Cob: Windows & walls

[John Schinnerer]

Aloha,

-----Original Message-----
From: Kelly, Sean [mailto:SKelly at PinpointTech.com]

Production double or triple pane windows typically don't have an actual
vacuum between the panes (at least not the kind of windows the average
homeowner/builder can afford!).  They have air, or in some cases inert gases
(to lessen condensation potential, etc.).  They insulate nonetheless because
they don't have enough airspace between the panes for convection currents to
get started (in other words, the air or gases in there can't move around
enough to significantly move heat between the panes because there's not
enough space for them to do so).  

As mentioned, I read somewhere that the space can be up to about 2" before
convection causes significant heat loss...I'll try and find that reference
sometime - I think I got it from the good 'ol Rodale "Solar Greenhouse
Book."

>What is the rule of
>thumb for height to width on cob?  

The structures I've worked on (3 different ones) and seen (another 4 or 5)
have typically had 16" - 24" base width for a 1 - 2 story finished height (1
1/2 story meaning a loft upstairs, not necessarily all full standing
height).  This gives roughly a 1:6 to 1:8 base:wall height ratio...anyone
got their Cobber's Companion handy?  I think 1:7 or so is given as a
reasonable ratio for "Oregon cob" (i.e. a careful sand/clay/straw mix well
put together).  

"Legend has it" that the old Devon 3' - 4' thick walls were a less careful
mix, often with very short straw, thus needed to be thicker...

John Schinnerer