Cob: Re: Thermal Mass and R-values

[alexander neumann]

Howdy Y´all, 

I thought I´d add in all I know once again, quoting from the german
state-of-the-earthbuilding-art book "Lehmbauregeln" which is "as is"
supposed to become the new DIN.
1), Vermiculite/Perlite/whatever in cob makes so-called "Leichtlehm", in
contrast to straw-lightclay it is called mineral lightclay, but that
doesn´t change the given R-values, which are defined by the density/ weight
per volume. Lightclay is not supposed to be loadbearing.
Wellerlehm, which is somewhat similar to cob has a density of about 1500 to
1800 kg/m³, which gives an insulation value of 0.7 to 0.9 W/mK, Lightclay
of 600 kg/m³ which is ,believing earth-guru Gernot Minke about the best you
can get in real life, has 0.17 W/mK. 
In comparison, regular fibreglass or cellulose has 0.04W/mK, so, an 8inch
insulated stick frame wall is more insulating than a 3feet cob wall.
So, personally, I don´t think additives to cob or socalled leichtlehm are
getting us anywhere.

2)Insulating on the inside is something that makes me nervous, it´s very
hard to avoid thermal bridging. 
People who dedicate their life to renovation of old german timberframe
houses said they wouldn´t dare to put more than 4cm/1.5 inches of
insulation on the inside of the wall. 

3) I did not suggest cob in itself is illegal in germany, though you might
have a hard time, but uninsulated walls are illegal.

4) I don´t think insulation is that of a new idea, as traditonal thatched
roofs common in northern germany still meet modern insulation requirements.
People will also have noticed that wood is more insulating than stone, so
that wood is the material of choice in northern regions which happen to
have wood left.


So much for this weekend,
yours, Alex