[GSBN] natural building in haiti, pt 3

[ejgeorge at riseup.net]

and some more responses - I've condensed or summarized some to keep it shorter!

Response from Marc R.

I'm not knowledgeable about SB and plasters. What Robert has written, however, is what I 
would say as well. Interior and exterior air conditions are the same because the 
buildings are open, so there won't be a significant drive for vapor diffusion - except 
when the walls are wetted on the exterior and the sun hits them, in which case the drive 
is strongly inward and argues, as he has, for a vapor open interior finish.

I've never been to Haiti. My best friend lives in St Croix. Houses there are masonry with 
large overhangs (often called porches). It takes a lot to make overhangs that can 
withstand hurricane winds - steel clips help. I'd be tempted to design "breakway" 
overhangs that go away in a hurricane while leaving the roof in place if I couldn't 
guarantee that the overhangs were strong enough. Also, I think the masonry is a good 
choice because of insects and vermin.
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from Dave L
I'm glad Mark P. raised the issue of traditional building in Haiti. Traditional building in this case as in palm wood, isn't even available because Haiti is almost devoid of trees, they've been cut for firewood. That wood was probably used for houses because it was quick and easy to build with, not because it was the most durable. We can fight nature by trying to become permanent, or flow with it and rebuild quickly, this largely depends on the resources available. Light wood frames, if available, may blow away, but aren't nearly as dangerous as earth or poorly reinforced masonry in the case of an earthquake.
Strawbale has the ability to absorb seismic energy and if put together right can stand up to high winds, but is very vulnerable to moisture. The danger from moisture in a hurricane prone area is not from the sun driving moisture into a wall(that is way overstated), its from wind driven rain. In a hurricane the smallest crack in a wall can let massive amounts of water into a building. I know someone who's entire apartment was destroyed by water in Florida because a window was left cracked open, just imagine bales(ugh!). The pressure and moisture of a hurricane dwarfs the pressure and moisuture of a heated home in winter in intensity. So, if bales are used in Haiti, the plaster should be deigned durability first. An exterior wall in Haiti should stop water/rain. Would it need to stop water vapor? From all I've heard there is a difference, and blocking water doesn't necessitate blocking vapor
 Under average conditions it sounds like there is no pressure differential in the average Haitian home. As long as the surfaces can dry and moisture isn't driven deep into a bale there should be no problem man.  Does anyone know if grains are grown in Haiti or the Dominican Republic, is straw available? If it is we at least know Andy can get bales, and that the weather conditions allow for appropriate drying.
I too applaud your efforts Andy, this can and will be done. 
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from Kevin C

If it is anything like Costa Rica, the inside air pressure is the same as the outside (no 
windows), so only thermal drivers would matter.  In spite of the stack issue, I think a 
rain screen wall might be necessary to make the water barrier on the exterior.  
Horizontal rain is rough.  I can imagine a lapped wood wall taking the energy from the 
rain, but still letting water through to a clay layer - then readily evaporating on the 
exterior thru the vented space.

Bamboo might be good for roof and wall framing, in which case all thread rods and 
washers/nuts with simple lapped connections work well.  The cores at the connections 
should be drilled and grouted after for stiffness.
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from Ben F
Is straw an available material in Haiti? Grain residues are not usually easy to come by, 
nor should they be, in tropical and sub tropical locations. I would question the use of 
massive wall assemblies in such a location. Bamboos - dozens of species to grow housing 
with and quickly - inside of 3-5 years. 

Without deforestation and land-use context, the discussion appropriate building materials 
in Haiti is missing a huge piece. Agroforestry cropping system where diverse building 
materials - heavy on bamboo and thatch - are a huge part of rebuilding both forest and 
infrastructure in a place like Haiti. They both can lend seismic resistant, light, 
comfortable buildings that 'give' in hurricanes and are quickly repairable.  Both can be 
used with termite resistance, though this is tricky.  Masonry is the other big option - 
but of course has many compromises ecologically, economically, and seismic wise. 
Depending on grain and other annual crops for building materials makes no sense 
ecologically in monsoonal climates like Haiti - no open-soil tillage-based agricultures 
have been viable in such regions.  Tree crops can be, however. 

Or earthbags...Nadir Khahlili I think (spelling?) has done tons of work on this with particular respect to seismic resilience.  They broke the testing truck on southern CA when they tested his domes for earthquake resilience.  All you need is fill, mostly, for earthbags.
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from beng

I think precompressed earth block could be a interesting possibility as
well. 

I would suggest some kind of light right screen to keep the rain out rather
than a more impermeable surface.  Perhaps even something that could hang
from the eaves, reed mats?  Reducing the potential drying to the outside
from wind or sun seems like going in the wrong direction.
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from Derek 
I'm worried about all of the materials mentioned as candidates for rebuilding Haiti.  
Compressed earth block combines three bad earthquake attributes: heavy, weak, and 
brittle. The same is true for adobe, rammed earth, and cob (although they aren't 
identical in all earthquake resisting respects).  Bamboo is like candy for insects, 
microbes, and fungi.  Untreated, it will decompose very quickly. Treating it with borax 
or other chemicals can make a big difference, but it must be done right, within a narrow 
time window.  Even then, the lashings or other connections are points ripe for failure. 
Strawbale has the moisture concerns that we have been discussing.

Bruce King described Nader Khalili's earthquake tests on earthbag structures in terms 
that wouldn't pass FCC regulations.  Doni Kiffmeyer and Kaki Hunter are great builders 
and good friends, but not earthquake experts.  In their presentations that I have seen, 
they have relied on Nader's assertions.

All new ideas face a popular acceptance question and doubtful maintenance.  This is a 
really hard problem.  I think it makes sense to try a number of things, and to recognize 
that adequate housing won't be solved overnight.  The new ASTM(?) guidelines for earth 
building with greater earthquake safety have been out for just a few months, and I 
haven't seen them yet.  They likely have useful information for us to consider.
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