# Forum Home Renovation Landscaping, Gardening & Outdoors  Trench drainage - french drain or backfill?

## nachozden

We recently discovered leaks into our finished basement. Not gushing water, but enough seeping in to cause mildew smell, mold on the back of drywall and rot some stud wall sill plates.  At first we thought it was a leaky foundation, so we demolished interior walls and excavated an 18" wide trench on the outside. We saw the primary issue was our next door neighbors yard, where he had soil and big bamboo plants against and above our foundation and against exposed wood (this is an old house). Holes from roots and rot allowed water in. These plants and soil have been removed. To keep the lower soil grade against our foundation, well maintain that trench between and build retaining wall on the other side of the trench to hold up the neighbors higher grade.  We got a professional opinion that there is no water entering through the foundation or floor, so, theoretically, problem solved. The question is - how we backfill the trench to encourage proper ongoing drainage? French drain, soil, gravel, rock, something else?  Attached are some pictures showing the situation. The plastic shown in the later two pictures is temporary covering for the exposed foundation, which is shown in the first picture.  Some contractors insist we need a $20K-$30K french drain system. Others say we can just waterproof the exterior foundation wall since we have access, then backfill the trench (both much less expensive).  It doesnt rain a lot here, except during winter, when every few years we get rain heavy enough cause sewer backups. In our case, water runs downhill alongside/parallel to our foundation, not towards. Roof gutter downspouts overhead are connected to city drain pipes. Soil is pretty packed with a lot of clay, but it does drain.  My thought is backfill that trench with the drainage gravel they use over French drain, and keep soil off of it. My concern with that is that water spilling down the hill and over retaining walls could overwhelm the trench, which would drain more quickly than the soil.

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## Bluesrule

I'm not an expert on this and rules in your area may be quite different to those where I am. 
A french drain system would be good but may not be required in your situation.  
If you need to direct any water from the trench to the city's storm water system then a proper french drain is required. If, however, you just need to direct the water away and it can then flow over your land (assuming you have the slope for this to occur) then you could just backfill the trench with gravel. In my situation I did use what you call a french drain then filled the trench with gravel and then used some larger river pebbles on top to make it a garden feature. Very easy to keep free of weeds and means that everything is very free draining. 
Your thought to backfill with drainage gravel will essentially work as a french drain except that you need to ensure that there is somewhere for the water to go in the event of a lot of rain - as I suggest above this will work well provided the water has somewhere to flow away. Just make sure that you are not creating a "hole" where water sits as this will create problems with your foundation.

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