Water tank foundation

[Seeb]

on StTomas the roof of the tank is the floor above, and if you have tile on the floor you can hide the hatch in the tile pattren

[TrevorKane]

I guess it doesn't matter much that there's always standing water under the floor when the humidity is near 100% most of the time anyway.

[Kapohocat]

quote:

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Originally posted by TrevorKane

When you use the tank as foundation, what does the 'tank lid' look like? Is it just the joists and sub-floor, or is there some other protection?

Also, do you put an access door in the floor?

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The one Pete put in for one of our clients has a round lid flush with the lanai. One time the overflow got plugged and the tank lid "popped" allowing the excess to spill out on the tile floor. We squeegeed it off and good to go. Robert did put Palisade on the house walls down a ft or so below the tank top and up the wall about 2 ft - also allows you to power spray lanai with out worrying about water getting into house under siding.

[TrevorKane]

So, can the tank walls also serve as stem walls for the joists to sit on, or does that end up costing more than it would save?

[john the architect]

I do include vents in my tank designs. The overflows are also air vents. These are made to let water out, block insects and trap most light.

I have only gone two floors plus a loft over a tank so far structurally.

I don't use joists or precast panels for the floor, and I found a very good way to seal the floor hatch. I have one in a kitchen and nothing gets through to the tank.

Our home in HPP was permitted with a waste line run above a water tank. That particular tank was a spare which we have not yet put into use (it may become a music room or some other bulletproof space). We also have waste lines that are over the living room ceiling. Theoretically either could leak but not very likely.

Ideally waste lines have routes that do not require cutting through major structure such as a concrete tank lid. Remember my initial post: the floor is another system built above the tank lid.

The water that is drawn from the tank goes through three filtrations plus a UV sterilization,
so the tank is not required to be a sterile environment. I do enjoy that a properly designed tank (including the collection system) resists sediment build-up for many years.

People always talk about how they think tanks are ugly. Houses set on the ground are less secure and receive less of the tradewinds to keep them cool and airy. A heavy foundation is required to keep you grounded in high winds. The obvious solution is to put a tank under some part of your living space.







John Maloney
310.562.0362
johnmaloney3@mac.com
Hawaii Architect AR8082
www.jmagreenbuilding.com
www.greenrentalhawaii.com

[MarkP]

I recall from reading the Uniform Plumbing Code years back that if you want to bury a waste line and a potable water line in the same trench they must be separated horizontally and vertically with the water line higher, so it makes sense that there might be some similar concept for waste lines and catchment tanks.

Obviously part of the kitchen described above is over the tank. Is the sink itself within the footprint of the tank? Is this house in Hawaii?

Years ago I recall seeing a report from somewhere in China where a lot of people were getting sick at this apartment building. The building had a catchment tank. Well, there was a waste line running above the tank, which apparently had no lid. The waste line was leaking into the tank. Incredibly gross thing to think about. Now I know that the problem was probably poor construction or failure to obey codes but the question remains of what our codes would say about it.

I really like the concept of the tank under the house. Does the tank extend completely under the house like an extra thick slab, or are there discrete tanks along one side?

I tend to get carried away with certain things. One of my pet peeves is what would be the best foundation to have here in earthquake country. The answer I came up with is a cellular mat foundation. Instead of one single thickness of concrete slab, there are two slabs several feet apart. The upper and lower slabs are connected with vertical walls. In large buildings the result is an egg crate type effect with usable rooms underneath, although the door openings through the walls must be heavily reinforced and kept to a minimum since the walls are transmitting the shear forces between the upper and lower slabs. Anyway, if you built something like that and did it right you would get a super strong slab that you could lift by one corner and it would have these nifty compartments that would be ideal for safe rooms, music studios, or catchment tanks, anything that didn't require windows.

Thanks