approach will also be successful for long term low cost resilient housing and infrastructure. Ferro-cement sandwich panels seem like a very reasonable place to start this effort for several reasons; high rigidity, durable water proof surface, excellent thermal properties (depending on sandwich material and thickness chosen), and because of the strengthening effects of wire mesh this all occurs with minimized cement costs.
Basic Construction Approach
The ferro cement sandwich hexayurt will be built in a manner very similar to the current hexayurt designs with the addition of ferro-cementing procedure. For the intended 12' hexayurt model this means building the initial structure out of 18- 4'x8' EPS boards or cellulose filled hexacomb boards, depending on site availability and economics, the later would be a very low cost method. To fasten the pieces together wire, or foam staples will be used to pin joints in place, as the shell only needs to be held together until wire mesh and ferro cement are applied.
Windows and Door
At this time the desired window and door arrangement should also be cut from EPS or cellulose board.
The cutout window sections will then be hollowed out with a 2� perimeter to make for a ferro cement frame coated clear poly film window. The same process can be repeated for summer screens. The door panel cutout section must be trimmed to accommodate ferro-cement layers. This can be done after the shell ferro cement application is complete. The door then is ferro cemented with hinges in place.
With the smaller 12' hexayurt space is at a premium so it is unclear at present how best to divide the structure to give privacy to family members. Adding a divider wall, or maybe just a divider curtain could be done at any time though once optimal layout was determined.
Foundation and Floor
The shell is next ready to go on top of the foundation. Here flood patterns, earthquake, and frost tendencies must be taken into account.
An initial generalized approach that should cover many of these concerns is to build a 20' diameter gravel mound (or other available fill) to the needed height above ground line. This mound, or at least the pad the hexayurt sits on top of can be ferro cemented over to form the floor. A central drain pipe that exits at the base of the building pad can be added to drain sink grey water (15' 1/2� PVC pipe). If it is desired to isolate the yurt from the ground heat sink (cold climates) then additional EPS boards or cellulose wafer boards could be added before the foundation is ferro cemented over. The hexayurt itself will sit on top of a raised 3-5� high, 1' wide ring of gravel. This may be done with or without forming of some kind, so long as it is smoothly meshed with ferro cement
This approach would mitigate flood damage, and also isolate from ground heaving in the event of an earthquake or ground frost heaving.
Future Foundation Techs Cistern/Cool Ground Heat Sink
Future considerations for the foundation would include burying a ferro cement cistern beneath the foundation for rainwater capture. The cistern would not only be a filterable water source, but also provide ready access to the ground heat sink for hexayurt cooling needs. This could be done with a fan and vent pipe, but is beyond the immediate scope of this project.
The next step is to encase the entire shell in a layers of wire mesh on both the inside and outside of the shell. To make the shell a bit stronger, at a marginal expense to insulation quality, every couple of feet a wire can be pushed through the shell and used to tie the inner and outer wire mesh layers together. Readily available chicken wire is reported to work well for this and be of low cost.
Ferro cement Application
Typical ferro cement mixtures require 1 part mortar, 1 part sand, and It can be mixed and troweled on by hand, or the cost of an electric mixer, air compressor, and mortar application could be spread over the cost of a village project.
There will be an ecosystem of low cost, locally build able infrastructure options that will evolve with the project over time to suit the diverse needs of regional communities, climates, and economies. The immediate basics that will be used in this model are.
-Central DIY Gasifier rocket stove~$15
-Low cost PV LED lighting system such as http://illuminationhq.com/
-Sulabh two pit style style toilet system (ferrocement lined) http://www.sulabhinternational.org/st/advantages_sulabh_toilets.php
-Solar oven, DIY tube variety ~$10
-Ferro cement cast biosand water filter ~$10-15
-Ferro cement cast sink and frame ~$5-10
-Locally preferable furniture and housing textiles, if no preferable materials exist ferro cement process can be used to make furniture and other needed fixtures.
-Solar trombe wall, could be as simple as tar paper on southern exposure for winter time heat gain.
-Passive solar modules for yet colder climates (use best DIY practice from web). If large amounts of passive solar are required the whole souther part of the building berm can become a passive solar panel.
-Heated floor, this could be as simple as digging channels beneath the ferro cement floor that will act as air ducts to circulate hot air gathered from the passive solar system.
-Alternative building sizes and room configurations. There already exist several hexayurt building floor plans for a variety of spacing needs, and can provide for families of different sizes and different needs.
BOM for Minimal Ferrocement Hexayurt
18-4'x8� ESP panels $180, ~$60-80 for hexacomb cellulose stuffed boards.
Chicken wire 1� mesh 20 gauge, 2- 4'x150' sections $136, Enough extra for sink, toilet, and other furniture builds.
Wire rolls for attaching mesh and joints ~$5
Ferro cement mix (assuming 3:1 sand to mortar mix with sand cost excluded). Needed volume @ 1� cover for total shell~48ft^3, need 1/3 that or 16ft^3 as cement @$3.33/ft^3, Total cost~$53 but round up to $75 (enough extra for toilet, sink and other castings)
Solar LED aa rechargeable lighting system ~$20
Sulabh Style Toilet: Costs are covered in ferrocement materials (cost of mold spread throughout village) http://www.sulabhinternational.org/st/advantagessulabhtoilets.php
Solar Oven DIY Funnel Type: ~$10
Rocket stove: DIY ~$15
Ferrocement cast water filter:~$5 for PVC piping and fittings (cost of mold to be spread thorughout village)
Misc: PVC pipes (sink drain), clear poly film, screen (windows) ~ $10
Sink: Costs are covered in ferrocement materials (cost of mold to be spread throughout village)
Gravel or fill: NA as gravel or suitable fill hopefully is available nearby for cost of labor to move.
If cellulose hexacomb panels are used, it is possible to have a fairly well equipped durable, livable home with key infrastructures for ~$340. A little over but very possible, right now.
More importantly the open source approach to this should project should encourage collaboration and further evolution of low cost local build techniques that will both drive down these prices, while also building up these local economies and hopefully bringing them into the emerging online marketplace.