Hey, I'm designing my Cob Tipi right now & have a question regarding the cob 'dome' part of it.. I havent found much helpful info searching the internet so I'm hoping to get some thoughts & insight on the matter.
Basicly I'm just building a dome / cone with a large entrance way(sort of like an igloo) out of cob & building a thick tipi structure closely around it. Kind of like a roof that covers the entire building. -The large logs & sticks etc are held by & into cob. & I'll be using linseed oil of course. -The reason for not just building a dome is not just for looks but to protect the cob from the rain, as it rains quite a bit for 3 or 4 months of the year where I'll be building it. -There is no question that this is the type of home I would like to build & live in when I move into this eco village in Northern California. -I would like to live in a tipi structure but would like the comfort of solid walls around me, rather than a cloth & some sticks. This is more of a long term home. -I'm building a fireplace into the wall & will work around the chimney, covering it's sides aswell. In the entrance way I'd like to build a small cob bench & perhaps keep my earth oven against the opposite wall, so I wont have to build an edditional structure for it. So I suppose you could say the entrance way is more of a porch area.
So at last my question is, can I do it without sandbags? - I would like it to be as natural as possible & I really dont need or have the money to go buy a bunch of sandbags.
All responses are greatly appreciated & considered, ! Thanks for taking the time
Firstly, from what I have experienced and read, you can't even begin to estimate what sort of materials or additives you will need for your cob building material until you actually start digging in the ground and have an idea of what you are dealing with.
I am not sure where you are planning on getting your earth to build with, but what I suggest doing is try to get as good idea as possible as to the consistency of your building earth that you plan to use. You can do this a number of ways, but the best way is to do a 'shake test' - which involves taking a sample of your building material, put it in a large mason jar with water, shake it, and let it settle out. This test gives you a rough estimate of the ratios of different components of your building earth (rocks, pebbles, sand, clay, silt, etc). There is plenty of information on this method out there, but if you can't find any, I can explain further.
If you get lucky, your earth won't need any additional sand, but this is rare. If you do need sand, you don't need to goto the store and buy sand. You can find decent sand in any number of places - old unused playgrounds, old quarries, craigslist, neighbor, be creative.
Teach a man to fish, he'll eat for a lifetime. Teach a man to build with cob, and he will build a home that lasts for generations.
Thanks man, That's a great idea. I'll definitly research into that & do some tests when I get there. Apparently the clay is good for building in Northen California so thats a bonus, I'm excited to check it out.
NinaRasta, Have you spent any time living in a tipi? I would just set up a tipi frame,what ever size you think will be comfortable for you to live in, the native americans had some up to 40 feet. (My lodge is 17 ft. ) Rather than using the hides or canvas covering you can continue to add poles untill you have a large wooden cone. You may have to use smaller and smaller poles. Leave the smoke hole for a chimney. I would also leave the ventilation opening all around the bottom of the cone and install a liner on the inside to maintain the upward draft that a tipi has. Then cover the wood with cob. You could still have smoke flaps and poles if you wanted, or just have a covered vent pipe. You could have a sleeping or storage loft installed too. A rocket stove would add heat to the mass if you ran the chimneys in cob mass. I have seen tipis made of concrete so I would think that cob would work too.
Hey, Yes I've lived in a tipi. Thanks for your thoughts, it's reasuring to hear that tipi's have been made of concrete The sleeping or storage loft is an interesting idea, I have to say I havent really thought of doing that in a tipi. I think I have a pretty good idea of how it would be done, but what were you thinking? & I would have to cover the cob with more wood to protect it from rain. That's why I was designing it with a full inner tipi & an outer tipi with a fairly thick layering of cob in the middle. It should be very durable aswell.
as a cob builder, I would first suggest getting your hands on the book "Hand Sculpted House". With forms you can build almost anything out of concrete. However cob is not exactly the same. There are very good reasons why people don't build domes out of cob ( they collapse) especially in rainy climates. I believe that only in totally ( meaning 100%) dry climates you can possibly achieve a dome shape with cob. If I was the one to to build a tipi out of cob I would only build 1/2 to 3/4 from the ground up with cob and then find an alternative method to finish the top. If your living in Northern California then your close enough to venture up to either House Alive or a little further to Cob Cottage Company. Both in Oregon. Well worth the trip especially to C.C.C. for some face to face with Ianto Evans. He can tell you everything you need to know.
I really like this idea. If you make any progress can you update this thread? I am going to sub it. I would start by building scale models of cob and leaving them outside to see how they fair. If you going to have a fire inside the cob teepee I would suggest you also make a way for air to enter like a teepee would.
An earth covered tipi is essentially an earth lodge. It would be prudent to use a heavy internal framework as was used by the Plains Indians for their earth lodges. Do an internet search for "earth lodge." Add "indian" or "native american" to reduce your non-relevant hits, but you will lose some interesting designs. The Navajo Male Hogan is similar in layout to a three-pole tipi, but with the poles oriented to the North, South and West with an East facing vestibule.
The earth lodges were often wrapped in a thick layer of straw before being covered with sod and/or dirt. A similar solution with some modern adjustments can be found here: http://www.thatroundhouse.info/
The Chinese developed a straw-clay silo that had a domed roof. It was very difficult to make the dome, so the design was changed to allow for a conventional roof with straw-clay walls:
China, Grain Storage Structures: Report on a FAO-UNDP Workshop Study Tour in the People's Republic of China
It won't be seismically safe, but it would be really cool. I suppose if you built it with the Chinese tamped straw-clay walls, it might be a little safer than just cob, but you would probably want to clear that with an engineer first.