I've been seeing water infiltration problems in my crawl space/open basement. The house is built on a cut & fill lot, with what I suspect is a sloped sandstone formation underneath the house.

Image of House Layout

I'm in California, where it doesn't rain often, but we've been having some massive storms recently, and this has been causing the basement to start filling up with water. As it's an open basement, this water infiltrates into my garage, and messes up drywall/finishings.

One of my options is to install a sump pump in the basement, but that doesn't seem like the best solution as that means water still gets under the house and potentially getting some of the wooden framing wet. In addition, I'm worried about the flow of water causing erosion of the soil under the house. I considered a surface french drain in the yard as well, but wasn't sure that would be at all effective.

I was wondering if anyone had any solutions that I could look into for controlling the flow of water into the house.

I've attached a diagram of the landscape.

  • If you want to first try draining the surface water collecting below the retaining wall, then create a swale parallel to the retaining wall, then a perpendicular swale around the end of the house to conduct this water downhill past the house. Another possibility is an underground "French" drain parallel to the retaining wall and then underground drain lines down grade past the house. If this gravity draining doesn't work, you might have to dig a series of shallow wells in a line parallel to the retaining wall and pump into lines going past the house. Jan 9, 2023 at 22:08
  • I was considering doing a french drain parallel to the retaining wall, about 2-3 feet deep, and about 2-3 feet from the foundation, draining into a sump which I would then pump out. But I was concerned that 2-3 feet would not be deep enough if the water was flowing deeper than that, and I wasn't willing to dig all the way down to the bedrock (expensive and messes with the soil integrity too much). Is there anything I could test to see if this solution would work without digging up my whole yard?
    – Dong Shi
    Jan 9, 2023 at 22:30
  • the area marked water filling up here is a crawl space? with a sloped floor? Jan 10, 2023 at 1:49
  • Yes. It's a crawl space with a sloped dirt floor (so the water comes through the dirt in little springs when it rains hard). Since it's a hillside, there's also a slab in the crawlspace that opens to the garage. The foundation is stepped in places, and I'm unsure how deep the footer of the foundation is.
    – Dong Shi
    Jan 10, 2023 at 1:57
  • 1
    This is far too broad and open ended. Unfortunately, a general "what do you think" question falls more toward discussion. Provide a solution and ask for problems, or list two possible solutions and ask pro/cons of them - that fits well with this web site's format.
    – FreeMan
    Feb 10, 2023 at 18:57

1 Answer 1


while waiting for you to dig the trenches which is the right thing to do and long therm solution, get a small sump pump (1/4 hp) with water leveler activation.

It can pump 3,000 Gallon per hour which might be enough to save your basement.

  • How would you go about digging the trenches? Is bringing in a backfill and digging a drainage trench all the way down to the bottom of the foundation the only way to do it, or do you think shallower trenches in a different configuration would work? I'm not able to find a lot of information on the internet about how to handle drainage in a Cut & Fill lot....
    – Dong Shi
    Jan 10, 2023 at 1:18
  • @DongShi any drainage you put in which helps surface water to flow away from your house instead of pooling and soaking into the earth behind the house (only to end up in your basement & garage) will help. Bringing in backfill to get the ground to slope towards the drainage will help too.
    – brhans
    Jan 11, 2023 at 1:09
  • What do you think the likelihood of the majority of the water coming coming from the other lots uphill is? The historical house documents seem to show a swale there to help with drainage in the past, but that did not seem to prevent the water intrusion (according to the house documents). Maybe a drain will be more effective?
    – Dong Shi
    Jan 11, 2023 at 3:06
  • @DongShi you will not get around digging and installing a drain pipe. You can use temporary solution as described in my answer. The uphill lots drain it down towards you.
    – Traveler
    Jan 11, 2023 at 4:26
  • Being near the top of a hill doesn't necessarily protect you from water draining in your direction. Friends of mine has nothing but a farm field above them --and not above them by much --but still suffered a flooded basement one rainy year when the water table under that field rose high enough to spill in their direction. So, yes, unless you have reason to be sure it's otherwise, assume it's flowing from uphill, not necessarily on the surface.
    – keshlam
    Jan 11, 2023 at 23:18

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