I have a question. We've all seen and heard the stories about wooden
houses being lifted off their foundations byu flood waters.
What I'm wondering is this. Are houses/other buildings of concrete
construction (block, o\\poured, whatever) part of the foundation? IOW, are
the outer walls "fused" so to speak to the concrete foundation, and as
such, how water-tight are they, or how water-tight *could* they be...?
What I'm wonderin is whether it's possible to pour walls and foundation to
be one unit, or even, if the foundation could be poured such tat it would
come partway up and the framing would go inside of it, and then the
exterior sheathing etc. would go on top or perhaps even over it...?
Just how water-tight could a place be made?
Links would be great, as well as any info or thoughts on htis. I'm just
trying to think whetehr there are better ways of coping with flooding, than
having stick-houses that jsut sort of sit on top of a concrete pad. IT
seems like ther ehas got to be a better way, so I'm jsut wondering.
Thanks In Advance!
In some places, even full concrete buildings won't save them, such as New
Orleans. I found this image interesting:
Normally, anchors are embedded into the concrete slab when it is poured, and
these anchors are used to attach stick built walls. In a pure concrete
building, it is basically like one monolithic structure, if we are referring
to cast in place, or similarly concrete block. The slab and/or footings are
poured first, and let dry, with rebar coming out where the concrete walls
will be. With concrete blocks, the blocks are formed as a wall with the
rebar coming through the middle, and then the middle cavities are filled to
form more or less a monolithic structure. Large buildings such as my old
architecture building, are poured in layers, beginning with the foundation,
all the usual rebar goes through the structure, but the forms are attached
directly to the concrete for the next layer and then the attachments are cut
off (in the case of our building you could see a pattern of metal rebar
looking pieces on the exterior walls where the forms were attached). Each
layer is poured onto the next, and these basically fuse to the one below it
to make one giant monolithic structure. But as far as I know, concrete is
porous and not very water tight. I don't know too much about water and
concrete personally so I'll leave that to others.
Well, that is a more extreme situation than I'm thinking of. I'm
wondering whether somethign could be at all water-resistant, and to what
extent. TO whit, if, say, 4 inches of water built up on a property, is
there a structure that could resist that. Well, aside from building high
;) I'm not talking about serious flood plains, such as South-East
Well, it sound like a *sturdy* structure would result, which isn't a bad
thing. Porosity - hmmm. I have to think about that - although it makes
me wonder why dams don;t leak like seives...?
I've just been looking at all the flood reports this week (well, all
Summer, actually) and this question popped into my mind.
3,000# Concrete is not watertight. 4,000# is much more watertight, but all
joints must be designed to include waterstops (6" wide ribbed vinyl or
rubber sheets) that must be lapped and heatsealed at the laps. An
interesting concrete system is Royal Building Systems from Canada, with pvc
forms that remain in place and form an impervious surface on both sides.
system is set up by sliding the plastic units together and installing rebar
as you go. I have a large carwash, detailing, and lube building going up
If your building is not heavy enough to stay put during flooding, a thicker
slab will hold it down. I've seen up to 11' thick slabs, and commonly are 3'
in areas with high water tables. Underground fuel tanks usually have to have
a slab to hold them down.
Better yet is to use an integral waterproofer put in the mix. However,
any openings (windows and doors) will render the waterproof concrete moot.
It is simply not possible to build a waterproof house unless you design it
as a boat that will float when the water gets too high. This is the only
idea I've seen recently that has any merit.
Bob Morrison, PE, SE
R L Morrison Engineering Co
I've always wondered about a house on pylons that are attached in such a way
as to be able to ride up and down on them. Then you just design the house
like a boat that will rise and fall with the flood. Would the pylons that
are pushed down deep enough survive a flood? Since the house is not
actually being supported on the pylons directly, what would the foundation
be? Then you have all the plumbing and electrical stuff to deal with.
Maybe if they are designed with break away points at certain places near the
ground so when it lifts, everything breaks off cleanly at a place that is
expected and could be repaired. I thought it would be an interesting study.
Isn't there a small neighborhood in the Netherlands that is doing that,
building houses that will float in a flood? I saw something on one of
those TV specials that mentioned this. I thought it was an interesting
Damn near impossible to make a building watertight as long as it has
windows and doors.
FEMA has published a couple of pamphlets on "waterproof" design, but they
are a joke. (as you might expect from FEMA).
You can make a building "Flood-resistant", but it would not be a house I
would care to live in. The only real answer is build above the flood
Bob Morrison, PE, SE
R L Morrison Engineering Co
Heh, spent a little bit of time recently at a flood plain conference.
Some of the T shirtswere amusing:
"Drove my Chevy to the Levee and the Levee was Gone"
I can't remember how it was worded but there was one saying, essentially
that you wouldn't build yur house on the median strip of a highway so
why build on a flood plain?
Is that in part because you need to make room for expansion and
contraction? ((This prob sounds like a stupid Q., but I don't know and
i'm trying to think of some way to discourage water incursion. OK, the
obvious way would be to not build in floodplains, and also, to build
houses on "mounds" just in case of a "freak flood".))
At any rate, thanks for the following description -= it's very
interesting - is this similar to how earthquake-resistant places aer
built? I recall having seen, at a Home Show back in California, a seciot
of "cinder-block" wall showing them all tied together using rebar.
Oh! That's tuight! Well, sorry for my "duuuuuh" moment there ;)
Hmmm, that *is* a point...
Well, that's intereting. Waterproof to a height of 8' - I'm guessing
that you had to have stairs going up to the door(s), and then dopwn into
the lower level...? Or was there a way to make the door(s) sealable...?
I'd be very interested in seeing a photo, if you have a link.
Thanks for the info -
So doors/windows can actually be waterproofed...? THat's interesting.
Not that I'm planning to live in a floodplain, but given the seemingly-
endless flooding that's occurred this year in so many areas, it seems to
me that the whole waterproofing concept should be getting more attention.
Or is it just too prohibitively expensive? OTOH I suppose even taht is a
moot question, since it's prob a lot like the question of quality - i.e.,
smaller but better quality versus humongous but cheesy. ((I know multi-
millionares can afford humongous and quality, but I'm thinking of more
I looked at the pic, not much visible. I googled it but no additional
pics. I was just curious ;)
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