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roof for cob construction
friends i want idea for constructing a roof above cob wall structure. for the project i am going to use circular forms mainly, thaching is first solution... but i need to know about how it should be done? what are the critical issues i need to address?
Zakiyah Patel
Responses
 
roof for cob construction
hi zaara,
yes thatching is one good option about cob walls. you can also use country tyle roof above circular forms.
the critical thing about the roof above cob wall is you have to provide enough overhangs in all the sides in order to protect the mud walls from rain.
you can project thatch better than the country tyles. if your building is in low rainfall area you can use country tyles or its in high than you can use thatch.
Charmy Sony
roof for cob construction
can you pls tell me the location of your structure, like in which region do you belong?? i am going do a similar effort in the Saurastra region of Gujarat.
Charmy Sony
roof for cob construction
Dear Zaara and Sony,
If the walls are thick enough you can also use RCC roof with projections enough to protect the wall from rain water sliding down which is a critical need to be addressed.
Sony, We have used Rcc as well as tiled roof on Cob walls in a resort in Madhya Pradesh near Itarsi.Few rooms with flat roof were done so that one can use the terrace for sleeping in summer nights.
Chitra Vishwanath
roof for cob construction
Once again watch our cob set from BIOME.Some pictures are of a Ground +1 house under construction in Bangalore.http://www.flickr.com/photos/biome/sets/72157611479219681/show/
Regards,
Chitra Vishwanath
roof for cob construction
hello mem,
thank you for your responce.
I refered your weblink.
I saw the images, I am confused about weather the walls are of cob or sundried bricks ?!!
In case of g+1 building, how do you protect the ground floor walls from rain water. do you apply any additional material in plastering ???
I want specific details for thatch roof over curvilinear forms.
if you can provide me some images with details.
thank you mam.
zaara
Zakiyah Patel
roof for cob construction
Dear Zaara,
Thanks for writing back.The structure which is G+1 has been constructed in Bangalore. The cob walls are 15" thick and they have 5% cemnt stabilization. They are not mud bricks. The 12" projection in the last slab will protect the building from the erosion affect of water running on the surface of the wall. The extent of roof projection depends upon the rainfall occuring in the area.
Chitra Vishwanath
roof for cob construction
Zaara, Cob walling was used with frame structures and is probably a variant of "wattle and daub". Therefore your roof can be supported by the frame or posts and not by the cob wall itself.

As for having enough of an overhang to avoid degrading the cob wall by rain, you should be aware splashback from the ground eats away at the cob walls, so it is helpful to have a solid stone or fired brick base (above the ground) on which to build the cob walling.

In passing, cob walling is similar to "rammed earth walling", the only difference being that cob walls are built up of rectangular rammed lumps of clay, whereas, rammed earth is layered within moveable shuttering.
Frank John Snelling
roof for cob construction
A framed roof structure will do,
Mwalyo Ndulu
roof for cob construction
As the British adage goes for any building provide a big hat and high shoes and the same is protected for centuries..
Agreed, John an important aspect is high plinth which should be ideally made with any local material which would not wash away with water and also to have overhangs which go much beyond the walls in high rainfall areas.
Zaara, it would be good if you let us know as to where( geographically) are you planning the building? Otherwise we would be giving ideas non contextually which may be very confusing to other readers .
John, cob, as I know is not a variant of wattle and daub and can take roof loads and does not need framed structure below. See one of my posts earlier wheer we have built ground floor and also ground+one floor using cob and flat roofs of RCC.
More discussions welcome since we at Biome feel cob is a very good way of construction since it avoids burning fossil fuel of any kind, provides employement to many including women, and does not require machinery or frames for construction.
Regards
Chitra Vishwanath
roof for cob construction
thanks friends.....
now the site is situated in jamnagar,gujrat, india. i agree to raise the plinth to a sufficient height, local stones will do that. john i also belive that a cobwall can resist load comimg from top. walls will do itself.
now one issue is... how much is it efficient to buit linear wall with cob?
Zakiyah Patel
roof for cob construction
Chitra, I was being plastic with meaning when I said cob was a variant of wattle and daub because I was thinking of the characteristics of materials used.

By this I mean that "wattle and daub" uses fibrous material (such as wooden stakes and rushes) mixed with clay or dung and similarly "cob lumps" can be made of clay and straw, rushes, etc.

In passing I forgot to mention the other materials similar to cob which is the lumps of earth and living grass cut from the ground and known as "sod" or "turf". For instance the Vikings used to build low turf walls and put their boats or ships upside down on the walls for winter quarters.
Frank John Snelling
roof for cob construction
hi zaara.
you know any of the architects in ahmedabad gujarat
who works with mud? i would like to work on such projects after my thesis. please do let me know.
Meehaj Thakkar
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