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Old 02-16-2011, 11:08 AM   #1
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Subfloor in a Flood Zone

I currently have a project to build a subfloor for our future bedroom in our old garage. However, the issue is that my property gets flooded now and then, due to living near a creek. We would occasionally get maybe 1 inch of water in the back room where our room is to be about once a year...maybe every couple years.

After reviewing how to build a subfloor, I purchased 2"x4" x 14' lumber, along with 3/4" plywood and of course, insulation.

Now, its time to start building, and I read to lay down 6mm plastic sheeting on the concrete floor, then build the subfloor directly ontop of that plastic, where the plastic would act as a moisture barrier. I plan on applying the plastic to rise about 6"-12" up, on the wall studs, to keep the occasional 1" water out of that room completely.

However, when I talk to my dad about this, he is adimate about building the floor up a few inches, and creating a 12"x12" area on the floor for a vent for airflow. However, I dont understand the point of laying plastic on the concrete.....then building the floor a few inches above the plastic, and having a the plastic is acting as a moisture barrier, therefor, the space between the plastic and subfloor should not have moisture there at all.

Is my method (lay plastic on concrete, build subfloor directly on plastic) the correct way to go about my build? Or is there another way that I should build this subfloor in a room that gets the occasional 1" water.


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Old 02-16-2011, 11:22 AM   #2
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Hey Lukew,
Air flow is important underneath the subfloor. Have you looked into a product called "DRI-CORE"? Using dricore would solve most of your problems.

When your basement floods the water usually isn't seeping in from the floor. The vapor barrier would protect against small amounts of moisture to prevent mold and other damage. If you used dricore you wouldn’t need a vapor barrier.
Do you have a subpump? I assume that you do because of the area that you are in. The water collected around the foundation is drained into your subpump pit in the basement. Then the subpump pumps the water away from the house. Usually if you are flooding it is because the pit is over flowing. If that is the case then you should invest in a larger pump and backup system. Good luck, I hope this helps-Gregg


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Old 02-16-2011, 11:37 AM   #3
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I uploaded a picture to give an idea of what im trying to deal with. Unfortunatly, we do NOT have a basement....probably because of the flooding issue. Then again, not very many people in my town have basements.

Water doesnt come in the house often enough to buy a when we do get water....its such a small amount, I doubt the pump would be able to suck it up at all.

The concrete is at ground again, it was originally a garage.
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Old 02-16-2011, 12:16 PM   #4
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Originally Posted by gotogregg View Post
Have you looked into a product called "DRI-CORE"? Using dricore would solve most of your problems.
this stuff is neat, but I thought it was expensive... it was close to $10/2x2 panel, plus the shims..

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Old 02-16-2011, 02:37 PM   #5
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Dri-core was the best decision we made regarding our basement remodel. Theres an important distinction, however, between the functionality of a moisture barrier which is intended to defend against natural moisture buildup from air flow, temperature changes, and porous and non-porous materials...and essentially preventing flooding. As my contractor explained to me - the Dri-Core will definitely help the occasional instance of water seepage through cement blocks onto a concrete floor, but it will do little to alleviate damage from a flood of several inches of water. But another great benefit of the dri-core is the added insulating that it provides. Having the floor elevated off of the cold concrete floor vastly improves average temperature in the room, and eliminates the 'damp' feeling that most basements have.

One other suggestion would be to install french drains around the perimeter of the garage structure. While I know its not a basement, you could still in theory provide a means for any water entering the space to be collected and pumped out via an ejector pump by simply digging a small well and running perforated PVC to it. Not sure how much of a 'flood' situation you are talking about, but if it more from seeping groundwater or rising water table (versus massive runoff) then a sump/french drain combo would help keep you dry.

I had a VERY wet basement. Flooded on 3 sides with any heavy rain. Had the french drains installed on all 4 sides, with a deep sump pump well and PVC. The walls were waterproofed before the vapor barrier was placed behind the framing. As an additional deterent to moisture and critters, the contractor also put the vapor barrier under and above the sill plates (top and bottom of framed wall studs) and siliconed the junction before putting up mold-resistant drywall.

Hope this helps
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Old 02-16-2011, 05:23 PM   #6
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You might want to check with the local building department to see if you are in a flood zone, and if so what the hundred year flood elevation is. If the water rises a few inches above floor level every year or so, it is likely that eventually you are going to get a really large flood that will flood your basement six inches or more, which can destroy your investment in subfloor, flooring, and maybe the contents of the bedroom. If this is the case,you may want to consider raising the floor level to above the anticipated high water line, or at least purchase flood insurance so you won't be wiped out if the worst happens.
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Old 02-17-2011, 02:49 AM   #7
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We had our "100 year flood" in 2007, and there was approx 3ft of water inside the main housing structure. Dri-core isn't an option for me, as I already bought the materials....and it wont help leveling out the floor (it slightly slanted towards the middle where an oil drain was). Any sort of water pumping device would be worthless, as you can see from the photo posted below. We're techincally not in a flood zone, therefor they will not sell me flood insurance (already had a big ordeal with that with the 2007 flood with my neighbors). The photo posted below is a very RARE flood....however, in this particular when we received about 1in of water in the garage. With all this in mind....again, I just wanted to know....if in normal cases, would the concrete --> Plastic --> Subfloor stop mold groth in normal conditions (without flooding).
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Old 02-17-2011, 12:52 PM   #8
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OMG, why do some of you guys answer without reading the HO's question and description of his house?

The is NO basement! It's a garage.

Luke, You are planning some thing that is highly NOT recommended. You live in the wrong spot to do what you're proposing.

TILE GUY - retired- TROY, MI - Method & Product suitability consulting.

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Old 02-18-2011, 07:43 AM   #9
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Subfloor in a Flood Zone

You may want to take a look at Tyroc. You can view more informaiton about it at This is a subfloor product that was made as a solution for wet basements and slab on grade. It is not made of wood. Does not absorb water and will take any finished flooring product you choose to use. It acts as a moisture, vapor, anit-fracture and decoupling barrier all in one. Tyroc will not feed mold or mildew. Tyroc also acts as an insulator and in normal conditions raises the temperature of the finished floor by about 15 degrees.

However I would agree to some degree with JazMan and jkr77 in that no matter what you do here if your floor floods you will have issues. Yet the tyroc can be dried off after extensive flooding without destroying the tyroc itself and it will not change shape (i.e. expand or warp).



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