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Need help with cob roundhouse plans!  RSS feed

 
Huw Grant
Posts: 2
Location: Abergavenny, Wales, Uk
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Hi there guys, i'm a student just about to graduate university, where i've been studying archaeology, and whilst pondering what to do with my life upon leaving uni have settled on the idea of building myself a little roundhouse on some land that my parents own in Wales. I've spent a while looking at the vast number of different methods that can be used but have settled upon a primarily cob roundhouse about 15 feet in diameter with a reciframe probably turf roof. I'm pretty early on in the planning and material gathering stage but have come up with a few ideas. The soil where i will be doing the building is rich in clay so perfect for cob and i have access to a ready supply of straw and sand so cob seemed like a natural choice and is also something i've always thought is a pretty damn cool building material. I am however a complete novice to this whole thing so could do with some pointers. One of the main ones being, is it possible or more importantly sensible to rest a reciframe roof directly upon cob walls? The vast majority of the videos and other sources i've looked at consist of a reciframe on a henge wall frame, but considering the vast majoirty of this building work will be carried out by me alone (and occasionally some mates roped in from Cardiff) i wanna make this as simple as poss and a henge frame seems like quite a hassle, but any help here would be greatly appreciated. Also i'm planning on building a small mezzanine level to act as my bedroom/sleeping area but does anyone know whether a reciframe of 15 feet in diameter would provide enough height for this to be a practical possibility? I'm pretty short (about 5' 8" in height) but would still like a decent amount of room even if i'm not able to completely stand up! Also i'm kinda worried about insulation (it can get pretty cold up in the hills) so any pointers on that would be great, as would flooring. I've looked at earthen floors aswell as using some of the bricks and concrete paving slabs i've got lying around but if anyone's got any better ideas, that would again be fantastic. Sorry for the noobie post, the wall of text and the jabbering but as i say, i'm very new to this so any help anyone can give me would be very much appreciated! Cheers guys and Peace out!
Huw
 
Bryant RedHawk
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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hau Huw, Living in Wales you should be able to find a few Elders that know all about building with Cob, and they would have site specific knowledge. With luck they might be the type that want to pass along their knowledge of building Cob houses.
I seem to remember seeing quite a few when I was there in the late 60's.

Other than finding local experts, there are some really good books and websites that can be valuable sources of knowledge base.
It is my understanding that the traditional roof is Thatch and that one of these roofs can last upwards of 100 years with maintenance being low.

Good luck to you.

Redhawk
 
Daniel Ray
pollinator
Posts: 131
Location: Stevensville, Montana; Zone 4b
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Many people prefer having non load bearing walls, but having a framed cob house is definitely not necessary and usually not preferable by the single owner builder. Ianto Evans and Cob Cottage company have been demonstrating load bearing cob walls for years--definitely check them out. This is a very small house, just over 150 feet and will be perfect for a reciprocal roof on load bearing walls. Make your walls nice and thick to support the weight of your roof weight--sod weighs a lot when wet. Also remember to create buttresses to give your walls extra support.

Cob isn't going to have much in terms of insulation. If you don't have very many sunny days I would consider doing a hybrid straw bale or making your walls very thick. It won't take much to heat that small of a space though. Insulate where you can if you stick to cob walls. Add extra insulation to the roof, floor, and stem wall.

Earthen floors are awesome. I love mine, but they can be cold in the winter if you don't put insulation below them and rely only on thermal mass.

What type of foundation are you planning?

I highly recommend spending a lot of time reading through cob on Permies as well as checking out the following book resources. Try to get them from the library or buy them they will come in handy in the future:

The cob builders handbook (becky bee)
The hand sculpted house (ianto evans)
The cobbers companion (michael smith)
Earthen floors (sukita Crimmel)
The cobweb (cob cottage company)

Also, there are tons of people building cob houses for themselves and posting their results (failures and successes online) check out my blog in my signature and link to all of the other blogs/websites I have listed in my blogroll. And ask as many questions on this website as possible!
 
Tobias Ber
Posts: 493
Location: Northern Germany (Zone 8a)
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hey...

in my understanding a reciprocalframe roof would not work. the force will move downwards and sideways. so i imagine the beams would cut into the cobwalls like scissors. you would need one solid ring of wood on top of the cob walls to evenly distribute the force downwards.


for roundhouses, have you contacted tony wrench? http://www.thatroundhouse.info/

i d prefer to build a roof like that to maximaze passive solar gains :



(picture from http://www.okal.de/node/27004)

concerning that level: i depends on how big you would build your house. draw it. it s basic geometry. then you ll see if it fit s in there.

good luck and blessings
tobias

 
Christopher Steen
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Hey Huw,
A cob wall could easily be built to directly support a reciprocal frame. But in your climate and with your method of cob, you may want to consider the alternative. Six simple interior posts with six beams on top, with six reciprocal rafters on top of the beams. Or whichever number you prefer. It'll still feel round. A days work, and a drop in the bucket. 5 minutes later you could have a tarp over it all, keeping you and your tools dry. Your freshly laid cob walls are not melting away now in the rain, because that's a lot of wet clay to dry out before you lay more rows. You have easy window, door, loft, joist, shelf, cabinet, and countertop attachment points. You could still go circular around 6 posts (and I love living in my circular earthbag dome), but at your diameter, 6 straight walls is going to give you more easily usable space. Cob lends itself to a hybrid post and beam style in many ways. How did people there traditionally insulate cob? Are there loads of peat, chips or straw to mix in the cob? With a timber post and beam you mix can be less structural if you decide on a highly insulative ratio.
Also, you can probably get a reciframe pitched high enough to loft underneath, but if it's for more than just sleeping in a bad, I'd consider having your loft floor start at least a meter below your reciprocal rafters, just my opinion.
As for size, besides paper and cad, I like to draw in the dirt at full scale. People seem to grasp a space better in real size. Lay out your floor plan. Consider that well before you start. Remodels take a long time. Consider some glass doors (instead of just windows), as it'll give you opportunity for additions if the need, desire, time, money,and energy push you towards an addition.
Any neighbors have a tractor or similar, in order to bang out the walls quickly? Slip forming tractor cob off interior posts is the shit.
I reckon you'd appreciate long rafter tails so that you have good overhangs, or even a porch.
Chris
 
Tobias Ber
Posts: 493
Location: Northern Germany (Zone 8a)
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concerning that extra level... does it need to be full height like room to walk under it?

you could set it at lower height and use the space below for storage, shelves and maybe a writing desk.
 
Huw Grant
Posts: 2
Location: Abergavenny, Wales, Uk
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Damn thats alot of responses! Cheers guys thats really helpful i think i should probably explain my requirements and limitations in terms of skill and materials somewhat better though as i don't think i've been particualrly clear. First off since i have basically no prior experience in building i want to keep it as simple as possible and so if possible would like to do without anything that requires a roundwood henge frame, as that necessitates the use of joints and would be difficult to erect by one person. I've heard alot about reciframe roofs but not about much else so if theres a simpler way of building a cone roof that would more efficiently spread its weight out on the walls i'd like to hear about it! In terms of foundations my plan is to built a ditch around 1-2 feet deep and fill it with perforated pvc pipe at a shallow angle followed by gravel and on top of that build a stem wall about a foot high, should this wall be mortared with standard cement or would cob do it?.

As far as insulation goes would it be possible to create a cavity in the cob wall by leaving a small gap in the wall which could then be filled with sheep wool or some similar material. Would this work? As i could see it significantly compromising the strength and rigidity of the walls once a roof is added. The mezzanine level is basically going to be purely for sleeping on, i'll clamber up when i want to go to sleep and down when i wake up so it doesn't need to be massive. My plan was to build the supports for it into the walls for added strength and then use the area below it primarily for storage. I'm also planning to build a lot of cantilever furniture as that seems like the most effective use of space but when it comes to a floor is there an easy way of insulating an earthen floor or would just covering it in carpets, rugs and rush matting work? Final point, i've done a bit more research and a turf roof does seem to add a truely massive amount of extra weight to the roof and since its gonna be supported on load bearing cob walls i'm not sure i wanna take that risk. Is there an easy alternative or would i have to look at something more specialised likes shakes, shingles and thatch?

Tobias that handbook was particularly useful so thanks for that! i'll go and check out those books you recommended Daniel and Tobias no i havent yet contacted Tony Wrench but i know he lives pretty close to where my Grandparents have a house in Pembrokeshire so i'll definitely try to get in contact! Once again, thanks for all the help.
Huw
 
Tobias Ber
Posts: 493
Location: Northern Germany (Zone 8a)
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hey huw,

insulation: i would not want any gap in load bearing cob walls. but perhaps you could put it on the outside of the wall.
there are things you can do. wood build unto the wall that receives most of the wind will help.
a greenhouse on the sunnyside will help. you can make this from used windows or PE-foil or there is reinforced foil that people use in construction (often around scaffoldings). if you can get this free, you could build a greenhouse against half of the circumference of that house. close that in winter and shade/vent it in summer and it helps

you can build the beams of that level into the cob wall.

 
Daniel Ray
pollinator
Posts: 131
Location: Stevensville, Montana; Zone 4b
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No worries on mixing load bearing cob walls with a sod roof, just make sure that you have enough support poles in your reciprocal. Although, if I knew someone who was skilled at thatching I would have went that route, but not that many skilled thatchers to learn from in the northwest United States.

I'm not sure about the insulation within the wall with a load bearing system, I agree with the earlier reply that it probably isn't worth compromising the wall's strength as a single unbroken mass. If straw bales are not an option, consider making insulated cob with perlite and applying this to the outside of your walls. Thickening them up with a good 4-6 inches of insulated cob would help.

I would still insulate your floor as you don't want to loose heat to the ground too much. Even doing something like an "insulated cob" subfloor would make a difference.
 
Marcel Delasource
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Huw Grant wrote:Hi there guys, i'm a student just about to graduate university, where i've been studying archaeology, and whilst pondering what to do with my life upon leaving uni have settled on the idea of building myself a little roundhouse on some land that my parents own in Wales. I've spent a while looking at the vast number of different methods that can be used but have settled upon a primarily cob roundhouse about 15 feet in diameter with a reciframe probably turf roof.

i have access to a ready supply of straw and sand so cob seemed like a natural choice

A reciprocal roof on a load bearing cob structure is problematic.

Why not work with straw bale walls? Those should go up _a lot_ more quickly and insulate a lot better. Have you seen the paligloo concept? Should be easier to build solo...

http://paligloo.free.fr/
 
Christopher Steen
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A reciprocal roof on a load bearing cob structure is problematic.

Why not work with straw bale walls? Those should go up _a lot_ more quickly and insulate a lot better. Have you seen the paligloo concept? Should be easier to build solo...

http://paligloo.free.fr/



Thick earthen walls can carry huge of compressive loads. His cottage is the size of a shed but with massive walls. A little framed roof is not a structural problem here. In fact a reciframe could be argued to be the most appropriate type of framed roof for his walls, as there are no outward thrusting forces like are found on hips, yurt style conical roofs, many vaulted gables, etc. No racking the walls out of square like a simple shed roof. This reciframe will equally brace the top of his cob walls together, tying the other sides of his already super strong small circle like it was a poured bond beam.
And if he's choosing to avoid posts and beams in favor for load bearing cob, doubtful that he'd want to take on all the time and complexity of joining and cutting all those compound miters and bevels to frame an advanced geodesic and then figure out how to stuff Strawbale around it and finish out them walls (sheet the interior with all the wasteful cuts, or mask each strut and plaster around every strut...).
 
T Phillips
Posts: 40
Location: Colorado Springs, CO zone 5A / Canon City, CO zone 5B
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Hi Huw-

I only have earthbag experience, and it is limited, but these links may provide some illumination for some of your keys points.

Reciprocal frame roof on earthbag round houses - https://www.facebook.com/earthbagoklahoma/?fref=ts, and their blog - http://www.home-farm.org/september-2015/

Kevin McCabe's FB page with a recent entry about monitored moisture levels after exterior insulation was applied - https://www.facebook.com/Build-Something-Beautiful-248957378484695/?fref=nf

A simple roof bracket system invented by a Colorado engineer - http://www.ezhogan.com/

Best of luck to you in this. Hard work, yes, but perhaps the most worthwhile expenditure of your time and effort of your life. There will undoubtedly come a time when you will need others' physical help - ask for it rather than risk injury. You've only got one body to last a long time.


 
Sebastian Köln
Posts: 103
Location: Germany · Schleswig-Holstein · Eutin
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If you want to build with cob and straw, I would recommend you to take a look at the work of Tom Rijven.

He keeps doing workshops across Europe (you help building a house for a few weeks and get lectures, lunch and a place to sleep).
There is also a book "entre paille et terre ; between earth and straw", that explains how straw behaves, which mixtures work for cob and how to things work.
(One could say it covers everything needed to build a straw bale house.)

Do you need a building permit? This would probably the biggest issue for building with straw.

Insulating the floor, roof and walls with straw bales is possible.
Insulating the floor would require an air flow below the straw to avoid moisture accumulating. It also protects the foundation from small floods.
Otherwise a non-organic material (perlite, expanded clay, shredded glass, plastic bottles, anything that contains air and does not rot) would be better.

And if a hexagon (octagon, or n-gon) fits in our definition of roundhouse you could use a recipocal frame
Edit: I just figured out that rectiframe means reciprocal frame; great we had the same idea.
--
Tom Rijven - Lecture on Straw Bale House
 
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