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The Project Rises Again..advice, Please And Thanks?

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Old 08-29-2018, 12:10 PM   #1
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Question The project rises again..advice, please and thanks?

Elsewhere on the forum, there was a discussion about circular yurt walls made from strawbale. The sole problem I can see is: plastered strawbale walls won't flex like lattice. And that's what I'm planning. Have worked with several books over the last couple years; I write assuming a forum reader is unfamiliar with straw bale building, so pls forgive my pointing out some bale concepts. Also- I have very high anxiety/OCD and am a beginning builder.
I get cold easily. But can't build a "permanent" structure (zoning). And a deck won't work for me either (heat loss and pests).

Planned: a 22' diameter (if all goes really well). With ~15" thick walls of straw, a 22' diameter round has a 19'-6" inside diameter, and ~298sf, or about the floorspace of a 20' ger with a lattice. I will lose some floorspace to a cold-protective entryway. I am living in a house right now,but would love to finish before December- it's a toxic house (allergies).

So the plan: stemwall is built of courses of earthbags (stabilized soil), to keep the bale wall, min., 12" off the ground and dry. The nice thing about bales is that I can BEND them easily to form a perfectly circular wall (stomp on them in a trench). Plastered on both sides, they make a stressed-skin panel, which is very strong. Similar to a roundhouse, but the yurt roof is easier.

I found a yurt book in which the author (Lee, 2013) built them with an outer perimeter of narrow rectangular framed sections, connected, rather than a lattice. He claims that they hold up well to Manitoba winters (!) on his homestead- with 110mph winds. How cool is that.

My idea: use a similar framing system, but within the bale wall instead. Bales as infill accommodate framing well). Note- pounding rebar down through bales is now considered a poor idea: leaks= structural fail over time. The wall is ~5'-4" tall, depending on flooring.
Site is a little remote, on a slope, using hand tools only until I get a generator. Remote enough that a driver dumping off gravel would refuse, and drop it below on the lawn. So I have to haul materials up there. But- gentle south-facing slope, so it's worth it!
I'm still undecided on the floor finish- bales, and plywood? earthen?? Stress!!! Detailing and planning to beat back the swarms of carpenter ants here. GRRRR.

--> An innovation: at the top of the alternating-course, plastered bale wall, pour a ~4" thick bond beam of concrete etc., as is done with earthbags (bent horizontal rebar within, to strengthen it). This avoids having to build a super-strong wooden top plate over the bales. It should be able to resist both lateral and compressive forces in a windy place (~60 mph max). Critical: wood framing or posts within bales must then be able to support both bond beam and (fairly light) roof. I'm planning with the help of several books- Myrhman/Bergeron on straw, Hart on earthbags). But am new to carpentry.

Then build yurt roof above bond beam. Anchor all rafters to bond beam with hurricane ties or similar. The wall cover piece, fastened to the roof cover above, covers the exterior of this bale wall. I already have a cover from Groovy, and have heavy sewing machine to alter it, or make other covers.

The structure will include a complex

insulation

plan to minimize condensation (Lee's book), and create a shallow frost-protected foundation (Roy).

I will need really good ventilation also. That's why the ring-and-skylight is appealing. I'll be off-grid, so a passive system is best until I can power 12V vent fans. But I need to keep enough heat inside too.

So in short: a hybrid, proportions like a Mongolian Ger. I may do something radically different from the typical crown, though (like a commercial light tube and lots of vents). I'm trying to balance the needs of our ~4 very warm months against the ~7 cold ones (zone 5).
I remember Knecht's cool build, and the tragic mold problems which resulted when he didn't vent it very well (?)

For the first winter, those small diesel heaters look like a good bet. But I then can't crank up a stove to "cook off" mold until I install the stove or RMH. And the flue.
Questions for the (patient) crowd: opinions?
-->If anyone knows strawbale renders: What is the minimum plastering, on exterior of wall, necessary to get the insulative benefit of bales? Could I get away with just a clay slip, maybe mesh for support, if I built the 2x4 frames (covered in tarp fabric) around the perimeter, and just pushed the bales up against them? If this is possible, I may not do the cast bond beam. It wouldn't kill me to build a wooden one. But situation is a bit urgent.

-->Cold-weather dwellers (zone 5 & cooler): Having to tie an urgh (hat/cover) over the skylight isn't a deal breaker- but the acrylic

dome

sounds more convenient. Except that I've seen on here that it can freeze open in winter! Yipes! What is an appropriate skylight or other for off-grid, winter weather? Can it clear out stale moist air better than a suntube and several vents?

--> Does the strawbale wall sound feasible?

I have a Sketchup model if images would help. Thanks in advance!

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Old 08-30-2018, 07:00 AM   #2
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Default Re: The project rises again..advice, please and thanks?

TL;DR: Might someone making a yurt build a successful structure using straw bales, rather than the traditional lattice wall?
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Old 08-30-2018, 09:49 AM   #3
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Default Re: The project rises again..advice, please and thanks?

Beats me. fwiw the entire yurt roof load is carried by a tension band at the top of the wall the the rafters attach to. Good luck.
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Old 08-31-2018, 01:00 AM   #4
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Default Re: The project rises again..advice, please and thanks?

Yeah your plan sounds workable, although I suspect you might be overthinking things.
Just make sure the tension band or bond beam is appropriate to the roof you're supporting. A straw bale wall doesn't have much strength under tension!
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Old 08-31-2018, 02:50 AM   #5
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Default Re: The project rises again..advice, please and thanks?

Hey, I appreciate the feedback a lot.
This whole plan was really a cheaty way to avoid a lattice and gain some heft. No steam bending! Whoo!

Yep, Hobbit, great catch on the the massive overthink (OCD will do that).
You rock, to take actual time for this. Your candor is very useful.

And Bob- thanks. Not everyone is able to say, 'WTH? not my area', and help anyway. Am keeping that ol' shed suggestion in mind.

Bond beam, then, is key. Time for a structural-engineer review.
I may ask a building ? in future (if a forum search doesn't answer it first).

Last edited by Hey Bulldog; 08-31-2018 at 03:09 AM. Reason: just too d- long, still.
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Old 09-11-2018, 02:04 PM   #6
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Default Re: The project rises again..advice, please and thanks?

Sorry that I am late with this post, you may have already finished your project.

I don't have any hard answers, but I visited a straw bale house in Billings, Montana sometime in the early 1980's that was built by the owner sometime in the 1920's, (or maybe 1930's?), I don't remember exactly.

This house was not a post and beam with straw infill, it was stacked load-bearing straw bales with interlocking corners. I think he told me there were stakes driven between the courses of bales, (I'm not sure about that), but I am sure he said he had poured a concrete box with metal reinforcing bars around the top to support the roof, and some metal driven down into the bales and then bent into the channel and tied into the reinforcing bars, before the concrete was poured. He told me how the metal was pretty expensive then, and wasn't everywhere and cheap like the re-bar we use today, but I can't give you any details. I didn't see that part.

He had used plaster on the inside and concrete on the outside because he thought it would "breathe better". I presume he meant it could wick any

moisture

better. He did say he had to repair some cracks in the first few years of settling, and then after an earthquake in 1959. A strong shake he said, centered in Yellowstone. The earthquake cracked some of the plaster and cement "pretty good", but he said he patched the cracks and repainted, and you could hardly notice. I could see some cracks in the plaster around the windows, but nothing serious. He told me he had never had trouble with mice in the walls, which is what he said everyone who visited wanted to know.

I don't know it that helps you or not. I don't remember how I heard about him, maybe a friend of a friend. I remember stopping in town and calling him to get directions. No cell phones then.

I drove up in the yard and the old guy met me on the porch. I remember it was painted white and had some big old trees inside a fenced back yard. We walked around the outside about twilight, and then shared a cup of coffee in the kitchen. Didn't see the rest of the inside, but I wasn't invited to look, so I didn't.

I remember he said it was the house he could afford to build at the time, that he had looked at one someone else had built before him, and that his father-in-law (to be) wouldn't let him marry his daughter until he had a house and a job, and threatened his life if he tried to elope. He told me he took him seriously a the time, he was kind of rough, and worked security for the train yard, but found out later that his father-in-law was just "bluffing him". I don't remember seeing his wife, so I am guessing she had passed. He was in his late 70's or early 80's I would guess.

Spent maybe a total of an hour and 15-30 minutes there, coffee and chat included.

The house was about (guessing) 900 square feet, painted white, and had an old style hip roof, and wider than usual eves, I have often since wished I had asked or had noticed the foundation, and asked about

insulation

in the attic, but I don't asking remember anything about it. My memory after a bout of West Nile Virus with a prolonged high fever, isn't as good as it used to be, so don't remember much more about the house or conversation.

I don't know if that helps, but I don't think it hurts. Good luck on your project.


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