My wife wants to cob a playhouse for my daughter, I want it to last, so I am doing the research I am also considering setting my fence posts in rubble instead of concrete. The rubble is said to keep water off the posts, and extend their lifetime, plus make replacement easier. Would an urbanite foundation wick water to the cob or wood that might be sitting on it? Some cob builders shy away from concrete, citing the moisture problems it can introduce as well as the invested energy, etc. I imagine the fact that it would be fragmented and not monolithic would adequately disrupt the wicking action, but I thought someone here could speak from experience.
With all my posts, please keep in mind I have one cheek still firmly in the armchair...
When the concrete is dry stacked only a scarce few points of contact join the pieces, so wicking moisture up from the ground is eliminated. Up here in the Pacific North Wet we tend to bring the urbanite stem wall up to 18" above grade, as well as the big overhang shown above.
Thanks for setting me strait! This beautiful building, how was the roof constructed? Also, does this mean a poured concrete foundation is okay? Finally, some natural builders shy away from building load bearing earthen walls. What's your take on it?
Poured concrete foundation will hold and wick moisture upwards. The better your drainage the less this effect. Any wooden frameworks (eg. sill plate) should be isolated from concrete fdn. with a waterproof membrane. Plastic foam 'sill gasket' is common. 2 layers of .6mil poly can do in a pinch. Some people say that laying a sheet of plastic around the bottom and sides of the footing makes the surface smoother and thereby closes the pores to reduce water infiltration.
Whether or not to bear a compressive load on a wall depends on many factors. Light clay walls need a wooden (or equivalent) frame to carry compressive loads. Strawbale usually the same - although some people get into compression wrapping it in metal mesh to handle compressive loads. Adobe works fine for non-seismic zones. Monolithic Cob bears compressive and shear loads just fine if it is thick enough.
There is a lot of grey area between the techniques… and ways to boost sheer strength with burlap mesh and various reinforcement materials. But that is my basic sense of it.
The roof is a tension structure. Fir-pole framing, curved in all directions with plywood forced down over it. VERY light construction but also very strong. Waterproofing is supplied by pond-liner, cardboard layers under to protect and provide some insulation (don't need much in my climate), wood-chip duff over the top to protect from UV. Relatively inexpensive and long lasting (pond liner rated at 30-50 yrs).
I'm playing with ideas to create a system without using a stone (urbanite) foundation AT ALL. I'll probably build a tiny test structure this season. Cob directly on the ground with earth-works to keep away water. I know that conventional wisdom screams not to do this but I don't care! Just a few years ago, conventional wisdom said that Rocket Mass Heaters shouldn't work. So much for that. I know of one 300 year old cob building in Devon, England that is cob straight on the ground. Also, all over Africa, the Mid-East and the Far-East. I have historical support! All that's left is to figure the right set of procedures.
this image shows a 500 year old cob cottage, also in Devon, UK.
In my experience choosing your site is key to a successful cob on the ground structure - as is having a large overhang on the roof with a french drain dug in around the structure where the drip line from the roof occurs. Many coats of limewash are needed on external walls prone to wetting from wind driven rain. No reason why it shouldn't last for a very long time.
The cottage in the image has had several additions over the years including a stone/brick and cob extension on the left as you are viewing it and a stone "plinth" around the base, the buttress on the right may be an addition too. The buttress shows wear consistent with splashing caused by passing vehicles.
On a sobering note a cob cottage collapsed not far from there, www.dailymail.co.uk/news/article-2743018/400-year-old-thatched-cottage-picturesque-Devon-village-collapses-road-renovation-work.html the blame was put on the cob wall failing ( this was the reason given by the renovation company who were working on the building at that time ) Close examination of the photos show that at least three walls of the building had been faced with brick and a brick extension had been added by keying into the brick facing - imho it was the brickwork that failed and pulled the rest down with it - all cob buildings that I have seen are much wider at the base and get progressively narrower as they grow in height - hard to see how they achieved a perpendicular brick facing on that kind of profile without either massive infilling at the top or large voids ...
apologies if I haven't got the link thingy right - I need my grandchildren to give me more lessons on my umputer
Post by matthewwalker on Apr 22, 2016 16:50:39 GMT -8
Hey Kirk, care to do a new thread and elaborate on your roofing system? I get the structural part, enough.....but I'd love some details on your epdm or whatever roofing membrane and attachment/drainage systems. One particular question is how shitty of a liner would you accept for this application? Do you go right to the 45mil rubber or other higher end stuff?
Thanks man, pondering some options for my summer projects.
TexasGonzo: Sooooo glad I found this site! Its always rewarding to find such a super group of folks! To any and all, feel free to PM me anytime. Thanks for having me!
Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
Mar 26, 2019 8:19:28 GMT -8
michaelegan: i am unable to open the sketchup files on my mac. I used sketchup a few years back but apparently the company now requires a subscription. does anyone have any advice/instructions on how to use the program or how to view pictures without spending money?
Aug 20, 2019 18:41:48 GMT -8
mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
Aug 23, 2019 13:33:44 GMT -8
topbaza: hi everyone, been searching all over net and this is were i need to be i think!!
Sept 28, 2019 6:16:25 GMT -8
anounaki: Hi, why I cant upload photos when I make new tread to this forum?
Feb 28, 2020 2:09:40 GMT -8
ahansen: photos under 1 mb not possible?
Jun 4, 2020 0:09:21 GMT -8
belgiangulch: Photo's are possible. They must be downloaded elsewhere and the image url (adress) is copyied.
Sept 14, 2020 7:26:15 GMT -8
belgiangulch: While creating a thread click on the small picture in the banner above the reply. A box pops up, paste the image url in the box. Pay no attention to the huge list of numbers and such.When you finish and hit reply your post with pictures will come up.
Sept 14, 2020 7:29:27 GMT -8
deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
Oct 21, 2020 6:53:59 GMT -8
BenAlexanderT: Happy new year everybody. I wish you the best
Dec 31, 2020 15:06:14 GMT -8
Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
Jan 16, 2021 21:54:43 GMT -8
gnomedome: i realsie this is from 2009
Apr 14, 2021 8:30:44 GMT -8
gnomedome: i realize this is from 2009 id love to see the photos from this ..as im looking to build a sauna soon similar to this .... if anyody sees this post email@example.com..... the photos in this post did not show up
Apr 14, 2021 8:32:00 GMT -8