Your thoughts on my basement plans

[EddieWalker]

My goal for some time next year is to build an addition onto my house that will include a 16x16 basement that will be used for storage and when needed, a storm shelter from tornadoes. I don't feel it is practical or even possible to install a drainage pipe under the basement because of the gradual slope of the land and everything that I have built downhill from it's location. While not impossible, it's a bigger job then any other part off the addition with a ton of clean up, replanting and some rebuilding involved.

My thought is to dig the hole with my backhoe, then line it with a rubber, water proof membrane similar to what is used in koi ponds. Then pour the floor right on top of the rubber membrane. Then build up the inner walls with 3/4 plywood and brace it all up against each wall without any forms on the outside, just the same rubber membrane up against the dirt walls of the hole. Then pour concrete into the wall cavities and when dry, remove the bracing, but leave the plywood for interior walls.

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.

 

[TCJatko]

How about some kind of drywell to channel the water away and let it percolate into the soil at its own pace?

 

[SirReal63]

What is the life expectancy of the membrane?

 

[EddieWalker]

In my experience, any sized area under the slab that I put gravel will fill up. I received 6 1/2 inches of rain two days ago, and inch and a half yesterday and another inch today. This is extreme, but it's not uncommon to get 3 inches out of a heavy storm here.

I'm searching online for different types of pond liners and roofing membranes. Some have 30 year warranties, and they are designed for exposure to the sun every day. I'm wondering if it would every break down buried in the ground?

 

[GPintheMitten]

I would put in a subpump. Run a generator if necessary but leave it outside with an extension cord to the inside.

My subpump has an auxiliary 12 volt pump with battery and trickle charger.

 

[bigtiller]

My 2¢ worth says to make a plan for removing water. With my luck, some time, some how, it will spring a leak and there will be water down there. Maybe a dehumidifier will be enough to collect it before it becomes a problem.

I am sure you have thought of this, but why not build the storage/storm shelter above ground, close too but separate from the house?

 

[EddieWalker]

Yes, we did consider other locations, but when two tornadoes hit less then ten miles away last year, nothing above ground is going to be safe. The question becomes how far do you want to have to go to get to it during a heavy storm at night? My thinking is that if we are going to build one, it should be close enough to not hesitate getting into it. Then there is the added advantage of using it for storage.

There are some 45mm EPDM pond liners from Firestone that are claiming a lifetime warranty and I've found some 60 ml roofing EPDM liners with 20 year warranties that should be stronger, and even some 90 ml sizes.

If I overlap my seams by 2 feet and glue them together using the best glue I can find, I don't see why this wouldn't work.

In every example of water proofing a basement that I can find, they are all about shedding water down the walls to a collection area under the basement, then removing the water by either gravity drainage or electric pumps. Why doesn't anybody just make the entire hole in the ground 100% waterproof?

 

[GPintheMitten]

Yes, we did consider other locations, but when two tornadoes hit less then ten miles away last year, nothing above ground is going to be safe. The question becomes how far do you want to have to go to get to it during a heavy storm at night? My thinking is that if we are going to build one, it should be close enough to not hesitate getting into it. Then there is the added advantage of using it for storage.

There are some 45mm EPDM pond liners from Firestone that are claiming a lifetime warranty and I've found some 60 ml roofing EPDM liners with 20 year warranties that should be stronger, and even some 90 ml sizes.

If I overlap my seams by 2 feet and glue them together using the best glue I can find, I don't see why this wouldn't work.

In every example of water proofing a basement that I can find, they are all about shedding water down the walls to a collection area under the basement, then removing the water by either gravity drainage or electric pumps. Why doesn't anybody just make the entire hole in the ground 100% waterproof?

Maybe because no one has found a 100% effective cost efficient way to do it. Too much potential in all the seams for water to enter.

 

[EddieWalker]

Good point. I'm also worried about wear, or friction over time. Actually more worried about that then I am about not getting good seal, I think that's pretty easy to do, it's what happens long term that has me nervous.

Looking at the different websites, 24ml EPDM seems pretty standard for the walls of basements. I wonder if that ever wears through from movement in the soil?

 

[4570Man]

My basement doesn't have a drain. In HEAVY rain sometimes the walls get moist, but water had never puddled up.

 

[GPintheMitten]

I think there are several problems with the plan. No forms on the outside will waste a lot of concrete. Leaving plywood against the concrete will hold moisture that could lead to mold. The 3/4" plywood will be expensive. I would pull it and reuse it for the floor or other uses. Might actually be cheaper to rent forms but I don't know the cost of that.

I'm all for innovation but I think in this case, I would go with more tried and proven methods

 

[Billrog]

Eddie if you build it like a reservoir you should have not problems re-enforced water proof concrete.Pour the floor first with a seal you can buy the goes in the floor 3" under wear your building the wall and it sticks up into the wall. If you go with forms there are plastic form ties for that purpose no rust or leaks around them. 6 mill poly under the slab wouldn't hurt. Sounds like you have clay so no gravel it creates a place for water like you said. If the ground is clay and sloped away from the building no water is going to permeate the soil and cause problems. As long as the water table is lower than the floor there's no hydraulic problem. I'm sure if you look on line there will be a company that sells quality pond liners that you buy the roll then weld the seams together. I worked on one job where the liner for a reservoir was 300' x 300' -30' deep sloped sides and they chemically welded all the seams together with some kind of glue.

 

[Deere Dude]

I would put in a subpump. Run a generator if necessary but leave it outside with an extension cord to the inside.

My subpump has an auxiliary 12 volt pump with battery and trickle charger.

What about tiling around the rubberized wall and have a sump pump outside in a pit. Even if a rubberized wall could leak, wouldn't all the water along the wall go straight down into the tile, then to the submersible sump pump?

 

[Deere Dude]

My goal for some time next year is to build an addition onto my house that will include a 16x16 basement that will be used for storage and when needed, a storm shelter from tornadoes. I don't feel it is practical or even possible to install a drainage pipe under the basement because of the gradual slope of the land and everything that I have built downhill from it's location. .

I am also concerned with tornadoes and live in a place where the water table is high. Our answer was to build an above ground unengineered storm-shelter. The floor has 1/2" rebar crisscrossed in 8" of concrete. The rebar at the ends were extended a foot or so and cemented into the garage wall and the floor. Th rebar verticals were welded to the floor rebars and the rebars in the ceiling were welded to the wall rebars. Everything, the floor, walls and roof were 8" of concrete with a steel door. The shelter is 8x8' and only has a bunk-bed and a chair and shelves for stuff. It is not for storage but easy to get to and dry. Then around the shelter we built an addition to the garage so the shelter is in the corner and all is high and dry.

I have seen plenty of shelters standing while the houses are totally gone and I am hoping I never have to use it, but I would feel comfortable with it.

 

[jk96]

Eddie I see a lot of problems many of them mentioned. Let me ask this. What happens if your plan fails? What is the fix and cost? The answer to that may be enough to persuade you one direction or the other.

 

[MossRoad]

Couple concerns...

If you built it water-tight and you ever get a high water table, big rains, unknown water source underground, etc... it'll float up out of the ground just like a boat. It happens to one-piece swimming pools sometimes when people drain them. It happens to burial vaults in cemeteries. It happened to our town's sewage plant when they were building it; giant cement tank probably 100x100x20 lifted out of the ground several inches. My father was an architect. He told me several stories about watertight basements lifting entire houses and buildings up out of the ground due to ground water issues. Just something to keep in the back of your mind.

Around here, they put a drainage tile around the inside and the outside of the footing. The inside one goes to a sump pump. The outside one goes to the inside to a second sump pit (can't figure why they'd want to bring outside water inside, but that's what they do, if there's no way to gravity drain them).

There's usually waterproofing on the outside and a foot or so of gravel down the entire depth of the outside wall, usually in filter cloth, so any water that may come up against the outside wall will drain fast down to the drain tile, into the sump pit and be pumped away.

On the inside they never put wood sheeting up against the interior concrete wall. With the cooling and heating of concrete, it attracts condensation. The wood may rot or mold, as others have mentioned.

 

[EddieWalker]

Good point on the wood. I've left it on forms before for quite awhile and never noticed any problems. It seals up air tight, which is what I was thinking would happen when pouring the walls. I can go either way on that, I was thinking it would be nice for hanging stuff on the walls, but I don't really plan on decorating it and will just use plastic shelves for storage, so I'm kind of at a loss as to why I want to have wood on the walls.

If I go with a pump, then I will have to dig a hole in the floor. I cut through concrete all the time for bathroom remodels that I do, so that's not a big deal. It would be easier to just form it out and I might do that. If the rubber liner works, I wont have to remove the concrete and it won't matter if there is a 2x2 area framed out. Then it's just a matter of cutting the liner and digging a hole for the pump. I'll have everything wired anyway, so I guess if my idea fails, the worse case scenario is that I have to buy a sump pump.

 

[GPintheMitten]

Why cut concrete for a sump? That makes no sense to.me. Dig the basement, Form for footings with a few places to connect outside tile to inside tile. Pour your footings, then form for walls. Pour walls. Put tile inside and out and run tile to a crock that you set before you pour the floor. Then pour your floor. Done.

 

[EddieWalker]

There wont be any drain tile

 

[GPintheMitten]

There wont be any drain tile

Really? Do you need a building permit? You better check with your building inspector. I always thought it was code but perhaps it is not. Maybe it's just a best practice approach.