local sustainable bldg materials and methods?

[MarkP]

It seems like with slight modifications a ferrocement water tank would make a serviceable round hut. There is a common design for round huts in Africa. One of the more common names is a rondavel. It is essentially a one story cylinder of mud or stone at ground level with a conical roof, usually thatched. All the outward hoop stresses are taken by circular purlins so the walls see only vertical loads. There are no beams that span the diameter so it is completely open inside. I think that a cone on top of a cylinder is the ideal shape in terms of minimizing loads. With a bunch of rafters all pushing out at the base the bottom of the cone would tend towards a round shape. That being said I have a friend who had a bed and breakfast with a small spa building. It was square with a pyramidal roof. There were 4 rafters that came from each corner and met at the peak. The downwards forces on these rafters forcing outward at the top of the walls would naturally form a square and so this too was a sort of ideal shape. Once again the entire interior was open with no crosswise joists.

Modern catamarans are made of carbon fiber and are astonishingly high performance. Nevertheless the claim to fame of traditional multihulls of polynesia was that they too had astonishing performance for their time and this was because the designs made the best of the relatively weak materials available. In the same fashion properly reinforced concrete is incredibly strong but the shape of these wood and thatch cone-on-mud/stone cylinder rondavels likewise achieves exceptional strength and performance with very modest materials. As to whether these designs are strong enough for seismically active areas or whether the local building department can be convinced of such, I don't know.

I think a simple cylinder with cone roof or square with pyramid roof would be a good basis for any construction with local materials.

[Ccat]

...
Does have me thinking a bit. Me being the dome guy I am, and owning an airform, I always figured whatever I did had to be spray applied. Aircrete is generally regarded as being so fluid before setting, that the only way to make it useable was to pour into forms, making bricks of various sizes. But, I have access to some interesting thickening compounds which could made aircrete "stand up" in such a way as to be applicable to a airform. Calls for an experiment.

from what I read, plain water+concrete+foam air crete is not real strong.

Does anyone have experience with aircrete with the latex additive?  I have used the latex liquid in other mortar applications and was impressed.  Its a little expensive, however.

Ccat

[randomq]

What's done with all the "recycling"? Can't we just melt it into plastic/aluminum panels? Could be non-structural sheathing over top of local lumber post and beam joinery. The cardboard could become some kind of insulation, but I'd want it encapsulated so it doesn't get moldy.

[Ccat]

concrete block

I would have said that, but they have a tendency to get cracks in them from earthquakes and arent easy to repair or remodel.  I have a friend in Israel who has a house with this problem.  Its really expensive to fix and the fixes arent lasting that long.

Aircrete, if it was more resilient, might get past that, be cheaper and more fixable long term.  Also, would be a better insulator.  Also, theoretically,  aircrete rubble can be crushed and reused to make more aircrete.  The blocks could be knocked down for reuse.

So how do we make aircrete more resilient?  Latex, fiber, etc?

I am seriously in favor of DIY fixes for sustainability.



Ccat

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One bad thing about recycled plastic is:  Much of it will degrade in 1-3 years into tiny particles.  If it lasts longer, it may have lots of forever chemicals in it.

polyvinyl chloride, which lasts longer and is stronger, is considered hazardous waste so its not desirable either.

Ccat

[dobanion]

from what I read, plain water+concrete+foam air crete is not real strong.

Yes, given. I mentioned as much in some previous posts. The intention here, would be to build up the thickness of the shell to what I want (4" on walls and 2" overhead) with a sprayable aircrete, then immediately cover with reinforcement and followup with a~3/4" thick layer of high psi mortar to tie the reinforcement to the softer aircrete underneath.

Equally possible, substitute styrofoam concrete for the aircrete, which from at least one prominent builder on Youtube suggests is a much better choice. I still wonder where to get a truck load of waste styrofoam on the island. It is not recycled, it just gets heaped in the trash normally. I'd rather not resort to dumpster diving. What are some buisnesses you'd think would produce a shit ton of waste styrofoam on a weekly basis?

[GreenNerd]

Appliance stores that deliver. Electronics stores.

[Hotzcatz]

Years ago, someone did the math to get ohia posts a legal option for building in Hawaii. This is a tropical climate and we could grow all sorts of local hardwoods - teak, toon, mahogany, etc. If the math were done on those so they could be used for building materials, that could go a long way towards getting more sustainable building materials around here. It's expensive to have the math done by a certified engineer and submitted to the County. Otherwise all structural wood members have to be use stamped and graded woods. Kiawe posts are really durable but I think that's a slow growing timber.

There used to be canec, which was really sustainable - as long as there were sugar plantations. Canec was cane bagasse mixed with arsenic, made into flattened sheets and dried. Great ceiling material as long as it stayed dry and nobody nibbled on it.

For non-structural wood, there's a lumber company up in Waimea which gets fallen trees and cuts them up into slabs and such. Locally sourced, not exactly inexpensive, though.

If you want to build a Hawaiian hale, they are in the code book so they can be built as a legal structure. Not sure if they can be a legal dwelling, though.

If you want sustainable and inexpensive, how about weaving waiwi sprouts together to make growing walls and suspend a Sunbrella roof in it? The water off the 'roof' would water the waiwi roots so the walls could grow faster. Might make a nice pavilion out in the yard, dunno as if you'd wanna live in it, though.