Rethink Your Life!
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The Work of Art and The Art of Work
Kiko Denzer on Art

[Cob] Janet-windows, doors, thick walls

Shody Ryon qi4u at
Mon Dec 22 01:54:24 CST 2008

> > Hmmm, I wonder about saving money on the permit: in
> California, buildings
> > are usually permitted based on the exterior footprint.
>  With some
> > conversations with building depts., some jurisdictions
> will accept the
> > interior measurement and add the thickness of a 2
> x6"wall so that the owner
> > isn't in effect penalized for a super-insulated
> wall.
> Also,  someone  else probably already commented on this,
> but a 5' thick wall
> of cob will take a loooong time to heat up if the house
> cools for a couple
> of days during the winter.  I think you'd be much
> better off with a
> conventional strawbale or light straw clay wall and a very
> thick cob like
> plaster on the interior, and conventional clay plaster on
> the exterior.
> Then you'd have the insulation where you need it,
> outside the thermal mass.
> You might defeat your comfort level with so much mass at
> such a low rate of
> insulation.  See for the Steens'
> approach to built-ins
> with bale.
> I encourage you to use a vapor barrier between the ground
> and your floor.
> We didn't on our bathroom addition, and
>'s a colder space than
> need be because ground moisture (there is excellent
> drainage, so it's not
> that) soaks up the heat.
> Best of luck with your project.
> Barbara
Hi Barbara,
I really like your post!
I am not an expert but I think the ground tends to take 
on the avarage year round temp. Areas that have colder 
winters will have cold ground compared with what most 
people would consider comfortable. Earth has poor 
insulative value and fair thermal storage value which 
I think means that if it is not insulated external to 
the living area that it would strongly cool that area.

An alternative would be heating the floor, possibly with
air heated in the sun:
take a look at the diagram at the bottom of the page. In
this case, as usual, the foot print of the house didn't 
supply enough thermal mass, so an exterior 8 foot 
perimeter was included.

Since I like energy efficiency, I compare energy used in 
different building systems.
Granted I do not know how much is used to excavate the 
floor plus an 8 foot perimeter, as Annualized Geo Solar 
(AGS) uses. This system might work for your project.

I think it would be more energy efficient to install a 
raised wood floor with insulation in the joist bays. 
Alternately a lot of insulation could be installed 
underground using the special insulation used under 
concrete slabs.

I think the price of this insulation has increased and not
fallen like oil has. I have never heard of anyone 
installing more than R15 this way, which is too low of a
R value in many areas with colder winders, if minimal 
heating input is desired. I think more isn't used because
of not understanding or valuing "super insulation". The
idea is to spend money once on really good insulation 
instead of an on-going basis with fuel, wood, or? Also 
the cost of the insulation can add up quickly.

A super insulated house can easily have solar heat as a
primary heating system especially if thought is given 
to window orientation and if really good thermal storage 
is used a low cost ($300??) (Amcor Nanomax 12000 BTU 
Portable Air Conditioner) air conditioner can be 
vented as a heat pump and can be a low cost back up heat,
taking heat from the thermal storage and into the living 
space. Thermal storage can be used 8 different ways for 
heating and cooling in different temperatures, all with 
very little fussing.

I think the thermal attic system is the most energy efficient
system and it can be built at a very low cost. The site is 
new, so it doesn't show all the ways to use it yet. Perhaps 
you can use this info some how. The attic should have its own 
insulation envelope separate from the living space, but if you 
can not afford it, perhaps it can be planned for and built 
over time. The attic has shelves for +- 3,000 2L soda bottles 
filled with water. I suspect 3,000 might be for a smaller house.

The weight of the bottles might need to be calculated but in 
most cases it falls with in the amount a house built to code 
can hold.