[Greenbuilding] cistern questions

[John Salmen]

Concrete tanks make a nice support for an independent outbuilding as the
wall designs are great as a prefab foundation and the loads are well
distributed (like a boat). I've used quite large 5000 gallon tanks for
outbuildings and the loads were roughly 4-500 lbs per sq. ft. (if memory
serves) which is not significant compared to standard footings and the depth
of the tanks is well below frost line. They can be insulated on the exterior
but because tanks rely on the side soil support to some degree the
insulation would have to be rigid with a decent density or if no insulation
is used the backfill should be able to compensate for expansive soils but
still provide support - foam board is actually great for that purpose. You
can typically get stonger tank lids (drive on) but they are not really
necessary for that.

In terms of aesthetics the generally round access lids are not the nicest
detail in an interior floor. You can get some cast iron lids that have a
certain charm or have one custom made that look better than the typical
plastic ones. 

There is a fengshui thing about being over water - but I think a large part
of the world lives over water quite happily.


-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of RT
Sent: August-02-12 9:40 PM
To: Green Building
Subject: Re: [Greenbuilding] cistern questions

On Thu, 02 Aug 2012 10:48:54 -0400, Sacie Lambertson
<sacie.lambertson at gmail.com> wrote:

> 1.  Cisterns in this area are built by the same people who do septic 
> tanks, ie of concrete.  Could I use such a tank to support a room above?

Without crunching any numbers first to confirm, I'd say "Yes".
It'd be a matter of designing the reinforcement.

> do I need to worry about insulating the walls of a cistern? ie there 
> would be room for expansion.  Freezing is normal in our NE Kansas 
> winters.

I'd say "yes".

Some years ago one of my neighbours exposed the upper portion of an end on
his septic tank. (I forget how or why. I think that it had something to do
with a landscaping and/or deck and/or pool project.

The septic tank developed a nice crack on that newly-exposed (outlet) end
just below the outlet hole for the line to the weeping tile, presumably as a
result of freezing & frost expansion of the top surface of the water.  
And yes, it stunk in the vicinity of the tank.

Even though the walls of the septic tank could be made to be capable of
supporting an addition, I think that I'd surround it with a CMU stem wall,
spaced away from the tank by a minimum of 6 inches and then fill the cavity
with Roxul insulation, and tie the CMU wall back to the walls of the septic
tank, essentially making an insulated-core, double-wythe wall.

--
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

< A r c h i L o g i c  at  Y a h o o  dot  c a  > (manually winnow the chaff
from my edress if you hit "reply")

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