advice on flood damage prevention

Hi,
I have some crawlspace vents near the base of the house that are 16x9. I am getting sandbags and plastic ready in case, but I read that cutting plywood boards to place up against the brick, and then seal, is a good thing as well. I know I could get some weatherstriping and stick it around the edge of the plywood, then place plastic, then sandbags.
However, after looking at doordam.com, and reading that they recommend putting a bead of DAP around the edge of their product to protect against seepage, I was wondering about doing the same thing around the crawlspace areas.
Is there a sealant that I could place on the plywood in an extra thick bead, and then just press it up against the vent, secure it with a sandbag, that would allow for easy removal later? I'm assuming that the DAP would have to be applied way ahead of time for it to dry, but I might be in a position where I would not have a 12 hr dry time.
I know that there is a sealant for roofs that will provide a 'wet seal' in the rain, but it is like tar and might stain the brick. Or would this be ok?
Also, there is one crawlspace vent near the HVAC that has a power box above it and a thick cable comes from the box and goes through the vent, making the placement of a board difficult. Could I just seal up this vent without any problem? This would leave 6 other open vents, and two of them are fairly near this one with the cable. What would be a good material to seal it up with that I could do myself? It is on the back of the house so cosmetics are not that important.
thanks,
itchy
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wrote:

seepage you can try to seal out, if its flood water you cant expect the structure around the crawlspace to withstand the water pressure, it can collapse the building. thats why you often see a flooding home with doors open letting the water in, to prevent structural damage.
so good luck with the sand bags, dont even try to seal water out, it could move your home off its foundation
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wrote:

I would not get too concerned with forming a perfect, watertight seal around the crawlspace vents. It's likely a fair amount of water is going to find it's way through various cracks, holes, etc around the whole perimeter. Your objective is to greatly reduce the amount of water that can flow in, not eliminate it. To seal between the brick and plywood I would use some auto body putty, which should be available at local auto parts stores. It's kind of like plumber's putty. Grey, pliable, never hardens and you can form it in your hands into long round pieces. Easy to remove later.
Also, I don't know how high the crawlspace wall is or what condition it is in. But at some point, another factor comes into play. And that is that if you have 3 ft of water pushing against an old brick wall with nothing on the other side, it becomes a lot of force and could cause the wall to collapse in. Meaning it might be better to let the water in and deal with that.
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[...]
[...]

I'm basically guarding against a 50 yr event, which would amount to maybe 6-8" of water. The crawlspace is small, you can barely squeeze under there to install ductwork, I know the HVAC guys were kidding me about it.
I wanted to seal out water because I heard it could rise through the floor into the house, but after thinking about it, that would be a lot more than 6-8" of water. Maybe the quickest way would be to put up plastic tarp, then a board, then a few sandbags, if seepage is unavoidable. I'm not in a flash flood area, so the creek rising would be fairly slow and likely would allow me enough time to place the bags. Thanks for the advice everybody.
itchy
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internaughtfull wrote:

Why do you want to keep water out of the crawl space?
If I had that issue, I'd crawl in the crawl space and dig a pit - not very large, but enough to act as a reservoir. Then I'd get a pump...
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On Sat, 12 Mar 2011 09:33:09 -0800 (PST), internaughtfull

If I were to do something like this, I'd just glue a piece of foam rubber on the whole piece of wood. It's not like there's a window in the middle that you have to see through. And you're not going to want to spend a lot of time positioning the wood when the flood is coming. For one thing, you won't start until it's near, and there will be many other things to do.
But....if the window isflooding on the outside of the house, the ground beneath it on the will soon be saturated on the outside of the foundation, and the crawlspace will be getting water right after that.
Maybe before that, depending on when the saturation occurs.
Am I not right?
I have a stream behind my house that can rise 10 feet in 16 hours, and has risen to one inch from and one inch below my property line. So I've thought about stuff like this. Every time I see floodign on the news. FTR don't have a crawlspace, just a basement.
I've even thought about renting an excavator at the last minute, to open up the channel downstream from my house, to prevent the flood from reachign my house, but there are several reasons not to do that. It's all private property, the bottle-neck, the channel is all rock, I've never driven an excavator, I can't tow it, they probably can't deliver it in time; they'd have to deliver it to someone else's propert (the swim club down stream from me, that I don't belong to and woudlnt' join.), if it gets that high it floods their parking lot which is wide, so maybe there's not much point to widening the channel.
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That's not a bad idea, maybe that stick on weather stripping that people use on miami windows, its 1/4 to 1/2 " foam. That plus the bags, plastic, sounds fairly good.
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>

Yes I thought it amusing that the city said 'this is on you' to figure out but if I dug anything around the bank, then I had to get a permit to do so. They did help though in creating a better ditch line toward the vent pipe that empties into the creek however, taxes at work. You could always look at a decorative/functional retaining wall to simply divert the water away from your property at flood time. A good mason could do it. Probably expensive though.
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On Thu, 17 Mar 2011 07:38:16 -0700 (PDT), internaughtfull

Don't attribute that to me. That's what I was saying NOT to use. There is no reason to make it that narrow, providing less area to hold back the water and less area to to glue the foam to the wood with. And you can probably buy sheets of foam almost as cheaply, if you provide your own glue and don't expect it rolled up and in a box. If it is foamy on one side but sheet-like on the other, you can glue to the sheet-like side, although I've also glued to the foamy side, the side with open holes.

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