Drainage Around House Built Into Hill

Old 07-24-14, 10:10 AM
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Drainage Around House Built Into Hill

I have a drainage issue at a house I recently bought and wanted to get feedback and advice on what to do. (Please let me know if this is the correct forum to post the question in).

The house was originally built in the 1700s into the side of a hill with natural ledge. This probably helped provide a natural foundation at the time. A slab foundation is currently installed. Various renovations have been done on the house. At some point tiered stone retaining walls were installed in the back to provide a larger yard area at the top as well as a terraced garden.

The problem I am having is moisture at the back of the house (the first floor is below ground level). I don't know if the back wall was ever properly sealed or if the slab was sealed or if there is drainage around the base of the slab. It would cost too much to excavate the backside of the house since the whole hill would need to be held back during the work so I'm going to rule that out.

All I can control is surface drainage. The roofs all have covered gutters leading to downspouts that are piped to the street in solid 4" PVC so that solves the roof. What I'm trying to figure out is how to direct the runoff from surface water at the back.

I'm assuming any sort of traditional drain with crush rock against the back would be a bad idea since its inviting the water in and I cannot get deep enough to have the drainage go below the slab. What I'm thinking about is the following two-pronged approach:

1. putting french drains in back of each of the retaining walls to divert water away before it reaches the house.

2. Installing a surface channel drain slopping from the center away on each side and resealing the concrete.


Overall the moisture issue isn't too bad unless it rains so I'm thinking most of this is coming from the top down and not from below the foundation. So if I can solve the surface water issue and get a powerful dehumidifier for the first floor I should be better off. Ideally I could get the whole back wall clear and see what is there but that isn't realistic given the ledge and retaining wall issues.

Here is a link to the pdf I made detailing the issue visually:

Drainage.pdf - DocDroid

Any suggestions would be much appreciated. Please let me know higher budget suggestions too. I can always try and bandaid it now and solve it permanently down the road.

Old 07-24-14, 04:04 PM
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It's a problem if you can't dig. That's usually the best solution. The trench drain that you posted might be a good idea but it has to be way bigger than that one. A dehumidifier isn't going to do much.

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