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French drain around house

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  1. #1
    Apprentice (new member)
    Join Date
    Mar 2011

    Default French drain around house


    My house sits on a cut-out block. Half the house is on a concrete slab and the other half is up in the air on brick pillars. between the slab and the pillars is a 2 metre vertical retaining wall. This area under the kids bedrooms has been enclosed and is use for storage. I could use these rooms as an office or gym if it wasn't for ground water seeping when ever it rains. And there is the problem. When it rains the rooms under the house get wet or flooded (puddle). Looks like there is no drainage behind the retaining wall and the soil around the house is clay and shale. The dampness is also causing mold to grow and I am afraid mold spores are getting into the kids rooms and making them sick.

    I tried to dig a french drain around the top concrete slab but it was too difficult to do it with pick and shovel. I contracted a excavation contractor only to find out that directly under where i wanted to did the trench are the house sewerage pipes. I did break a pipe but i managed to fix it.

    So here is the story. To did the frnech drain i need to remove the sewerge, dig a deep 2 metre trench down the side of the house in a limited access area. Then install the slotted pipe, waterproof the downhill side of the trench, add the clean river rock, re-install new sewer pipe and finish off the trench with more rock and re-tile the area.

    I got a couple of quotes and the seem very $$$. It's basically a 10 metre trench. Access is limited to 1 metre width with no room to turn an escavtor. Meaning all soil needs to be removed by wheel barrow. Once the trench is dug the rest seems easy.

    Does anyone have advice? Or experience with a similar situation. I would ideally like to find a contractor with such experience who could provide a detailed quote, other than saying X amount of dollars for the Job.

    thank you.

  2. #2
    Senior Member
    Join Date
    Jan 2011


    The french drain would be the ultimate but i was wondering if you could stop the water at the retaining wall. Bit surprised that such a retaining wall was built without drainage. Have you checked on that with the original builder or Council? If the water is coming through the retaining wall a company called Gripset have a product that you can apply to the face of the wall to stop the penetration. They have a free design and estimating service. If the water is seeping under the retaining wall can you put the french drain in front of the retaining wall and remove the water before it gets to your lower level rooms? It may be worth talking to a structural engineering firm for advice.
    If you can collect the seepage and remove it, install a new rear wall to your lower level. the space between the retaining wall and the new rear wall will need some cross flow ventilation happening across this area, vent one side extraction fan the other. this will help remove any wet moist air from the sub floor area and prevent that mould built up.
    Good luck

  3. #3
    Apprentice (new member)
    Join Date
    Mar 2011


    Thank you Hoppy.

    I shall investigate whether the wall has any drainage. I suspect another retaining wall to the rear of the main wall may be blocking drainage. Lets hope it does have drainage. who save me some money. I'll let you know the out come.



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