How can I cover a reciframe roof in rural southern Mexico?

Hey everyone,
I'm new to the forums. I am a teacher of permaculture at an orphanage in Mexico. We are working to transform the whole of our Ashram here into a much more ecologically suitable situation. Here they use concrete for EVERYTHING because wood is very difficult to come by and very expensive. There is no sustainable forestry anywhere around and most agriculture here is slash and burn and quickly being coopted by the agro industry giants that are slowly being urged out of the more "developed" countries. Anyway, we are building a model home now that is a 5 meter diameter roundhouse. It will be a hybrid of earthbag and wattle and daub with a reciframe roof. Most materials are easy to come. We have ample access to clay soil and there are many yards full of bamboo in town that are happy to have them trimmed up and the old culms removed.
I am running into issues with the reciframe roof. I have the timbers I need but I am concerned about ra roofing option. Green roofs irk me due to the dependency on synthetic materials for the membrane and padding etc. Even if I was fine with that, we cannot access those kinds of materials here in this part of Mexico. My side question is how can green roofs be viable for people in these areas without increasing industrial pressence in those areas to produce a "green" industry. Anyway, the third obstacle is that we only have 4 months of rain here and the rest of the year is drought. This would mean that the roof would likely need to be watered and water is a precious commodity here given that we collect our rain in the rainy season for the whole rest of the year.
I am exploring other options but I wanted to see what the experienced builders here had to say.
What can I cover the reciframe roof with that would be sustainable (ecologically and economically) and if a green roof is an option are there any experiences of substitutes for EPDM and the other materials that are just as effective and may be available here.
I should add that even though I am a permaculture teacher here it doesn't mean I am incredibly learned in green building. I mostly specialize in growing and I have experience with building and especially with cob but framing, roofing, etc. is a blindspot as most of that knowledge is still from my days in conventional construction. It would probably be better if a permaculture teacher knew more about green building but its hard to find experts who don't mind living in rural Mexico and working 12 hours a day for no pay lol.
Any advice is greatly appreciated.

How about a traditional palapa roof?

Hello Datura, et al,

I will try to assist you where I am able. I must second John E's post...Palapa Roofs, Chickee Roofs, and several other vernacular are more germane than than trying to emulate one of the "new reinventions" of traditional methods. As I am know for saying...look to the vernacular building systems of a region, and start from there.

I believe the proper term you are looking for in the roof framing system you are considering is reciprocal roof and this may be applicable, or not.

As for a "living roof"...well...I typically find them "faddish" if not being done in a traditional way...on architectural forms that are...again...traditionally know for them. Yes the modern ones look "cool" yet do indeed rely heavily on very expensive modern materials and industrial methods. If you have a vernacular style of living roof down there...(I don't believe you do typically) then use that style...otherwise, I would not recommend them to you.

Hope that helps a little and gets you thinking in a good direction.

Regards,

j

Thanks John and Jay,
Palapa or any kind of thatch roof is not as viable here as you might think. We are high in the volcanic mountains and there are no palm trees here. The forest is much like you would see in the Georgia mountains. I can try to get fronds brought in from the valley about an hour away but that could be costly given our location. Its very difficult to find vernacular building systems as this part of Mexico and most other parts as well have been so de-culturalzed and now even the old timers are swearing by concrete and rebar for everything. In any research its also hard to pinpoint the native ways because the climate, terrain, and vegetations changes drastically within just a few miles. I will continue to look into the native methods and keep you posted. Thanks for taking the time to reply.

Also, with a thatched roof I am thinking that the pitch will need to be much greater than what a reciframe typically offers. Although with using grass or palms I wouldn't need to carry as much weight and so the reciframe may be overkill anyway?

Hi Datura, et al,

Do keep us in touch.

If you are not in a palm or thatch roof area, then they probably used a shake or slate for roofing. If you give me your exact geographic local, I can be of more service. Reciprocal roofs are neat looking and do have merit yet are not really a vernacular form in most arias. Also, "round" architecture (especially vernacular forms) are almost always of a "transient nature" and not meant for permanent installation. (ie yurt, ger, ti-pi, igloo, etc.) Most are still either square, or rectangle with gambles while some are octagon with corbel roofs like you would find in parts of Mexico and on the Dine' reservation. I look forward to being of more service if I can.

Regards,

j

you write, you have bamboo at hand.
Is it possible to use this either split and flattened in form of a mat, or split in halve and used as a type of shingle? Sorry, my language skill in english reaches its limit when trying to translate 'mönch und nonne'. So I embed an image of german wikipedia to explain what I mean.



You probably need some more bamboo to create some support for those shingles first.

Thank You Ludger,
I've contemplated this idea but would the bamboo not decompose or become infested with insects? I don't have any way that I know of to treat the bamboo that I have access to. Thank you for the suggestion. I've often wondered if i could implement the same idea with recycled irrigation tubing.

Jay C. White Cloud wrote:Hi Datura, et al,

Do keep us in touch.

If you are not in a palm or thatch roof area, then they probably used a shake or slate for roofing. If you give me your exact geographic local, I can be of more service. Reciprocal roofs are neat looking and do have merit yet are not really a vernacular form in most arias. Also, "round" architecture (especially vernacular forms) are almost always of a "transient nature" and not meant for permanent installation. (ie yurt, ger, ti-pi, igloo, etc.) Most are still either square, or rectangle with gambles while some are octagon with corbel roofs like you would find in parts of Mexico and on the Dine' reservation. I look forward to being of more service if I can.

Regards,

j

Thanks again for the great advice Jay. From my research it seems that those without access to palms made use of reed and grass for straw thatch. I'm going to see what I can find in that area. In terms of shape of the structure, I built a 1.5 meter high stemwall with our local volcanic rock and the shape is round, however there is a skeleton of timber. I have a henge of 13 verticals and I am using 13 timber rafters. The actual shape because of the henge is going to be a 13 sided polygon. I am going to carefully consider your advice as I sense we share a passion for natural and native living and also perhaps a shared skepticism of the modern "green" ideology.

Great advice Ludger...yet the reason I did not suggest just that was the fact that as nice as bamboo is, and such a wonderful building material...the hidden dragon in the room that few natural builders are discussing (or often aware of) is the fact that there are fungus and insect pest that can render it useless in just a season or two. I am involved in several "design build" programs in the tropics as a consultant and the issue I am having with bamboo (still really trying to figure out alternatives) is they must be treated with harsh chemicals/pesticides if you want them to last any length of time. Borates are showing promise and are one of the less harsh chemicals.

So, again, great idea, yet not enduring at all. Clay tile and slate is a strong option if Datura can find or make them.

http://velacreations.com/shelter/building-components/roof/172-latex-concrete-roof.html


Abe Connelly used the low resource roofing system above, in a enviroment that seems like it is similar to your own.

So, again, great idea, yet not enduring at all.

Well not so great after all. Glad there is somebody here with actual experience in the tropics.

Its hard to guess what type of treatment would make bamboo more durable. I assume you tested traditional chinese or japanese methods like smoking, charring and drying and they failed in the tropics?

Ludger wrote: I assume you tested traditional chinese or japanese methods like smoking, charring and drying and they failed in the tropics?

Yep, as I specialise in Middle Eastern and Asian vernacular folk styles of earth, stone and timber. Bamboo is great stuff, and many new age "natural builders" are crazy about it...many however, are pushing it well beyond its typical application of "transient and sacrificial" use and application. In places like Thailand, and related locations, they soak the poles in tanks of really "ICKY" chemicals to give them longer life spans...not very sustainable or environmentally applicable...from my perspective. Still a lot of research and re-thinking on this one. Some regions the bamboo can last longer, in others...not so much.

Regards,

j

Take a look at the roof section of this water tank: http://velacreations.com/water/water-storage/item/313-cistern-howto.html



It's 3 layers: PVC structure, billboard tarp, mesh/latex concrete

The PVC structure can be wood, staple the tarp and mesh to the wood. The tarp can be any vapor barrier, but heavy duty is better. The mesh can be orchard netting or shade cloth.

Alternatively, you can do a ferrocement roof, which is similar but uses metal reinforcement, no latex/acrylic, and is thicker: http://velacreations.com/shelter/building-materials/concrete/144-ferrocement.html

For tropical areas, it's better to have a steep roof, not only to creating a rising heat draft, but to reduce chances of water infiltration.