I realize that plans such as this are not a literal final product, and technicalities and details get worked out along the way by the common sense of the builders. But I have a few questions that come to mind based on the drawings.
1. Will the roof be covered in dirt? If so, how will you keep it up there and still allow water drainage? I ask because it seems typically that an earth roof runs into the earth berm and you have an uninterrupted "dirt flow" that holds itself in place and lets water flow through the soil naturally. This design appears to have the roof elevated from the ground all the way around.
2. Will you backfill dirt against the sides and down-hill side? If so, what are you planning to use for siding/shoring material? I've never heard Mike admit or even acknowledge it, but his "approved design" of using 2x6 tongue and groove siding *always* fails, even on spans as small as 4 feet, and even with a soil depth as low as 3 feet. Thin walls like that always bulge in. Bulging means there was movement. Movement creates a high risk of perforating the waterproofing material. And bulging walls are ugly, and a bit scary. This design here shows 10 foot spans. The pictures of the actual site don't indicate much of an excavation, so maybe the sides won't be very deep into the ground on the actual structure?
3. The design looks like it will be dark inside. But perhaps the building won't be as far underground as the drawing shows?
4. What kind of discussions have been going on regarding the "ATI" part of WOFATI? Will you spread out an "umbrella" around the structure? What about use of earth tubes and that sort of thing?
Edward, have you perused Paul's original article on wofati? If you haven't, you might get some of your concerns addressed there. I saw a video with one of Mike Oehler's houses in it--it was decades old and hadn't failed, far as I could see. Maybe if you keep the earth on the outside of the wall dry you don't get the problems you are predicting. I haven't built one of these myself, but I can't wait to see how it goes!
Jocelyn Campbell wrote:Hi Ed, I'll let others more qualified than myself answer your questions. This latest image from Tim Skufca might help clarify some things.
Ed, I agree, Oehler's design of the tongue and groove shoring seems inadequate, (for the roof decking as well). Tim Wheaton (Big Tim) and I discussed the roof decking, which will be a series of 6 to 8" diameter logs filled in with 2 to 4" diam. logs. The tips and butts will be alternated, with the small logs filling in where needed. I imagine a similar system for the wall shoring with each course pinned where possible. If a smoother wall surface is desired, I know the mill is churning out some material that could work, but, as you point out, the 10 foot span is too great of a span for 2x material. I would suggest maybe two intermediate posts to break up the span.
Paul, as far as your critique on the wing-wall design, the Sketch-up drawing doesn't show too well that there is a 5 foot overhang over the gable. This should adequately protect the front two log posts and the shoring wall. The series of vertical log posts at the end of the wing wall would basically be sacrificial logs. This is the same design that is detailed in Sepp Holzer's Permiculture book, pages 96 - 100. These posts will last several years, and are there mostly to protect the rest of that wall by supporting the overhang. The angle of these wing-walls from the main structure should relate to the site, and the amount of fill required.
Of course, this issue would not exist if the use of concrete was allowed. This brings up a question: could the use of the diesel-powered track-hoe be swapped for some key areas where it's hard to beat concrete? [remember, the Romans used grout that still is holding structures today] Just thought I'd add a little fodder to the forum.
posted 6 years ago
Jesse Biggs wrote:Here's a boat load of images we've been working with:
Your mastery of the Sketch-up program is impressive. These images are very helpful. There are a few details I'd change, though. I don't believe the double posts at the floor-level change is necessary. I know you followed Oehler's detail for the bottom purlin over the four lower posts of the 10x30 area, but if that purlin matched the others up hill from there, then the two perpendicular purlins that top the walls of the gable could share the same post for support, rather than adding another post. Doing this solves an issue I see in your sketches that has a gap at these two corners. What helps this is to put the ridge of the gable support higher up the slope (on the second purlin upslope). This also gives a steeper slope for the gable which would match the 36" in 10' (3.6"/12") slope of the other part of the building.
One last detail, the 5 foot overhang is important for protection and a knee brace is needed to accomplish this length. The ridge beam will also require a knee post, which couldn't be possible in your sketch. That is why I lowered the beam across this gable so that it could accept a knee brace.
I have a really crappy computer right now, and I am gonna return this one and get a different one. If my computer were in better condition I might try to install sketchup and have a go. But, as is, if Jesse is okay with it, I would like to see the sketchup of what is in my head. I am thinking that the slope to the ground would be shorter, the retaining wall would be smaller, and the wood in the retaining wall would be less/smaller - thus easier.
As for cement: I have a lot of goals for this structure. Including using as much material as possible from the localtrees. If we can do it with wood from the land instead of cement, I am very much in favor of that.
paul wheaton wrote: I am thinking that the slope to the ground would be shorter, the retaining wall would be smaller, and the wood in the retaining wall would be less/smaller - thus easier.
I agree, if this wing-wall were shorter, then less fill would be needed to be hauled in. However, the Sketch-up drawings do not reflect the actual site. There is hardly a slope which will require a lot of fill to cover the structure. Jesse's drawings, on the other hand, represent a site with a considerable slope, thus a need for longer wing-walls.
I would propose, if Sketch-up has the ability, to place the 0.7 WOFATI in real conditions and determine how much fill is going to be needed. This would be a good figure to give to Big Tim to determine where this material will come from.
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