French or field drains, plus suitable pipework

[friend of stouby]

hope this is ok but have posted this on an older thread but it didn't appear to work, so have started a new thread here

Had a look at quite a few websites re field drains recently and most were advocating using solid pipe with holes only at the bottom rather than the flexible convoluted pipe as the ridges create friction to water flow. Was in a Big Mat and took the oportunity to look at the field drain pipework and was surprised at how thin the wall of the rigid pipe was ( this is the pipe used for fosse septiques ) the convoluted pipe was also semi flexible.

The question is, is there another type of solid field drain pipe that is used only for field drains but with a thicker wall thickness, maybe a similar thickness to standard drainage pipes, or in France is the fosse septique pipe used for all these applications. I don't want to use the old style ceramic or clay pipes but prefer to work in plastic.

I need to install a field drain behind our house across the uphill slope, and a local builder has mentioned that the drain must have the depth of the rear wall foundations. The drain will be dug about 5m uphill of the rear wall and will need to go to a depth of approximately 1.2m, so therefore quite a weight of gravillion ?(spelling) above the pipe, and it occurrs that the pipe may be crushed?

Thanks in advance to anyone who has any experience of this depth of field drain.

Jamie

[virginia.c]

jamie

whilst this isn't the reply you want I'm afraid, your question is very pertinent to a problem I have at the moment.   I am about to purchase a house where the side wall is built into a slope to the height of the ceiling of the ground floor.  Water is seeping through the side wall and under the floor.  We haven't yet had chance to find a local builder for his advice but we have been thinking that we will have to dig down to the foundations, expose the side wall, insert proper drainage along the wall and back fill with gravel etc.  Another complication is that the boundary is at this wall so we will have to ask the adjacent property owner for permission to go on to his land to dig (with a JCB).  When you say that a builder has advised you to go 5m uphill from your property, this concerns me.  Is the problem you are trying to correct similar to mine or are you trying to prevent something similar occurring?  I also wonder why you have to go 5m behind rather than nearer to the rear wall foundations?  We have a structural engineer visiting the property this morning.  He is looking specifically at the damp/water problem as well as roof etc.  If he comes back with anything pertinent I'll let you know.  Perhaps you could let me know if your reasons for the field drain are similar to mine?

thanks and hope you get some replies which answer your questions, rather than asking you more!

[friend of stouby]

Hello virginia.c

The advice from the builder was to dig the trench to the same depth of the footings, and obviously the further up the hill the trench is dug the deeper the trench. The reason for the 5 meter behind the rear wall was down to us as we will in around 2 years have an extension bulit across the rear of the house and therefore to allow clearance for this.

One piece of advice from a UK website re French Drains near to old buildings with no or shallow footings, was that the trench is dug away from the wall at a 45o  angle to allow for support to remain under the the existing footings, and that 1m away from the wall would be better/ideal.

I am not an expert but prefer to ask/research a job before tackling it and with all the info available make I hope the correct decisions. We currently have a soil/ballast/rubble mix against the rear wall to a depth of 1m. The walls are only ever damp inside after extreme weather so this mixture does work to an extent. We may have a spring that runs from one position at the rear to the front of the house, but until it is excavated we are not sure on this. The front and rear wall at these points have a little cracking plus a couple of floor tiles have cracked in the same area. I have read that it was fairly common for drainage channels to run from the rear to the front of buildings under the floor and this may also be a conduit for ground water to run under the house.

After excavating against the rear wall I'm sure we will know more detail, and then the plan is to remove all soil against the rear wall down to a depth of just above the footings. Then dig the drain trench to channel the surface and sub surface water running down hill away from the house. The expectation is for the wall to remain drier but not dried out, and for the possible flow of sub surface water running under the house to be either stopped or greatly reduced.

Last, when we returned to the house after a month or two away, the house smelt a little damp and in places felt it. We now use a large wood burner to create a superb air change when we are at home and have fitted simple ventilation ducts to front and rear walls to help maintain ventilation when the stove isn't lit. These two features have made a massive difference to the humidity in the walls and floors, plus have created fresher and drier atmosphere inside the house.

I don't know if any of the above is of help but do hope there is something there for you. The reasoning for the drain is to simply prevent surface and sub surface water reaching the building either at all, or greatly reducing it. The logic is that if water doesn't make contact with the building on most of the surfaces it will not be as damp, and usually French Drains are easy to install, and I try to always keep it simple! 

There are of course other factors involved in this and if you want to ask other questions please do so either through here or with a pm. I'm very interested to hear of anything that you come up with and on which direction you will take. Hope it all works out for you and that it gives you as much pleasure owning a French home as it does us.

Jamie