SB: straw clay R value

[*Lootvik* <lootvik@usermail.com>]

Okay, I did the legwork from the "topping off the walls" thread:

·       Subject: SB: re: Straw/Clay Thermal Characteristics
·       From: (Robert W. Tom)
·       Date: Tue, 22 Apr 1997 16:38:36 -0400 (EDT)

on Tue Apr 22 1997
Scarecrow@lerc.nasa.gov (Mark A Hoberecht) wrote:
re: Straw/Clay Thermal Characteristics

 >    This information comes from one of my German reference texts,
 >    Lehmbau-Handbuch (clay-building handbook) by Gernot Minke.
 >
 >       density (kg/m3)         conductivity (W/mK)
 >
 >               300                     0.1
[ many in-between numbers <snipped> ]
 >               2100                    1.4
           ========================================

Thanks Mark, for those lovely numbers which will save a lot of people a
lot of frantic figurin'.

And the following conversion factors are:

      lbs per cubic ft = kg per cubic metre
                         ------------------
                            16.02
and

      Btu-inch/hr-ft^2-degF x 0.1442 = Watts/m-degC
                          (units reduced from watts-metre/metre^2-degC)

      or

      Btu-inch/hr-ft^2 =   W/mC
                          ------
                           0.1442

(I'm pretty sure that Mark meant "degrees Celsius" and not "degrees
Kelvin", or the Germans spell Celsius as Kelsius ?)

And to save John from having to do some arithmetic,  a straw/clay
mix of 300 kg/m^3 density (18.72 lbs/cu ft, which apparently uses less clay
than Sunny John's Attic Insulation recipe)  would have (according to Herr
Minke) :

      a thermal conductivity   k = 0.69 Btu-inch/hr-ft^2
            and
      an R-value of 1.442 per inch. (about the same as
                                    low-density particleboard)

and for the most dense mix of 2100 kg/m^3 ( 131 lbs/cu ft )

                k = 9.7 Btu-inch/hr-ft^2
                R = 0.103 per inch. (about the same as dense clay brick)

Given that much of the insulative value of SB is due to the trapped air
voids between the straw fibres and that with straw/clay mixes, those
insulating air voids are replaced by conductive earth, thus lowering the
insulative value,  Herr Minke's numbers seem quite reasonable.
                          --- * ---


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