Water Issue In Crawl & Foundation Settlement 4

[zero1238]

I completed an inspection yesterday for a client who owns a split level residential dwelling in New Jersey. The house itself sits pretty high on the lot with great, positively pitched grading conditions; additionally, all of the downspouts are extended and none of the air vents are at grade level. While these grading and drainage conditions are ideal, the property does have a small brook that runs behind the house, about 70'-80' off of the back foundation wall. The issue is, they have been having a lot of water infiltration into their crawlspace lately and there was even a small amount of standing water when I was there. Also, the front left corner of the house has experienced about 2-1/2" of settlement, which fluctuates across the front of the house. I have no problem handling the settlement issue, which will likely come down to some sort of underpinning piles, but I'm conflicted on how to handle the water, which obviously has to be dealt with. I imagine it has to be some sort of seasonal high condition with the ground water table but besides having a boring done, I guess the only way to check for that would be to check for mottling. They're looking to put an interior French Drain system in but I'm not sure if that will cure the water issue, which is what I'm trying to get to the bottom of. Any thoughts are much appreciated...

 

[milkshakelake]

I'd think that this is more of a geotechnical issue than structural. How does water seep and get into a crawl space through soil? I know about load paths, but I don't know the first thing about that.

I don't know if this is helpful, but when we have water infiltrating through the ground in mid-rise buildings, we use a vapor barrier and waterproofing under a structural slab. It creates uplift, which can be held down by piles or dead weight of foundation walls. It's somewhat expensive to do. I'd imagine that a drainage system is a lot more appropriate for a house.

Another silly idea is to use a slurry wall to create a sort of dam between the building and the brook.

 

[jerseyshore]

Not sure what town this is, but the water table is crazy high just about everywhere in NJ. I've owned my house for 2 years and the sump pits in my basement never even had a drop of moisture until last weekend. I'm on all sand so it's not really rain water getting in, the water table is just so high all over the state.

When you say they have had water issues lately, are they talking about just in these last 2 weeks with the crazy rain every 3 days or has this issue been going on for a year or more?

There's only so much you can do when the water table rises this much.

 

[jerseyshore]

Generally, around here, it's important to get a good local waterproofer. 90% of the companies are scams. Filling the crawlspace with crushed stone or gravel and using a vapor barrier is most common.

Have to be careful with sump pumps, since clearly they have a soil issue with the settlement already found. I can't tell you how many sump pumps I've seen undermine foundations because they are installed too low or run too consistently and pump away clay or silt along with the water.

There are a fair amount of underground streams in NJ that could be causing both of these issues. A local geotech might be a good place to start.

 

[EdStainless]

Sounds like an intercept drain behind the house and routing it to the sides where it can then drain downhill.
Using pumps to force dewatering is a risky business.
Trust JerseyShore on this.

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P.E. Metallurgy, consulting work welcomed

 

[jerseyshore]

I know it's not always feasible and these waterproofing companies are in the money making business, but I really wish they pushed more exterior drains Ed. I want water addressed on the outside of the foundation not when it's already in the house. But they convince people to spend $70k on "waterproofing" their crawlspace when the solution is a simple exterior drains buried in gravel.

 

[zero1238]

I should say that this job is in Freehold, NJ. I may have them contact a geotech engineer to further clarify conditions. I believe there has been an ongoing water problem but these last few weeks have certainly exacerbated it.

@jerseyshore - That's a good point about the sump pumps, I've seen that happen before. Where around the Jersey Shore are you located? I'm from the Jersey Shore as well.

 

[JAE]

Don't neglect to consider possibly a leaking water pipe serving the house.
Sometimes long term settlements and/or freezing can crack a pipe or a fitting underground and dump a slow, steady stream of water into the lower areas of the house.

If the local water company uses fluoride in the water you can have some of that water tested for fluoride to see if it is the source.

 

[jerseyshore]

I am in northern Ocean County. HBU?

Freehold isn't a town that I would say has a lot of "bad" soil so I would operate under the assumption that the two issues are related.

It's rare to find significant settlement of foundations in pretty good soil towns unless it's a super old house with a brick foundation, rain water issue, leaking water or sprinkler pipe, bad sump pump/ waterproofing, underground spring or stream, aka an "outside force".

 

[zero1238]

That's interesting, I'm from the same area.

And that's true, although I have run into expansive soils in Freehold before. I also was thinking there might be a shallow lens of silt, given its proximity to the brook behind the house; who knows if that was a larger body of water at some point. I'm probably going to have them complete a soil boring with continuous sampling down to 12' to 15' to find out.

 

[JAE]

After 10 years in south Texas (with expansive clays galore) sometimes what you think is a downward settlement is really an upward heave in other areas.

 

[jerseyshore]

Also, as a rough rule of thumb, in most of NJ, houses were built with basements. Bi-levels, split-levels, and houses on crawlspaces were typically built like that for a reason. Usually, water, like in our area of Ocean & Monmouth counties. Obviously if a house was built into a hill or had some unique grading that could be the reason for these shallower foundations too.

But unless an entire neighborhood is all split level houses (same builder), there may have been water issues at this house and that's why they didn't dig for a full basement. Majority of the houses along the coast that have Yankee basements were done like that because they dug down until they hit water, then went 4"-12" above that. Similar thing was done with crawlspaces. Now, as the water table has risen and bad storms seem to happen every other week, lot of people are getting water in places they rarely did before.

 

[zero1238]

I can see that being the case. I think with this particular situation, I don't see many other water remediation options other than implementing a french drain system. There is somewhat a limited amount of tricks for this type of scenario but I could see that helping. Especially if we do find some sort of lens of silt, given its proximity to that brook in the rear of the property.