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Connecting Superadobe vs Rectangle

 
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Hypothetical. Say I want to build a 30' long house with a depth of... say18'. Would I do connecting Superadobe or some sort of reinforced rectangle? I'm in dry cold desert with clay and about 2' frostline. I don't want a basement. I have scoria close by and I would insulation with a second wall or use it in primary wall. No second floor. My main interest is longer building will get more sunlight to back of building. I would like to back fill north side if it makes sense for the building. Thanks.
 
pollinator
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Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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Instead of having L shape corners just make + shape corners. You get the usual L corner for inside the building and for outside the corner you have the a tapered supporting wall.
 
Brad Horner
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Yes, I have seen that. Thanks. I feel good about the rectangle but I wanted to see if someone would talk me out of it
 
S Bengi
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rounded corners are good too but then the roof beam.
 
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Location: Colorado
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Rectangle?

A wrecked angle?

Don't ruin the angle!

How about the try angle :D

Seriously though - you've got clay and scoria, make it an ellipse, a star, a something-o-gon... just make it! You already have most of what you need, but you know that...

The south wall 30 ft with a bermed north wall would be ideal - just use the earthship secret: take your solar elevation and plot your windows so they are perpendicular to the winter solstice, with shading for the summer solstice. This causes direct sunlight in the coldest part of the year, and no direct sunlight during the hottest part.

Dirt hut! Yay!

Though - circles are inherently stronger, and domes are longer-lasting without the need for a separate roofing structure. Rectangles are good though! Technically, it's a rectangular prism unless you live in flat-land.

Oh! Don't forget to buttress! Seriously - DON'T GO WITHOUT THEM! Every 4 ft or so, and make sure that your trusses or rafters land on them (not all unless you do 4' centers)
 
Brad Horner
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Spencer Miles wrote:

Though - circles are inherently stronger, and domes are longer-lasting without the need for a separate roofing structure. Rectangles are good though! Technically, it's a rectangular prism unless you live in flat-land.

Oh! Don't forget to buttress! Seriously - DON'T GO WITHOUT THEM! Every 4 ft or so, and make sure that your trusses or rafters land on them (not all unless you do 4' centers)



Ok I just added this to mah plan. Thanks!

Roof is main question remaiing. I could try and harvest vigas from Carson National Forrest:
Green Vigas (all species) Dead Vigas (except dead, standing Ponderosa Pine)

6.9" DBH & Less - $0.05/LF
7.0" DBH to 8.9" - $0.15/LF
9.0” DBH to 11.9” - $0.20/LF
12.0” DBH to 15.9” - $0.50/LF
16.0” DBH to 19.9” - $0.70/LF
20.0” DBH to 23.9” - $0.90/LF
Designated areas only for green vigas

I'm also interested in nature cement roofs like a ceramicrete thing. I feel lacking in knowledge with that.
 
Spencer Miles
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Brad Horner wrote:

Ok I just added this to mah plan. Thanks!

Roof is main question remaiing. I could try and harvest vigas from Carson National Forrest:
Green Vigas (all species) Dead Vigas (except dead, standing Ponderosa Pine)

6.9" DBH & Less - $0.05/LF
7.0" DBH to 8.9" - $0.15/LF
9.0” DBH to 11.9” - $0.20/LF
12.0” DBH to 15.9” - $0.50/LF
16.0” DBH to 19.9” - $0.70/LF
20.0” DBH to 23.9” - $0.90/LF
Designated areas only for green vigas

I'm also interested in nature cement roofs like a ceramicrete thing. I feel lacking in knowledge with that.



Ok, so here is vaahht-chah-dew... (I've included pics because this might get convoluted.)

The difference in height between your north wall and your south wall will be side A, the width (including wall thicknesses) of the place on the north south line is side B
Pythagorize to get C - this is the length of your rafters, and the angle from B to C is your roof-pitch (it's very tangential....)
Of course, you could have your south wall higher than the north wall, but that will shade the roof and cause an ice-dam. Either way, the math is the same.

Cut your logs to length C + whatever eves you do. If you do nasty-thick framing for your roof, 48" centers are fine for the rafters.
The North wall is bermed, so buttresses are not needed, but during building you'll need to keep in mind that your rafters will push on each wall by the sine of the angle (30 degree slope pushes outward as much as down - this is a big deal!) so berm as you go. Thick walls and a low-angle roof make this not matter much.

Strip, hew, or otherwise treat your rafter logs to make them pretty to taste - as long as they're sound and thick, it really doesn't matter. I have a table of spans indexed to lumber dimension if you need me to look up the maximum span (width of your house)

Personally, in this set-up, I would go with a shallow roof pitch (a 3:12 is around 14 degrees, so a 1000 pound roof only pushes out 241ish pounds). Running with that example, your rafter logs would be 12.36931688 feet - plus the eves.
The eves are the hypotenuse of another triangle figured from your summer-solstice sun-elevation - see diagram of the shadow you want.

Add a vent at the highest part - this lets the hot air go out, and suck cool air into your open windows (or a corrugated tube running through the earth berm) - it's convection man! Obviously, you close the vent in the winter.

Before covering it, if you're fast and the weather is good, you can lay your ceiling like a floor on the rafters - T&G or that fake wood-floor stuff (good side down) - then cover it with 6 mil polypropylene plastic, then do the roof cover. This is SO MUCH easier than over-head work, but it is weather dependent (if it rains on your ceiling, it's ruined...)

Now you have a framed triangle on top of your rectangle. How do you cover it?

You could use 2x4 16"OC, or 2x6 24"OC (standing... obviously) as they only have a 48" span. Then cover it with OSB or Ply, then roof as normal (steel good, asphalt bad, soldered copper is the holy-grail...) Insulate to taste - R30 is great, but we live in the real world.

OR!!

You might check out the DIY Concrete Cloth thread on Permies, or just Google "Hypar Roof" - in this instance you'd "frame" between the rafters with 5 - 6 feet of PVC with Rebar inside it, squeeze it between the rafters and it'll automatically make an inverted catenary (pretty much the strongest shape in the universe) - just be sure that the PVC is 90 degrees from the rafter, and the ends are in line with each other.
Take some Polypropylene mesh (DO NOT use Polyethylene, it stretches!) and brush Portland cement slurry (with acrylic goo) into the mesh. You need to use open weave (like silt fence) so the cement can get in there.
Then layer up on top of it more cement - change the mix as you go, adding polypropylene chopped fibers and scoria (I hear you've got some of that).

If you do 3 - 6" of the scoria (or pumice, or styrofoam beans, or furnace cenospheres) stuff, you won't have to have a separate insulation layer - it's all about the trapped air brother!

Finish the last inch or two with some good acrylic-fortified cement or lime stucco. You'd be surprised how cheap this method can be, especially compared to wood and asphalt - and it'll last pretty much forever.

For your peace of mind, add in a 6 mil layer of polyethylene plastic for water-proofing/vapor barrier. 40 mil ETFE would be the absolute best for that - after hypar and scoria-concrete, but before the stucco layer. That ETFE can be got surplus or reuse (craigslist, ebay...) It's basically pond-liner used on flat commercial roofs.

Underside (ceiling) of the Hypar can be done with skip-trowel drywall mud. If you do a smooth layer of All Purpose Mud, paint it light blue, then do a skip-trowel texture and re-paint with white (use a VERY thin roller) then only the texture blobs get painted white, and the ceiling looks like a blue sky with puffy clouds! Hide some cheap Amazon LED strips in the rafters (where they meet the ceiling) and you get a super mood-light effect. Run the LEDs on your solar setup...

Finally, should the roof end up being 4-6" thick of the hypar stuff, you can put some sod on it. A grassy-hobbit-house-roof-thing...

I do feel compelled to tell you that I am in no way responsible for how someone uses my suggestions... haven't got any money to sue away in any case. These are suggestions. Based on lots of research, but suggestions none-the-less. Caveat Emptor!

Anywho - the magic is in the triangle and the catenary. Even though your house is a wrecked angle, the magic is in the triangle! Even the buttresses that I mentioned are triangles... Triangles and Catenaries are AWESOME!!

SO! I am happy for you!

If any of this is useful to you, consider some love for my plug (but feel no obligations... seriously, I just like helping, but could also use help!): Crowdfund Thing


Here are the "diagrams" that I penciled in for your thought-food. Would love to see your project.



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Spencer Miles
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BLAH!

It's "Latex Concrete" not Hypar - a Hypar is a shape, the Latex concrete is the material....

Confer: Latex Concrete

Sorry....
 
Brad Horner
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I'm I'm process of absorbing this info. I'll reply some time when I properly get a grip on this. I like what I'm learning though. So cool, ty. I will be hoping the latexcrete can be done. Sounds amazing. About to check into it.

Edit: I like it. The sandwiced scoria is pretty light weight I think. My problem of the moment is rain catchment with an inverted cantenary.
 
Spencer Miles
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Cool brother, makes me super happy to be of service - elsewise I just know a bunch of crap for no reason (that's called being a prick) :(

Keep in mind with the Latex Concrete that its first and major purpose is to define the shape - it is certainly strong enough to be a roof on its own right, and this is what most people do with it but, it functions as a sort of permanent form to pour ultra-lightweight crete (portland, PP fibers instead of sand, and Scoria or Pumice instead of gravel - all the same proportions a "Quickcrete" just replace as mentioned). The thicker you make it, the stronger it gets - but don't pour more at a time than the previous layers can support!

It might make you happy to know that this sort of Composite-Composition (PUN!) is what is done in nature - a thin, super solid shell filled with foamy, lightweight material. This is what makes bone, bamboo, and beak stronger than steel (or concrete) - even though bone and beak are nothing but chalk with some phosphorous, and bamboo is little different from paper.

The plus side is in the insulation value - all that air in the pumice or scoria (or, again, cenospheres or styro-beans, or even shaving-cream-made-of-better-soap) makes it both lightweight (some versions float) and gives it an R-value between 2 and 4 per inch - that's the same as that super-expensive foam sheet, and a gazillion times stronger!!

Also, please don't let my descriptions give you the impression that it's super complicated or anything - it really isn't at all, it just seems that way when it's all written out. If you can lift a shovel, you can do this.

I'm so excited for you!! :D
 
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"keep in mind that your rafters will push on each wall by the sine of the angle (30 degree slope pushes outward as much as down - this is a big deal!)"

This is true for a gabled roof if the ridge is not independently supported or trussed, but a shed roof, no matter how steep, will only push down. (I suppose wind load on a steep shed roof could be a factor, but will probably be negligible compared to other factors.)
 
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