Your thoughts on my basement plans

[CCWKen]

That's why you don't find many basements in Texas. People don't know how to build them down here. Forget the pond liner unless you're building a pond. If you get more than a 1/2" of rain a year, you're going to be sorry you didn't install drain tile and a sump pump. As already mentioned, 12v pumps are available and stick with the proven method of building basements. Or build a crawl space.

Added: More important than the water table in Texas is the back fill. It must compensate for the shrink and swell of the ground. If you just back fill with dirt, your basement is going to collapse. Or pop-up out of the ground like a field stone. Get someone to build the basement for you. It will be cheaper in the long run.

 

[BitChin1]

What is wrong with this idea? By not having any sort of drainage, I'm thinking that I'm sort of doing the exact opposite of a swimming pool. Whatever moisture that does work it's way down into the soil next to the basement will just remain there and not have anywhere to go, which in my thinking means more runoff. Gravel is good if I have drainage to carry the water away, but if I don't have a way to get rid of the water, then all I am doing with gravel is creating a storage place for water.

I thought about a sump pump, but we lose power all the time during severe weather, and I hate the idea of running a generator if I don't have to, especially in a small space that will require outside venting.[/QUOTE]

Eddie I have several concerns with this plan and a couple questions:

First what is your soil type and how well does it drain/perk?
How tall (deep) do you plan the walls to be? Texas is getting a lot of rain this weekend and if the soil does not drain well you would have a lot of water pressing against this wall!

As described you will have a form on the inside but not on the outside? Just using the side of the excavation to form the outer wall? I think this will be challenging to dig precisely enough to maintain typical concrete wall width of 8" - if wider that may be "ok" but concrete is not cheap! Also most of the walls strength (ability to support the load above and to resist the pressure of the dirt and water from pushing the walls down) comes from rebar grid - how do you plan to install this grid and hold it in place during the pour w/o the exterior forms? Also the interior forms can't be used as this would penetrate your liner.

Once you remove the bracing how do you expect the plywood to remain in place?

I'm not sure but do you have any "frost heave" in your area? (I don't think so) - the rough walls you may end up with would be great leverage for the frost to move the walls.

Assuming you can solve the above I think the liner could be expected to last (with no UV) but any hole will leak water into the basement area - maybe ok for temporary use area but you should plan for some means to remove water that does get in. I think expecting to seal seams will be relatively easy for liner laid out flat but if working on vertical sections or the wall/floor intersection this will not be easy to get "perfect" - anything less than perfect and you have a swimming pool vs a basement.

That said I know of company's that provide concrete storm shelters that they place into the ground - maybe you could get something prefab'd - I doubt it could be 16' x 16' though

 

[Rustyferrious]

I have no idea what the water table depth is in your area, but if it is higher than the floor of your basement, even temporarily, you may need to consider buoyancy. Storage tanks and other completely sealed structures can actually "float" out of the ground if the water table is higher than the bottom of the structure. Your proposed design is basically a boat floating in dirt. If the tide comes in, the boat is going to float up with it.

 

[/pine]

... Why doesn't anybody just make the entire hole in the ground 100% waterproof?...

Like others have mentioned...if there is no place for the water to go and the ground is saturated...it will try to "float" (displace) whatever is in the "hole"...

My suggestion is to spend a few bucks and find a local engineering/architecture grad student that thinks outside the box to review your current plan and see what they say...

 

[dstig1]

Wow, Eddie. I'm going to go with "bad idea" here. First thing I read the title and said to myself "basement?!?!? in Texas?!?!?!" Now I see why, and it is a good reason, but your execution is all wrong. You are a contractor. You know the #1 rule of water and buildings. It is not "if it leaks" it is "when it leaks".

EPDM roofing is also not exposed to the sun/UV. It is covered by ballast (stones) that help hold it in place and protect it from the sun. So you are putting it underground - same situation as a roof, and it doesn't last forever there either. Your assumption there is incorrect.

One of the main reasons for a footing drain is not to drain anything. It is a pressure break for water. If the water in the soil goes into a 4" footing drain, it kills the hydrostatic pressure trying to force it into your basement. Often times, even if it sees no daylight, it will work as it kills the pressure and allows any water that gets in time to percolate into the subsoil. Local soil conditions vary a lot and maybe this is not true for you, but it is a common condition here.

The floating mentioned is a big issue. Seen it around here on places that want deep basements next to a big lake. Bad hoo-doo.

If you are going to build a basement, just build a basement, and don't try to screw around with short cutting it. It ain't that hard to do the normal way. And given the slope issues you noted, put in a sump basket (seal it to the poly under the slab) and pipe it out to daylight somewhere appropriate with a pump in place. Use Form-a-Drain for your footings, and tie the inside and outside together so you can pump it out. Yes you have to keep an eye on a sump pump, but add a warning sensor to the system to be safe. Water always wins.

 

[Streetcar]

Like others have mentioned...if there is no place for the water to go and the ground is saturated...it will try to "float" (displace) whatever is in the "hole"...

My suggestion is to spend a few bucks and find a local engineering/architecture grad student that thinks outside the box to review your current plan and see what they say...

Be wary of getting advice from architect , they are generalist . They are slightly trained in many things.
As others have said, a watertight basement is a boat. Water will try to lift 62.4 pound of material for every cubic foot of basement .

There are battery backups for sump pumps. It is cheaper and easier to plan for water in basement, than to fix the problem after it occurs.

 

[jimmyj]

Hi Eddie. I would be doing something similar if there was that sort of tornado danger here. Scary stuff.

I don't know about Texas climate but here are a couple of youtube vids on how it's done around here. Basically there is a footing first and wall pour the walls on top.

https://www.youtube.com/watch?v=N_akSziGAH4
https://www.youtube.com/watch?v=XDeWeb6ttbI
https://www.youtube.com/watch?v=EcNodWLKBEw

Around here they use rebar rods or bolts coming up out of the top of the footing to tie the side walls in.

I hope these have some helpful ideas in them for you. These are the first 3 vids but this guy has more after these.

 

[EddieWalker]

No code, no permit and there is no building inspector anywhere in Texas outside of city limits. There are also very few basements here because there is no front line. Soil quality is what dictates foundation design and depth of footings, I'm fortunate in that my red clay is about as good as it gets for building on.

I'm also about 30 feet above the water table, so there is no worry about hydraulic pressure pushing the basement out of the ground. I know a few swimming pool guys and I've heard the stories and seen a few pics of how that happens.

My thinking is that by pouring the walls and using the dirt as the exterior form, there should be very little water that gets down into the ground. The building location is high ground that slopes away gradually. I do not believe it's possible for there to be standing water around my house, or for run off to go towards my house.

One thing that I question is if people didn't use rock and create drainage under their basements, or foundations, or anywhere, would water still go down there? By creating the drainage, you are inviting water to those locations. Kind of like putting gravel under a fence post. If you do that, then water will sit there and remain wet for extended periods of time. By compacting and filling the void around the post, very little moisture gets down there and the posts lasts forever.

I'm still thinking on this, but from all I'm reading online, it's a direction I'm leaning towards.

 

[riptides]

Why take that chance with water? Adding drainage is a lot cheaper that having the foundation lift up, or the possible repairs due to cracks and seepage.

As for possibilities of water, tough call. The water table may change for the worse. Who knows that for sure?

Even just a little water over time changes things.

 

[EddieWalker]

True, the what ifs are what has my brain spinning.