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Cob: Cold Tempsbaco@pacinfo baco at pacinfo.comSun Aug 11 14:04:09 CDT 2002
I like the folksy flavor of all the thumbnail engineering and anecdotal evidence, but does anyone know of good source for science based analysis of the physical properties of cob? I would sure like to see a structural engineer/architect join some of these discussions. My sense is that many of us value off-grid approaches and organic approaches, but the simple fact is that sharing "I did it and nothing bad has happened so far" stories can lead to some dangerous situations. I looked at a cob structure and even my inexperienced and untrained eye quickly found a structural problem that could result in a death or injury, and that was a structure that acknowledged leaders in the field had a hand in creating. BB -----Original Message----- From: owner-coblist at deatech.com [mailto:owner-coblist at deatech.com]On Behalf Of Shannon C. Dealy Sent: Saturday, August 10, 2002 10:20 PM To: Do Cc: coblist at deatech.com Subject: Re: Cob: Cold Temps On Sat, 10 Aug 2002, Do wrote: > Hello all, > I've been seeing a lot of discussion on flood plains, heat, humidity and air > flow, but I have a question on how to build a better cob house for the cold. > I live in a small town in the Colorado Rocky Mountains and it regularly > gets below zero overnight in the winter. In addition, the snow load on the Generally, for climates with continuous extreme temperatures, I would say to go with an exterior insulation wrapping the cob walls such as straw bales, and I think this is probably a good idea in your area as well (though maybe it's unnecessary for a sun exposed south wall if you get winter sun on your site). If you have good winter solar exposure, you might be able to get away with less insulation with a proper solar design. The important thing to remember with cob is that what your 24 hour temperature extremes are is completely irrelevant, what you are really interested in is things like 24 hour temperature averages, multiple day temperature averages, and what you can do to shift these averages toward your comfort zone through proper building design for your site (such as using solar gain). The temperature of the cob is not going to shift significantly over a period of one night, it may take days or even a week or more to really shift the temperature of uninsulated cob. How long it takes to shift it by some arbitrary amount is a complex interaction of various factors including: wall thickness, straw content of cob, average temperature difference between the wall and outside air, air pressure, humidity, and average wind speed, not to mention any thermal gain you get during the day from sun exposure > roof would be very heavy. (A good winter will see a couple of feet on the > ground at all times). Are regular cob walls strong enough to handle this > snow load (it seems they would be). Does anyone have any experience or > advice on this? How do I keep it warm in the winter and cooler in the 90 Properly designed and built cob walls should easily handle the weight of many feet of snow on your roof, though depending on the design of your building and roof system, you may need some kind of a top plate/bond beam on the top of your walls in order to evenly distribute the weight of the roof supports since extremely heavy point loads on a cob wall can cause problems with cracking at the point of load. > degree summer weather? And since the summer days are 90 and the nights are > 40-50, is there something I need to consider with that extreme temperature > difference? What other things would I need to keep in mind? Actually, for your summer temperature swing, plain, uninsulated cob sounds ideal, since the temperature of the cob tend towards the average temperature which it sounds like would be around 65 to 70 degrees. Of course for year round temperature control, you will probably need to go with insulated cob unless you can reliably capture enough solar energy in winter to maintain your building temperature, without causing significant solar gain during the summer. Shannon C. Dealy | DeaTech Research Inc. dealy at deatech.com | - Custom Software Development - | Embedded Systems, Real-time, Device Drivers Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications or: (541) 451-5177 | www.deatech.com
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