House at the bottom of a hill - Drainage help?

11 Replies

Hi, I own a house which is situated at the bottom of a large hill. The house itself is fine, but the garage sits back further than the house so that the back of the garage is only about 5 feet from the bottom of the hill. This 5 feet of space is consistently mud, and it gets so wet that in the winter (rainy season) water runs through my garage quite severely (there is a constant stream through it).

I know very little about drainage. How should I fix this? Due to the neighbors garage being 6 inches from my garage on one side, and my house on the other, I cannot just dig a ditch for the water to run.

Would digging down a few feet, then filling the area in with gravel help? Or installing a sump pump? and how would I do that?

Any ideas or suggestions would be great. My tenants would love to use their garage floor again :)

Your problems are likely more than you realize. By your description, the water level gets higher than the concrete slab. If this has been happening for years you've probably got a rotted sill, which is the where the wood sits on the concrete.

The wood will wick up water above the water line, inside the wall and you'll get rot and mold in and on the walls.

I'm going to guess that over the years, erosion from the hill has left the ground level behind the garage higher than the slab elevation, and you've probably got a negative grade, meaning the dirt from the hill slopes to the garage, not away from the garage. You could try to remove enough dirt from behind the garage to create a downward slope away from the garage to the bottom of the hill, making sure you've got several inches of the slab exposed. Might be a lot of dirt, and you might want to consider installing a low retaining wall along the hill to prevent future erosion.

Create a shallow ditch at the base of the hill, at the bottom of the grade coming away from the garage, creating a channel for the water, sloped to either or both sides of the garage. It sounds like enough water comes down the hill that you'll need some type of drainage. If you can't channel the water around the garage, you may have to install a drainage pipe, given that you've got a downhill destination for the pipe.

Don't recall the recommended slopes for a positive grade against a building, something like 1 inch every 4 feet, or for a drain pipe, something like 1/8th inch every 4 feet, but these should be easy to find.

Also, if the roof of the garage contributes any water at all, install gutters. If your garage and your neighbors garage, or your house are close to gether, and the roofs slope towards each other, you could be getting a lot of the water simply from roof runoff. If there are gutters, make sure the downspouts are at the front of the garage.

I wouldn't suggest any type of outside sump pump unless you absolutely cannot find a way to let gravity move the water.

Otherwise, when you sell the property, advertise an indoor water feature. :D

I wonder if a --what's it called--a dry well?--might be used along with your suggestions. Basically a large hole in the ground to contain the water so that is drains out slowly under ground via a drainage field, rather than sitting on top of the ground making mud.

Another option might be a cistern to gather and use the rainwater in your house, rather than city water.
You would have to take steps to keep it free of mosquitoes and debris, and filter it going in and maybe coming into your house for drinking (ultraviolet light system).
Something to think about.

Collecting rainwater for use in your house or garden is illegal here in CO, and I suspect it is in AZ, too. Might seem like raindrops that fall on your roof would be yours, but here in the arid west, each and every one belongs to someone. Might be OK, in WA, though.

I'd suggest getting a foundation contractor out to have a look. In a case like this its much easier to come up with a solution if you can actually see what's going on. Look for contractors that advertise drying out your basements. They should give estimates for free. Even just having them point out what's wrong and what they would do may give you some ideas about an easy fix.

deleted because of repeated post

What happened to the other one? Jon, you have got a QWIK set of fingers!

Lets try that again!
Water harvesting, both rainwater and gray water, is legal and encouraged here in AZ, and I'd do it with both, but I plan to move in a couple of years, and don't want to spend the money on this house.
Here's a blog with links re harvesting that others everywhere might find helpful or at least interesting.

I would consider installing a french drain. It's nothing more than a metal or plastic box 18" square with a 2" or 3" hole off the side. The top is a grate. You can then plumb PVC from the 2" outlet off the box to the drainage ditch around the garage/home.

I had a similar issue on my first rental. I had a french drain installed and the contractors were able to get a variance from the Drain Commissioner to connect the french drain right into the storm sewer. It worked out very well and I never had another issue.

Drain Commissioner.

Oh, I want that on my resume! :lol:

The water has to have some place to go. It you are the lowest point in the neighborhood, you might have an unsolvable problem. If you can get the water to the street and it has some place to go from there, maybe you can fix it.

How is the water getting inside the garage? If it is running down the drive and through the doorway, all you need to do is to put a diverter at the doorway-- sort of a speed bump for water.

If it is coming over the stemwall, you can try directing the water by grading. But if you are the lowest point in the neighborhood, maybe your only solution is to jack the garage up and make the stem wall taller, and then either add more concrete to raise the level of the floor, or add gravel to keep your stuff out of the water.

Your best bet is to have an engineer look at it. From here on the other side of the internet the best you can get from people who can't see the garage is a shrug and a "maybe"

Totally agree with P NW. Get an engineer. Trust me, lot drainage is not a simple science as there are so many factors to consider, plus it is of critical importance to the foundation of your garage and home.

Engineers aren't cheap, so if you want to save some money you might think about a landscaper. However, some landscapers are good with drainage, but most just think they are so if you decide to go with a landscaper, check their drainage references throughly. In any event doing it wrong can lead to expensive consequences, so definitely consult a professional.

My advice would be to hire the engineer and if you can handle implementing their recommendations, then do it, but it's best to let a professional prescribe the solution.

One more thing to think about is that it is probably not OK to divert the water so that it flows onto a neighbor's property.

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