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6 mil poly vapour barrier between framing wall and earthbag wall?

 
Posts: 20
Location: Alberta, Canada
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So I built a building. It has concreted-in posts and framed walls with lots of cross-pieces. The roof is on and complete. I have changed my mind a dozen times on how to finish the building and now I want to do a perlite/clay filled earthbag wall. I did a small earthbag project with perlite and clay and I think it would work out well. I bought a ridiculous amount of perlite and want to use it, The earthbag wall would be completely non-structural and would require some additional roof overhang.
My question is: Do I put OSB sheathing on the walls before beginning the earthbag walls? Do I put OSB on and then 6 mil poly to protect the timber framing from the earthbags? Or is that just a recipe for disaster? Do I put the earthbags right up against my 2x4 framing and put the poly on the outside of the whole wall system or do I forget the vapour barrier and just make more roof overhang?
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Add earthbag wall for insulation
 
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Hey Meagan,
Location, climate, is the building a home, 2x6/8 (looks fatty), foundation under bottom plate or is it a joist? Do you already own the osb and bags? Perlite aggregate size? clay content and aggregate composition of your clay soil?
I ask because I'd be half tempted to just stretch and staple some netting on those studs and pour the perlite loose fill, hitting from the side to settle down the loose mineral fill. But only if the conditions are right. With a good couple layers of netting (I've done it with free field fencing outside of layers of free chicken netting holding in Scoria) embedded in a quality earthen plaster it's solid. No extending eaves, no osb, no vapor barrier, no mixing your insulative perlite with thermal mass clay. Separating the perlite and clay will be better thermally. And you are already framed. Bags are flexible form work. What I suggested is formwork that is already flat for plaster. Ferrocement-ish armature (not necessarily lath), earthen plaster, mineral insulation fill that won't rot, breathable walls. "Rapidobe"-thank member 'velacreations'.
If the situation allows and it makes sense. But I've done it and like it in similar situations compared to cinder bags (pumice, Scoria, etc.)
 
Meagan Poisson
Posts: 20
Location: Alberta, Canada
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Holy Crap that is a good idea!!
Location: Alberta Canada, Climate: Fridgid (It was -30C again this morning), I built it sturdy to be an underground shelter, before I remembered that I am just a girl with hand tools and covering it in dirt was beyond my means, Yes it is meant to be liveable. The posts are dug down and concreted in, a post every 4' the horizontal 2x8 you see in the picture is only added after the posts were complete. I have lots of OSB and 5000 poly bags but I don't NEED to use them now...one never knows what might want to build in the future The Perlite (600cu ft of it) kinda does need to be used because the huge poly bags it came in are disintegrating in the sun. The Perlite pieces are about 1/8th" round. The earthbags I mixed half and half reject sand and perlite (for another project) did compress a fair bit. I have a couple truck loads of reject sand that I could use and my soil is complete clay (I could make pots out of the stuff a foot under the surface.)

Now that I look at it, I am sad that at R2.7/in, even an 8" wall of perlite will only get me an R21 wall...however, I would get no more R's if it was mixed half and half with clay 16". And filling a mesh form would be infinitely faster than bagging it. plus the not having to dig up clay...
I repeat again...Great Idea!!
I will have to research/ponder it a bit more before I have questions about it...

OMG!! - I just checked out velacreations. I think I am going to have SO MUCH FUN with this rapidobe!!
 
Meagan Poisson
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Location: Alberta, Canada
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Please forgive me if I was supposed to start a new topic rather than adding to this one, but it's on the exact same idea. I am finally ready to complete my walls. Sometime in the interim, I did put some OSB board on the outside, covering the stud wall.
I know the OSB may not have been necessary but it is on there now. I want to build a very basic outside frame, with a layer of screen and some nice rigid poly mesh to hold it while I fill the inside with my loose perlite fill. I plan to use earthen plaster, either with lath or maybe the screen and mesh would be enough....
I relish all your comments, but my only actual question is: Should I smear a layer of wet clay on the outside of the OSB to "protect" it from possible moisture wicking up through my volume of perlite. I am starting with 4-6" of gravel, and a slightly sloping ground surface so I am not sure wicking will be an issue. I have read enough of your wonderful posts (especially yours, Terry) to rethink the vapour barrier issue and I'm not planning on sticking a layer of poly anywhere, Earthen plaster inside and earthen plaster with lime finish coat for the outside...I just wonder if maybe a thin clay layer...maybe a thin clay/lime layer would be advisable on the OSB?
What do you think?
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Meagan, I think that R 2.7/inch assumes a perlite density of 3 lbs/ft3 similar to the ideal density for blown in cellulose? I always question how that is verified and how long it will sustain. I assume you would use borax as an anti-fungi and fire retardant? It will more than likely settle at the top plate, regardless an energy heel would be a good idea in your climate zone. I don't know what your code minimum is there but I'd be shooting for a r-30 wall, r-50 roof min. It gets pretty cold and wet there in Alberta correct if I am wrong. Mixing clay and perlite I'd agree with Christopher that it may not be necessary depending on the thickness, type, and content of clay plaster and it's composition moisture (MI), plastic(PI), and shrinkage(SI), indexes and PH levels. I would take to lab for testing myself but I am a perfectionist to design an accurate mix ratio. It would yeild a 4 hour burn wall I'm pretty sure higher than perlite alone with borax more like 2. What I mean primarily is depending on the material properties of the clay and perlite ratios, I'm pretty sure perlite would increase the MI property which in your wet climate may help manage water and vapor. Structurally, as an aggregate, it should improve PI an SI since it has unidirectional mechanical properties, similar to what fibers do to concrete mixes along with a planer mesh grids...that combination is unsurpassed. Clay-slip has similar properties if lab tested and executed right to prevent microbials and assure proper machine mixing. At best R 1.7/inch at a density of 13 lbs/ft3 IIRC....Most hand mixes are getting around R.6-.8 at best

Bear in mind it is not all about r-value, surface layer clay mass effect can take an r-21 perlite core wall with no settling issues and make it perform 30+. So IF you do achieve R21 and you can verify that by density, add a couple inches of clay plaster on anything but metal due to it's corrosion and oxide jacking issues, it should be good on the walls crack free. Regardless of what method 90% of issues on walls are due to insufficient overhangs, eave extensions, ground slopes. In your wet climate add some out-riggers to get at least 24" if need be.

Another large consideration is brace wall (shear, racking) requirements.....that resist seismic and wind lateral loads. Look at IRC 2012 table 602.10.4 bracing methods, page 173 , Method three CS or CS-WSP( continuous sheathed-wood structural panel, (or CAN Spec) see video: https://www.youtube.com/watch?v=xTXVBxIIG5g If you continuous sheath with properly rated OSB you should be ok but, you may have higher requirements due to wind and seismic like frame-to foundation hold downs at door and window wall openings, or post. The min. nail schedule is 8D, 6 OC edges, 12 field, 1.5" penetration on 3/8 OSB but can be higher if the wall-to-eave height is greater than 10', wall dead load greater than 20 PSF, floor greater than 10 PSF, SDC "C" and above. BTW stud blocking and chicken wire is not an approved structural wall brace. Let in simpson metal or wood straps are or 3/4 wood diagonal lath panels are. If you want your own design method hire a PE.

The stone should do a decent job as a capillary break....Capillary uptake/suction is the most mysterious action and difficult to quantify......materials such as clay/lime/MGO rock aggregate ground renders that have high composite hygroscopic properties have been proven to stop it dead in it's tracks, no plastic since it is a microbial source and does not sustain especially at 6 mil....now they are going to 20+ might as well make a 1/4 HDPE

OSB: Poly/most house wraps, against OSB is a microbial disaster. I'd agree due to it's surface issues an inert isolation layer of clay or lime render cannot hurt although you void the warranty by altering the materials if you care. I use a mineral mix MGO or lime, borax, filtered clay and water mix and pump spray all my wood to help anti-fungi/ petrify it, or mineral paint...In my opinion, that help stabilize any microbial reactions with other materials and provides a protective coating from the elements. Again, please understand those properties would take some lab testing for starters so take my opinion with a grain of salt. Air seal all penetrations.

If you can get that perlite core in and from settling @ 3lbs.ft3 (or whatever design allowable it has) that should do good at preventing moist convective air cavity loops from degrading r-values, enhance air sealing along with the clay renders that only improve with higher heat and moisture gradients if there are no plastic barriers to inhibit performance and allow access to the perlite core or aggregates .
 
Meagan Poisson
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Location: Alberta, Canada
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Thankyou Terry,
I enjoy your responses. They take about six readings for me to understand what you say (your vast knowledge is hard for me to grasp) but I think I got it
 
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