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

fixitpete

WHY I VISITED

Hi folks -- I found my way here from the flooring forum and am a framer by trade -- who somehow and someway has found himself doing a wood floor installation (ask my wife how it happened. ) over a crawlspace that is sort of a unique application. I have been reading: "Insight: New Light in Crawlspaces" and have many questions about a unique application

HISTORY

The subject property is in an extreme coastal (salt water) location, approximately 25 feet from bulkheaded tidal water. Usually, if you dig 12" you will hit water, at higher than normal high tide the water level will be ABOVE ground level. This means that the crawl space will have anywhere from 1" to 10" (or more) of water probably 30 days a year, and ALWAYS will be damp. House built in the 1920's.

CURRENT SITUATION

The crawl space is dirt-floor (more like mucky sand) and is approximately 30-36" from the underside of the sub-floor. There is no ground cover vapor barrier of any kind. The joists are insulated with a combination of insulating board (the old kind, not the poly-iso), and/or fiberglass. And yes, the insulation is "wet" just like the "Insight" article says will happen! (GREAT article, by-the-way)! There is NO insualtion on the foundation walls. There are vents, assumingly because we are in a flood zone and for ventilation.

THOUGHTS AND PROBLEMS

I would like to put down a vapor barrier on the gound but have the following concerns:

a) If I use 6+Mil Plastic, what keeps it from moving around when the flood waters come? Plastic isn't going to keep 10" of water "down"

b) If I *do* use the Plastic and the flood waters come, then the water will "pool" on TOP of the plastic, I can't think having a "pool" on top of the plastic just standing there is a good idea, how do you deal with that? Grading the soil MAY help, but the soil WILL move with the flooding, creating "pockets" where the water WILL stand. So my thoughts are: is there an approved "membrane" that will keep vapor from coming UP but allow water to go down? Kind of like the weed-barrier used in landscaping?

Next thought:

I would REALLY like to have a crew come in and do a rat-slab down there -- it would make for a REALLY nice environment for other trades to work when needed and I think be cleaner and drier (?)... I know others in my area have the a rat-slab, however I don't know how it will help my situation -- just somthing to think about. What should I look for? Due to the high water table, should there be or NOT BE a plastic barrier of some kind in addition to the slab? Or will the pressure from the ground water push the slab up of there is plastic under the slab?

----

That takes care of gound cover... now let's move to the insualtion @ the joists. I have read over and over and over on this forum and in the "Insight" reading that having insulation in the joists is nothing but BAD. However, given the flood issue, what are my options? Insulation the foundation walls (even with poly-iso) or some other closed-cell insul, probably won't last long...

Any input would be much appreciated.

Thanks, Pete

neolitic

I think I'd start with drainage tile,
pea gravel, a sump pit, and a pump.
Then a vapor barrier on the ground.

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fixitpete

A sump pit and a pump? Care to explain how that would work exactly, you know seeing how if you dig about 8"-12" you hit an infinite supply of water?

I know framing is the top half of things... but I would like to think a little more help is around these parts.

fixitpete

For example... if you were to do something like this:



And then a flood comes...

Where does the water that is on top of all those little "valleys" of plastic go?

neolitic

Every major building in downtown
Indy ( and a lot of other major cities)
has de-watering pumps running 24/7/365.
I.E. an infinite supply of ground water.
If you have a house at sea level, 25 feet
from the ocean you've got some problems
to overcome.
All I can see is a big pump, or a moving van.
Perhaps someone in your area (where ever
that might be ) could tell you
how to go about installing a vapor barrier
under the floor joist.
That is not a common thing in my part of
the world, out side of boat houses.

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fixitpete

1) Atlantic County New Jersey. (I got the hint in your sig.)

2) There is not a single home or other structure in my zipcode that has a sump that runs 24/7/365. Or at least none of the hundreds that I have crawled around in.

3) People in my area either:

a) put in a rat-slab
b) put down a vapor barrier (6+mil poly) on ground, and deal with the puddling, that eventural evaporate in about a year.

My point is that I don't really care what people do, I want to do it right. I've been around long enough to know that what most people do isn't right.



Are there "breathable" barriers, where the water can go down, but the moisture can't come up?

neolitic

A sump pump in your case would be
just to keep up with the water, not
eliminate it.
You can either pump the water to keep
it below a vapor barrier on the crawl floor,
or raise the vapor barrier to the bottom
of the floor joist and let the water
have its way below.

Do some research here........
http://www.buildingscience.com/index_html

I don't remember anything directly
on point for your situation, but maybe
something will ring a bell.

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fixitpete

Thanks... I've been scouring that site for info. Most of it assumes a pretty dry area already... so there isn't much there. This is such a harsh environmental subject property that it makes it tough. I *am* thinking about applying the vapor barrier to the underside of the joists instead of the ground.

I don't know the ramifications of that on "trapping" the humidity between the plastic and the bottom of the subfloor (and insulation that is there)...

I'm going to pick a few brains over the holiday and see what I net.

neolitic

Bump

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neolitic

C'mon, no opinions in this group?

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fixitpete

I appreciate the bumps. I know it is a tough application.

Thank you very much.

Wdavis3910

You can remove insulation and paint or stain all floor joists, sills, girders with Copper brown stain or exterior paint. Copper brown stain can be purchased at Lowes - use a full face mask. Protect Eye's. There are some stains that are less toxic on the market.

If you install a moisture barrier on ground poke small holes in plastic with a screw driver, this will allow water to drain under plastic when water level drops.


Tom
William Davis Builders

fixitpete

Wouldn't putting holes in the vapor barrier negate the purpose of the barrier?

neolitic

Yes.

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fixitpete

Thought so.

Brainstorm.

Since the key reason for this work is to stabilize the humidity level of the subfloor and prevent damage to a new hardwood install... I'm wondering this:

What if I can:

a) find a membrane to put on the crawl floor that will allow water to go DOWN, but not up (like the weed barrier I mentioned earlier -- but for water)
b) I am already using Aquabar-B as a moisture barrier on the subfloor (under the hardwood install)... what about something like RedGuard of the like?

neolitic

How about I put some lipstick
on a pig, will you marry her?

Your floor system wants to be dry.
It wants to be @ the same humidity
level top and bottom.

I'd put the hardwood on hold
til I solved the real problem.
But then I don't like to throw
good money away.

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fixitpete

Will do.

Thanks for the advice!

P.S. If anyone knows of any answers to any of the questions regarding materials, etc. (above) please let me know.

Thanks!

A W Smith

is there enough room in the crawl to regrade it to pitch to a sump depression with poly?? and pour a rat slab over all that poly to keep it down when the tide is up?

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Cole

A couple of questions before we get into more detail:

But I would love to see some pictures of your crawl-space to give us some more information on what solution might be best to fix it.

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fixitpete

To answer your question.

Yes, there is enough room - you could grade to a valley with a sump. However The sump would run 24/7/365 due to sea-level.

Also, yes. You could pour a rat slab, and this is something I've thought about... my one question is how does the hydro-pressure on the poly under the slab end up? I'm thinking you'd have heave-age and other issues... no?