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Crawlspace Water Advice Needed for new build

Lora P
2 years ago
last modified: 2 years ago

Hi Houzz! I have been really impressed with the cumulative advice out there and I was wondering if anyone could weigh in on what might be a unique crawlspace water problem we are having in our new build in a unique location.

Okay - so we are building a home in an old reservoir. It's overwhelming and crazy but everyone said it would be fine. It is an amazing site. Here is the backstory - A natural rock bowl on the side of a hill was dammed up 150 years ago and for a period of about 30 years, it supplied our city with water until the city outgrew it. It does not have a natural water source; water was pumped in from a river that is downhill of it - like 1/2 mile away. The dam now has a firetruck approved arch through it put in by the previous owners so water readily flows out through it and the open pipe that flows out under the dam (think tub drain that there is no plug for) - there is never accumulation of water in the dam. Because this lot was undeveloped for many years and was city owned, the houses around it that were built in the 1960's and 70's designed their lots to drain into ours. California has been in a drought for a few years so no one else really appreciated the amount of water that would flow through the lot until we have been having heavy rains the past couple of months.

So, fast forward to now. We developed the property, ran utilities to the center of the bowl, and have built our house there with a garage slab foundation and the rest of the house over a crawlspace. There was a natural flow of water that ran down the middle of the property and we designed the house to miss this flow and be on a higher part of the bowl, but when the foundation layout was staked, we realized the design engineering firm had made a mistake in their topo and the side of the house was in the middle of a giant rock outcropping, so we had to shift the house over 8 feet such that the corner now eclipses the place the water previously naturally flowed.

There is a design for drainage that the architect made that has not been fully executed. Swales aren't in place and it's not graded correctly yet. But, at this point, we aren't sure if the design is sufficient given the amount of water in the crawlspace (mostly under the vapor barrier, but some gets on top with the joints not appropriately sealed). The construction engineering firm designed additional drainage quoted at $30,000 including french drains around 50% of the house (there is a lot of rock and they plan to go 3 ft down). We aren't sure if A. This will work or B. Is necessary with the amount of rock around the house. I am thinking we might bring in a crawlspace company now to give us their thoughts and a quote and/or landscapers, but my spouse wants to wait and try to carry out the architect's plan plus a few surface drains and then bring in the crawl space experts and landscapers when we are done with the house (we are 2-3 months away from completion) and the site is not under a GC's control. My thought is that crawl space experts will have seen problems like this before and might be better at figuring out the right solution the first time.

Foundation is dug down to bedrock, quickrete, then stem walls. Crawl space is 3 to 6 feet tall.


So, any thoughts at this point with info provided? Should we bring in a crawl space expert now? Will they be able to advise on drainage? Advice re area drains versus French drains in a highly rocky area (that's why they put a reservoir here)? How bad is it to have some water flowing under the vapor barrier (there is a drain that it gets out of so it is mostly not sitting water)?



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