going to damage the pipes at the bottom 90 degree junction in the ground, or anywhere else along the long route to the opening, due to the pipe being colder, probably below freezing. Am I going to have an ice jam anywhere? Is any damage going to happen by the draining water? I want to use the flex drain 4" irrigation hose. I'm sure schedule 40 would be better, but is it necessary?