Cob: Cob insulation idea

[Darel Henman]

The writer of the article Myra shared with us evidently does not have a
good understanding of thermal dynamics.  I will intersperse some of my
comments below.  

Myra Bonhage-Hale wrote:
>  .................
> "Cob, however, is a mediocre insulator with a low R-value per inch.  

This completely ignores the thermal mass and its effect on heat
exchange.  Fiberglass companies like to mislead in this way to.  
Fiberglass damp from condensation or leaks and wind infiltration can
have even less insulative value than cob.


> On cool days, heat from within bleeds steadily outward.  

  NOTE 1:  Heat bleeds out from ANY kind of wall if its warmer inside
than outside.
  NOTE 2:  Heat does not just bleed out, it goes into the home, if its
warmer than the inside air.
  NOTE 3:  It provide a store of heat to keep the inside heat from
bleeing out so fast.


> To circuvent this,
It can't be circumvented.  It can only be reduced for ANY kind of wall
if there's a temperature difference inside and out.

> City Repair designed a double shell; two six-inch walls of cob sepaated by eight
> inches of insulating straw.

It would have been better to insulate on the outside and keep the mass
heat storage inside.

> On each side of the straw is a wattle wall -
> flexible sticks woven into a solid barrier-to hold back the cob.

Hold back the cob?  Cob can stand on its own.  If its waddle and daub,
then its the bones upon with the daub is glaubed into and onto.  Perhaps
they required this 8" thin non-bearing walls.

> This makes for a thick wall, twenty two inches through.
This can be done with insulation on the outside or with only cob or any
other material if desired.  Strawbale walls are about this thick after
being rendered in a soil or lime mortar.


> The roof is eually innovative.  Above two-by-six rafters salvaged from
> shipping palletes lies a polyvinyl chloride (PVC) membrane (PVC offers the
> best protection against leaks buts it manufacture produces toxins.

I don't get what's innovative about this?  I thought all roofs have a
waterproof covering.  

> Other options include liquid asphalt or a rubber membrane.)  Atop this is a living
> roof of sedum and other drought-tolerant plants which can withstand
> Portland's often dry summers.

I am convinces that living roofs, a.k.a. green roofs are a very good
idea.   Does anyone know of any non-toxic materials that can be used for
the underside as a waterproof barrier?


> Rains trickles trough the greenery, down
> bamboo gutteres, and into a set of sculptural ponds that hold water for the
> garden.  This reduces pressure on both Portland's water supply and its
> overtaxed storm-drain system.

This is Portland's "eco-roof" program.  I wish other cities and states
would catch onto its benefits.

Darel