Crawl Space + Regular Flooding = (my (very) Long Post)

fixitpete

a) I can try and get you a couple pics asap.
b) no erosion trouble at all. The subject has been there since 1920 -- no settling issues. All footings are in good shape.

What are you thinking about?

Cole

Thats great to hear, I like to think about everything and start from ground zero, if all footings are in good shape, now we can work on a solution with knowing that we wont be into bigger problems down the road. I would like to take a look at the photos to get my brain spinning some more.

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fixitpete

Excellent!

Ok. I should have pics... hopefully this weekend. I was just doing some brainstorming with my partner on this job (yeah on xmas eve!) -- and we came up with a really interesting thought.

Step one:

Grade soil to a low spot... say one of the corners, or a valley in the center... whatever.

Step two:

We can get 20mil (yeah, 20 mil!) vinyl sheeting (uv resist, flame resist, etc. (they are actually used billboard covers) This stuff is SUPER tough... we put that down, (go up the foundation walls, say a couple inches shy of the sill plate).

Step three:

We cover the sheeting with gravel (not sure of size (yet). (purpose of gravel to keep sheeting down during flooding)

Step four:

@ the low spot of the grade we set a float activated submersible pump. so when there is flooding the pump runs. Now granted -- the pump will NOT keep up with the tidal flow (since the entire city is under water!) -- but once the water recedes, the surface of the sheeting, under the gravel should be somewhat dry.

Anything to this, anything I can omit? Thoughts?

Until you have a picture... you're really looking at an average coastal very wet crawl space with 30-36" of room between dirt and bottom of subfloor.

neolitic

Some exterior pix for context
would be nice as well.

Anything like what I'm getting
from your description would
be on stilts in my experience.

The whole city is flooded at high tide??

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A W Smith

On that sump pit I was thinking to isolate it from the water table somehow. Maybe by burying a precast sump pit. and pitch grading to it. As far as the water table lifting the rat slab, how much lower than the surrounding grade is it?

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fixitpete

I would say that the top of the soil line is around 6"-8" below surrounding grade. I like where you're going with the buried sump pit. I'm thinking pastic. loaded with gravel to keep it down. Below grade, but with the only opening coming in from the sheeting... so the water table can't get to it, and it will only run when water is being directed to it from above.

Hmmm... I likey.

I likely even more if I can do it with a tarp>gravel>rat slab...

(Neo, nope. No stilts. Actually, if I was about another 8" above my current finished floor height, I wouldn't even need flood insurance. --- the problem is that during a storm AND high tide you can get some fast flooding -- it rolls in and out quickkly, but we can't have that water under the house sitting on a tarp when it does recede.)

Cole

Thats what I was thinking, your plan sounds pretty good. Give us some photos, when you can and I am sure you will get some more information.

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A W Smith

ah yes a sewage ejection pit would be perfect. you can even bolt the poly sheeting between the lid and the pit gasket. Its large enough so that you can put several concrete blocks in it without obstructing the pump. and the lid has knockouts to drain into. Only thing is you will probably have to dig 30 inches which puts you well below your existing water table.


oh heres a short one botton of this page

http://www.septicsolutions.net/store...sinSystems.htm

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fixitpete

Ya know... I think we may be on to something. You're thinking, and correct me if I'm wrong -- is to use a pump and enclosure (like the one on the bottom of that page, or 3985C, the one above it) EXCEPT modify the basin so that water can only come in from the TOP... are there holes on the bottom or elsewhere that I'll need to deal with? (no big deal if so)...

Burby

What would prevent the concrete slab from floating out of the ground if your water table is that high and rises 10 plus inshes above ground several times per year?
Or is the 10 plus inches run off or overflow? But I would still think it would affect the water table & again, cause the slab to rise and cause more possible damage with the movement.

Have you spoke with your local building dept to see what they may recommend for this problem or a civil Engineer even?
Any money spent without a sure proven result will be a possible waste.

Some homes just have to be as is unless raised as most homes have to be per codes today.
What have others done, if anything, in your area to help with the water problems?

Your floor joist & sub floor must be covered with mold spores, I would think, not to mention between sub floor & finish floors. Have you had any problems that you know of?

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A W Smith

I doubt that a water table will cause the slab to float, you dont see too many houses that are on slabs float away when that happens,


fixitpete

those sumps on that page are already sealed, they have knockouts on the side, they are sewage ejection pits which by design are sealed all around even with the lid.

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fixitpete

Burby: People in my area:

1) do nothing and have the dirt, like this house has been for 80+ years.
2) Rat slab
3) plastic tarp

No rot or damage (some termite, but that has been mitigated about 10 years ago and all houses in area are going to have termite/borer issues, if not treated). There is some ground mold (which is a major reason I want to do this right) (a white-ish surface mold)... As far as the slab "floating away" -- There are many other with a rat-slab, and actually the front half of the house and the back half of the house are both rat-slabed and have no problem... so it is a possible solution. However, if I can do it with 20mil vinyl (UV/MOLD/Fire) and be able to access my utilities easier if needed (city sewer/water), AND safe money... well... that's good too!

Al:

I think I'll call Little Giant (or similar) and pick their brains for the application... I think a huge part of this will be in the prep work (grading)...

Thanks for the ideas and brainstorming! I appreiciate it!

ry-con

My own house has similar situation
1 Install drainage tile inside the perimeter of foundation and sump pit with drainage aggregate
2 Fill foundation with sand as much as possible.(raising the flood plain)
3 Set the pump float as high as possible-just below grade-interior
4 Install 6 mil plastic over grade.
5 install aqau gaurd or tar-paper under hard wood floor.
The pump will not run 24/7 because there is always a perculation time
Concrete&plastic is great but if you don't releave the water below it will heave the concrete.
Remove all that crap in the floor joists
If the house is dated then check joists & sub floor for decay!
There are better solutions but they come at a $$$$.

fixitpete

I hope to have some pictures of this later today or in the morning...

Here is where we're at with this so far:

I really appreciate your input on this. I've consulted with several concrete and moisture abatement people that I've dealt with over the years and it seems that as long as we conform (somewhat) to ASTM 1993 and add a surface pump we will significantly reduce the moisture in the crawl space, allowing for installation of the material that we're after.

Basically, the plan is as follows:

Grade soil toward the lowest point, in this example, toward one corner. The thinnest section of slab shall be 3" --

Next a vapor barrier that conforms to ASTM1993 (WR Meadows or Bituthene (I *THINK* "System 4000" conforms)(?)

at the low point we're going to J-Bolt a starboard (heavy plastic) material that will receive a surface mounted submersible pump. This pump will only run when water accumulates from flowing off slab, or during a flood (during a flood, it won't stop until water recedes or water is vacated.)

Pour slab.

Done.

This -- In combination with Aquabar-B (just because) -- should provide an exceptionally good substrate and environment for our materials.