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Old 01-07-2012, 03:55 PM   #1
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New Basement - Best Way to Waterproof


I'm in the planning stages of building a new cabin, and am thinking of including a basement. I like the ability to have a cooler room in the summer, plus the added square footage, so the basement is very attractive. However, my major concern is waterproofing. Any suggestions on what the best methods are for waterproofing (french drains, lining, etc, or any combination thereof)? I don't think water table is an issue here I have a well that didn't hit water until ~30'). I'm more concerned with water runoff, rain, and snow (I'll have basement window wells also). I've attached a diagram of the layout - the cabin is up against a hillside with a 6' retaining wall. To further complicate things, this is an off-grid weekend-use cabin, powered by solar, batteries, and occasional generator use. I'd like to design it so I don't have to rely on a sump pump, given the high wattage requirement (it would be too much for my solar). Another bit of information - if I did some kind of french drains, I can run piping from them to ~100' from the cabin where it is sloped and they can gravity drain into open land.

I'm going to have a contractor do the work, but it's in a pretty remote area so my selection of contractors is limited. I'm trying to do as much homework on my own in advance to determine the best way to design it.

Thanks!
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Old 01-07-2012, 04:17 PM   #2
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New Basement - Best Way to Waterproof


I am no expert on this, but it looks quite risky for a basement, to me. If you could move the cabin 15 to 30' away from that cliff, you would likely be far better off. I see water pouring over that wall and raising hell, w/out any ground tapering away from the cabin to shed it. Also, water down at 30' seems shallow. If you dig down several feet, can you compact the soil into a ball? What type of soil do you have? That affects your decision, too.

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Old 01-07-2012, 04:25 PM   #3
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New Basement - Best Way to Waterproof


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Originally Posted by jklingel View Post
If you could move the cabin 15 to 30' away from that cliff, you would likely be far better off.
^^This. And put in a french drain or even a full on culvert in the gap.

hth
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Old 01-07-2012, 04:30 PM   #4
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New Basement - Best Way to Waterproof


Does that wall exist? I suggest a beefy drainage at the toe behind the wall. 3 or 4" perforated rigid pipe with 1' wide section of 3/4" crushed rock from the bottom of the wall to the top. Then trench and install a non perforated pipe from the lower end of the perforated pipe around your basement structure to carry all of the hill water away.
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Old 01-07-2012, 04:35 PM   #5
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New Basement - Best Way to Waterproof


I have to agree, that's about the worst place you could try and build anything.
Simple water runs down hill, all that water coming down the hill will tend to just pile up again the foundation untill it gets in some how.
Do some research on earth sheltered homes.
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Old 01-07-2012, 04:42 PM   #6
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New Basement - Best Way to Waterproof


The wall doesn't yet exist, so I can engineer whatever I need to into the wall so that it drains everything down down the hill (above ground or below ground). I'm a bit limited on where I can place the cabin - it's actually an extention off the back of an existing small cabin (2-story, no basement).
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Old 01-07-2012, 04:50 PM   #7
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Quote:
Originally Posted by mjp24coho View Post
The wall doesn't yet exist, so I can engineer whatever I need to into the wall...
In addition to the other comments consider terracing the slope some too.
Two or even three smaller walls going up the hill will provide some nice outdoor space for gardens and such.

Your other statement implies you don't have enough room to build on this site.
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Old 01-07-2012, 05:04 PM   #8
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New Basement - Best Way to Waterproof


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Originally Posted by mjp24coho View Post
The wall doesn't yet exist, so I can engineer whatever I need to into the wall so that it drains everything down down the hill (above ground or below ground). I'm a bit limited on where I can place the cabin - it's actually an extention off the back of an existing small cabin (2-story, no basement).
I would engineer at least a 100 year flood drain for that retaining wall considering what the use is for along with terracing as mentioned.

What is the slope and height of that retaining wall?
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Old 01-07-2012, 05:19 PM   #9
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New Basement - Best Way to Waterproof


The retaining wall will be around 6' tall and 70' long. I believe teh hillside above it slopes at around 1/6 (1' of drop for every 6' of distance).
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Old 01-07-2012, 07:01 PM   #10
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New Basement - Best Way to Waterproof


There are a lot of "contractors" in my area with varying skills, so you are smart to try to learn all you can. That's why I've been reading here a lot (thanks, guys). I don't know if my experience will help you or not, but I will say water could be an issue for you. I'll also say from other places I've had a basement and upper level, that having a cool basement is great in summer as is the upper level in winter.

I bought a cabin on a similar lot 4 years ago. The back of my basement is completely underground and the front is a walkout, so it's a steep hill. There is a timber retaining wall 6-10 ft from the back wall. I wouldn't buy the cabin again due to the lot, despite my great loft that feels like a tree house.

I never met the previous owner so don't know actual history of house, but at closing, I was given a piece of paper that was a B-dry gravity french drain system warranty. I've not had any standing water in the basement, but have a water/icing issue in the drive and turnaround next to basement that I've spent $$ on but haven't completely fixed. I'm seasonal and 2 summers ago, when I returned there was mold on cardboard boxes that were on the basement floor. I think/hope it was condensation since it was a hot summer and I had air off. This past summer, I left air on 85 and had no mold. I didn't leave cardboard on concrete either.

In addition to the interior drain, there are black pipes along edge of house, at least on the sloping sides. I'm not sure what's at back. If anything (and I think there is), it's buried.

I believe the previous owner had a significant water problem. The house was built in 92 and a b-dry french drain system was put in in 1998. I obtained info recently from b-dry and it indicated the owner had to remove sheet rock (none there now) and after I started looking, there is a post that had a water mark at base. sure I have bids to have the basement finished, but i waited to make it's sure dry and will have the b-dry rep come check the system before we build on it.

Two other comments. You can put walls on top of the systems, but can't nail into them-have to use liquid nails. Took me a while to find that out. Also, one contractor said there should have been a concrete retaining wall around back of house.

Good luck with your decision. Could you make the basement a little smaller so it's not so close to hill?

Last edited by canoes; 01-08-2012 at 12:06 AM.
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Old 01-08-2012, 11:34 AM   #11
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New Basement - Best Way to Waterproof


A 6' retaining wall stretching 70' long will not be cheap ($10's of thousands) and probably requires a permit including engineering to spec. 1:6 slope is not a big deal with most soils. Solid clay could pose a risk though because of the water weight. Definitely terrace. Where I live two 3' walls do not require a permit and are a much smaller load together than what a 6' wall would be.
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Old 01-08-2012, 03:53 PM   #12
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New Basement - Best Way to Waterproof


This is all very good advice, and gives me a lot to think about. Thanks everyone for the responses.
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Old 01-10-2012, 10:53 AM   #13
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New Basement - Best Way to Waterproof


If the basement is adjacent to the wall, the way it's shown in the diagram, then you'd really be building a 6' wall on top of an 8' wall. You definitely cannot do that without an engineer. Essentially you're going to bury a floor and a half.

As far as the water proofing, I've seen two of those jobs done recently. Basically it goes like this:

Install a french drain at the level of the footer.
Pipe the drain to daylight.
Spray black plastic goo on the block.
Install a plastic drainage mat over the goo.
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Old 01-10-2012, 09:09 PM   #14
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New Basement - Best Way to Waterproof


prior to backfilling the excavation, slather on a good coating of asphaltic fiber-reinforced roofing cement & protect that w/a layer of ( miradrain/delta drain) - install a toe drain in a properly filtered stone trench which would allow the pipe to drain to daylight as you posted,,, backfill in complacted ' lifts ' & grade the surface accordingly,,, probably would have to move your retaining wall back so that could be built on firm soil including piers sunk to the drain's level,,, this is going to be tough work w/o good access but it is ' doable ' - you may wish to reconsider the full bsmt idea & only have a partial for better longevity
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Old 01-11-2012, 06:06 PM   #15
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New Basement - Best Way to Waterproof


I'd build some drains just in case, but I'd also suggest some basement sealer. I can't remember what it is called but it is black and you paint it on with a brush. Since using it in my own basement I haven't had any problems and it stays a lot warmer during the winter months down there.

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