[Strawbale] R value of light straw clay

[Peter van Balen]

Minke (clay expert at University of Kassel, Germany) cites density figures 
similar to the ones given by Rob Tom: i.e. lightest, possible only in 
theory, 300 kg/m³; lightest, only possible with very careful preparations, 
500 kg/m³, but in building reality even this will compact to at least 700 
kg/m³. For such a 700 mix he gives a lambda of 0.21 W/mK (which you'll have 
to convert to your own non-metric R-value yourself I'm afraid).

Peter van Balen
France

===================

From: kim thompson <shipharbour at ns.sympatico.ca>

Hi Rob et al,

I was interested in the stats for light straw clay that were
mentioned in the  thread
Re: [Strawbale] Breathability of Wood Shakes and Roofing Felt
Can you tell us where those stats and the later R2-3 that Andrew
mentions come from.

Developing simple language to describe both production of the
material, and installation seem critical in nudging forward best use
of it in our buildings.

Thanks.

Kim Thompson
Nova Scotia, Canada

==============================

From: "Rob Tom" <ArchiLogic at yahoo.ca>

That being said, I do wonder if the cob is providing any appreciable
insulation value at what is a critical area (gable ends) WRT building heat
loss.

ie At the lowest density possible for a straw/clay mix (~300 kg/m^3 (or
~18.7 lbs/ft^3), where the straw is just barely coated with clay and
lightly placed (a mix that would be suitable for use in an attic) the
R-value is about R-1.44 per inch.

For a mix that would be suitable for a wall application, the density would
probably be closer to 40 lbs/ft^3 (and quite likely more), so the R-value
would be something like R- 0.7 per inch or less, meaning that for a cob
thickness formed by 2x8's, the nominal R-value would be something like R-5
or less, before accounting for the thermal bridges created by the 2x8
studs which would further lower the effective R-value of the wall,
depending upon the stud spacing.


> ===* ===
> Rob Tom
> Kanata, Ontario, Canada
> <archilogic at chaffyahoo dot ca>
> winnow the chaff from my edress in your reply
>