Crawl Space Encapsulating in Flood Zone


Old 01-02-19, 09:25 AM
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Join Date: Aug 2012
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Crawl Space Encapsulating in Flood Zone

Hi All,
We have an old farmhouse we use seasonally in Northern PA in a flood zone, and it floods into the crawlspace when the nearby creek floods significantly. Crawlspace floor is right around outdoor grade level. Over the numerous floods in 130 years or so there's been significant degradation of the building structure in the crawlspace, so we called in a waterproofing company to quote some repairs. In addition to sistering/replacing the rotting structural members, we'd like to do something to remove any flood waters that get in. (Note: it is generally dry in the crawlspace when it hasn't flooded, although can take a long time to dry out). Waterproofing company recommended encapsulation, sump pump, and dehumidifier. This generally sounds good to me but just wondering if anyone has specific experiences with crawlspaces in flood zones and if there are any special considerations to make. This company doesn't seem very concerned about it, and isn't offering much in the way of advice or specific suggestions for the flooding issue. Any firsthand experience or specific knowledge of engineering the most effective system for my situation is greatly appreciated!
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Old 01-02-19, 09:41 AM
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Well, my experience is that old German farmhouses by creeks in PA were often be built over a spring to have flowing water, they were designed to have water running THROUGH the basement and down to the creek.
English, Welsh and Scotts-Irish settlers would usually construct a separate springhouse on the farmstead, while German farmsteads seemed to incorporate the spring house INTO the basement of the farmhouse if they could.

This makes sense if you think of English winters (mild winders with little snow accumulation thanks to the Gulf Stream warming the British Isles) in comparison to German winters (heavy accumulation of snow in the center of the continent).
Old 01-02-19, 10:22 AM
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When it floods, how much does it flood? Inches of water?

I haven't done much research on encapsulation when it comes to flooding, but I'm not sure how well the encapsulation system would hold up to significant water under the plastic. If the sump can keep up and keep it just wet and not flooded, I think you'll be fine, but if you have inches of water under the plastic, I can imagine it floating up, the caulk/glue seals breaking, etc. and ruining the system.

Do you think the size of sump they are planning will keep the water out of the space? If the stream level actually rises to that level, any size sump pump isn't going to help.
Old 01-02-19, 01:32 PM
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Don't know for sure since we've never actually been there while it's flooding. We do know that water gets to the front porch (maybe two inches below the front door threshold), but never floods the first floor. The porch is right about at the height of the top of the foundation walls. Not sure if water gets in to the crawl space through the foundation walls and/or access holes, or if its coming over the top of the foundation. Either way I'd bet there are inches or even feet of water in there. Again, hard to know not having seen it during a flood. There may be some standing water by the time we show up a week or more later, but its never covering the whole floor at that point as the soil is very sandy and drains well. They were quoting a 1/2 hp Zoeller pump that did something like 4000 gallons/hour at zero head. By my estimate that could empty a completely flooded crawlspace in less than 5 hours. Of course, not knowing the rate at which it enters the crawlspace, hard to know if it could keep it dry versus just emptying out floodwaters once they receed outside. It seems a little far fetched to design a system that keeps the space dry during a flood, so we're primarily looking for a solution that keeps it dry down there normally, and allows for the fastest possible removal of flood waters and drying out after a flood.

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