I'm buying my first house very shortly, and as expected it has some problems. One of the big ones is water management around the garage. There is already water damage inside the garage so I want to tackle this as soon as I take possession of the house, but since I haven't yet all of the numbers below are eyeballed.

The garage is freestanding, with no gutters. To the left of the garage and behind it, there is roughly level ground for about a foot all around, before sharply climbing at a slope of probably 50+ degrees. The slope begins towards the front of the garage, but by the back of the garage it's about 3' tall. To the left of the garage, the top of the slope is almost right at the edge of the property, where the neighbor has a fence.

Here's a quick Sketchup to illustrate, because I'm sure that's as clear as mud.

Here's a quick Sketchup to illustrate

The previous owner had filled that trench in between the slope and the garage with sandbags in a failed attempt to keep the water out.

What I'm thinking about doing is constructing a retaining wall to clean up that slope and hopefully gain me a few inches, and then run a curtain drain (or French drain, there seems to be some terminology disagreement here) along the side of the garage, sloping towards the front of the property, and draining into a narrow bioswale or similar in between my driveway and the neighbor's property. I would also like to install gutters, and pipe the downspout on the left side down into the curtain drain.

In the back there's a good bit more space, but that hill runs the entire width of the property.

enter image description here

Here I'm at kind of a loss. My inspector recommended constructing a ditch that ran behind the garage and then down the contour, directing the water to the right of the garage. That would dump the runoff pretty much right where I was planning on making a garden, which is less than desirable. I had considered constructing a swale on contour instead to hold the water and encourage infiltration, but my understanding is that would be detrimental to the retaining wall I want to build to prevent erosion and for aesthetic reasons.

Is this feasible to pull off in such a tight spot? Would it actually work? Do you have any better ideas? What additional things should I consider?

  • type of soil? how much snow and more importantly, how long a period in the spring when the ground is frozen but air temperatures are warm? what is growing on the slopes next to the garage now?
    – kevinskio
    Apr 9 '17 at 20:23
  • I'm not sure about the soil yet. It looked sandy and hard to me, but the geological survey says it should have McHenry silt loam We're in southern Wisconsin. We get really weird springs that bounce all around, but I'd say a few weeks. Currently there's a somewhat sparse grass growing over the entire area, including the slopes. It's a cool season grass with broad flat leaves. I'm thinking it's probably Kentucky Bluegrass.
    – TBridges42
    Apr 9 '17 at 22:37
  • Average annual snow fall is about 50 inches, but with a very wide distribution curve. Some years we barely get any, sometimes we get a couple of feet at once.
    – TBridges42
    Apr 9 '17 at 22:39

Super question, T.! And I am so impressed you've got an inspector and have not purchased this home yet. This is a great way to get a better deal AND get the owner who is very interested to sell to FIX THIS before you have to deal with, well, truly a deal breaker. Did your inspector look at the supporting lumber for dry rot? Wet rot, grins? This garage, if you are able to see water damage and they've gone as far to put up SAND bags says this is a major problem and you might end up NOT having your detached garage at all even though that is part of the purchase price.

Your computer sketches are fascinating...you actually have included slopes! I need to know more for a better answer such as the material around the foundation of your garage, certainly soil type, what is the damage YOU are able to see, is that inspector someone who works on your behalf or the banks, or the real estate agent or the previous owners?

How did you get the slopes? Are these slope percentages accurate? And most importantly how much room do you have to play with to fix this OBVIOUS problem, such as property lines, distance between hard surfaces?

Grins, I taught this stuff BEFORE the internet, okay? Kinda shows my age but regardless I know how to do this stuff by hand as well as by shovel. You actually said SWALE!! I adore you! The ideal situation is being able to slope every bit of soil or hardscape AWAY from the foundation. Walls just do not work. Water has to hit the ground and instantly be directed AWAY from the building/foundation. Best scenario would be to create a swale at least 3' wide, a foot deep at least 2 feet and that is a stretch, of sloped soil/hardscape at a 5% slope away from the foundation. Less slope allows water to seep in through cracks and then we need to discuss your foundation drain system.

This swale not only directs the water away from the foundation but allows the water to start percolating back into the soil. It should be grassy from what I am seeing as your slope or your swale might need 'speed bumps' to slow the water so there is no erosion.

French drains are great but you have to have a slope away from the foundation, allowing no water at all to get near your foundation. A swale is far better than the french drain. But you have to have the room. I am only giving you bare minimum sizes and I expect that your space is limited other wise any sane person would have done something other than sand bags!+

Need to know the depth of the foundation, whether there IS a foundation drain system and asphalt emulsion on the outside of this foundation...for you to be able to easily see water damage and the sand bag thing is very scary!

To create a surface concrete run would be next, sort of what I see in your picture. This is conditional based on the neighboring properties grade versus your grades! This can be done...yes it can at some expense. Not that bad but my biggest worry is the condition of the structure having obviously endured a long time compromised by water./

If this inspector is not hired by you, hire your own. To thoroughly go through the home and its foundation as well. These private home inspectors are worth every penny!! And it has to be YOUR home inspector...and in my experience totally affordable and I would never ever purchase a home without one even though I've built 29 custom homes as a custom home contractor, owned 6 and have seen horrible stuff that the real estate agent should have known. Well, now those same agents have had lessons in order to keep their license and mitigate their reputation.

If this home is still a great buy WITHOUT the garage then heck, put more money into your research. If this garage is toast, look at the home next and do NOT put any more money down. Make the owner and/or real estate agent do some work. They have no compunction selling to ignorant buyers but buyers are protected.

Where are you on this planet?

Water damage is a very big deal. It is known as a deal breaker and I am so happy that you are concerned and actively researching this aside from any emotional attachment...first home? My goodness, you are rare! More information please...want to help!!

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