[GSBN] vaulted straw bale house
bob at bobtheis.net
Tue May 19 13:22:22 CDT 2015
Having been mentioned by name, it seems appropriate to respond. Point by point:
1. is this even feasible for two full time farmers to pull off? Our schedule will only allow limited assistance. He has carpentry & a wee bit of straw bale experience and hopes to dedicate himself about half-time to building; they're both pretty sharp; there is the possibility of some work parties and farmhand help, but otherwise a limited budget for hired help. They're hoping for enclosure by winter & occupancy by next year.
As Tom points out, if you are time-constrained, don't add on the research and development of a novel construction system; use one that has a track record.
2. with mostly owner-builder work, is there any benefit to this cost-wise?
Probably not. Not to say it's terribly expensive, but you're comparing it to conventional construction, which has been optimized over decades. It IS comparatively user friendly, as the level of carpentry knowledge required is decreased ( if you eliminate conventional roof framing )
The user friendliness makes for great work parties; the bale stacking doesn't stop at the top of the wall.
Again,doubtful savings. With the armature prefabricated, the basic structure can go up quite fast. But that gets offset by the slow pace of the plastering.
3. general tips, suggestions, etc for building vaults?
A brief description of the system that's evolved through my experience:
1. Erect an internal armature of prefabricated curved ribs ( made by glueing up layers of bender board ) laid out on the bale length module.
2. Screw purlins to the outside of the ribs, centered on each bale course.
3. Stack the bales in running bond, using wood wedges ( they tuck under the strings if you lay the bales flat ) to keep each bale course tangential to the ribs.
4. After you are up three or four courses, pound light straw clay into the gaps between bales. ( You need the weight of several courses over it to get good compression. )
5. To knit the ridge together, set the bales on end and finger joint them over the ridge, pinning horizontally. Then fill the row of half bale holes down either side of the ridge.
6. Plaster the exterior of the bales, to encourage any roof leaks to run off rather than soak in. I advise pigmenting it red, so if there is a leak, you can better spot the bleeding. Secondary waterproofing - of the vapor permeable variety - to taste, over this.
7. Screw one layer of sleepers vertically down the faces, then a second layer horizontally, extending the lower ends out from the bales and adding a 2 x 4 below them to create eaves. Then screw wiggle board over that layer.
8. Corrugated sheet metal roofing actually bends to large radii in the stiff direction quite well.
9. Skylights can be made by using translucent corrugated fiberglass instead of metal, over glass plastered into gaps between bales. Fussy work, though, best avoided.
and particularly for a cold & wet climate?
All the usual disclaimers apply.
4. any comments on the their design ideas?
Since the bulk of your daylighting cones from the gable ends, don't make the vault longer than the daylight penetrates from the windows there. Use a 30˚ angle from the top of the glazing as a working measure.
They're unique and moving structures. If that's a vital element for you, go for it. Otherwise, go with what people around you know how to do.
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