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Slip Straw Clay Insulation in the Pacific Northwest

 
Maude Richards
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Location: Salish Sea
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Hello All,

I know this isn't quite Straw Bale building, but I think there is overlap in the building styles, and hopefully my questions will find their way to people with answers. We're considering building with light straw clay insulation (aka slip straw) and I am looking for ideas/help and examples of successful buildings in maritime climates of the Pacific Northwest. How does the slip straw hold up over time? What are the pitfalls to avoid? I have done a workshop and understand the process, and have been reading Econest, books from the Cob Cottage, and a book by Norbert Duerchen, but still have questions about the details of construction.

Is it better to plumb under the foundation or through the wall? Are 2x6's split in half sufficient (2x3s joined by gussets)? Does the top plate (and bottom plate for that matter) need to span to both "interior" and "exterior" walls?

I also have questions about stem walls that most resources recommend to prevent backsplash from the ground ~ what is the best way to insulate my stem wall? How high of a stem wall do I really need if I'm going to have continuous porch rooves around the perimeter of the house? Is laying a brick stem wall 12" high something I need to pay an expert to do, or can we figure it out ourselves? And how does an earthen floor interface with the rubble trench and with the stem wall?

Thank you for any help or pointers in the right direction...
 
Sean Rauch
Posts: 136
Location: Winnipeg, Manitoba
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would this be better in the cob forum?
 
allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Maude R. & the 'Permies cloud' : The primary reason to go under the foundation is to protect your plumb-ing from bad weather, which is rather what I think you mean, not
"plumb and level", Here you want things to run down hill, level is Not what you want ! A more common form of wood use within a Cob house is Large timber framing, 2nd most
common, is a wood lattice with much more use of withe's and wattle and daub, it sounds like you have been instructed on a technique that I am not familiar with, I Expect that
Jay C. White Cloud will weigh in here and straighten us out, and I will learn something new !

Actually Rafters need to span from outside wall to out side wall and rest on a Top of the wall plate or joist , The size/diameter of a piece of wood that will bridge from exterior
wall to exterior wall, we will call X, if we double the length that the joist must cross and support, the joist must be 4Xs as thick,- I think that is what you meant to ask !

With careful building starting with the french drains, and landscaping that carries all surface waters away from the house, I would insulate on the outside of the structure !

It is the length of the overhang of the eves on the roof, and how you plan on dealing with the way the water runs off of the roof that determines the safety of the cob, not
number or position of porches! The more overhang the more other things can be stored outside without failure !

Most stem walls are 30'' more or less, depending on the skill of the builder, some people do build without stem walls and go 4-5 years before applying a sedaling finish coat to
the outside walls, but that would require careful handling of the water as it flows off of the roof, and good drainage !

Earthen walls while seemingly charming and simple require a skill set that I do not have, I do not see a earthen floor in my future, I leave that for other of our fellow
members to comment on ! For the Good of the Craft !
 
Andrew Parker
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Location: Salt Lake Valley, Utah, hardiness zone 6b/7a
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"would this be better in the cob forum?"

No. Well, probably not. It really depends on how thick your slip is. For best insulation, the slip should be so thin as to be barely discernible when dried. The clay slip should be thought of as a preservative treatment and adhesive. Perhaps the best rule of thumb ought to be if you are putting straw in clay it should be discussed in the cob forum and if you are putting clay on your straw it would be appropriate to discuss it in the straw bale house forum. [note to moderator: If "bale" is taken out of the title, it would make it more inclusive.]

Just to complicate things a bit, there are methods of construction that use highly compacted (pounded, not just pushed) clay-slip covered straw that would be more appropriate to be discussed as cob or adobe.
 
Maude Richards
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Location: Salish Sea
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allen lumley wrote: Maude R. & the 'Permies cloud' : The primary reason to go under the foundation is to protect your plumb-ing from bad weather, which is rather what I think you mean, not
"plumb and level", Here you want things to run down hill, level is Not what you want ! A more common form of wood use within a Cob house is Large timber framing, 2nd most
common, is a wood lattice with much more use of withe's and wattle and daub, it sounds like you have been instructed on a technique that I am not familiar with, I Expect that
Jay C. White Cloud will weigh in here and straighten us out, and I will learn something new !

Actually Rafters need to span from outside wall to out side wall and rest on a Top of the wall plate or joist , The size/diameter of a piece of wood that will bridge from exterior
wall to exterior wall, we will call X, if we double the length that the joist must cross and support, the joist must be 4Xs as thick,- I think that is what you meant to ask !

With careful building starting with the french drains, and landscaping that carries all surface waters away from the house, I would insulate on the outside of the structure !

It is the length of the overhang of the eves on the roof, and how you plan on dealing with the way the water runs off of the roof that determines the safety of the cob, not
number or position of porches! The more overhang the more other things can be stored outside without failure !

Most stem walls are 30'' more or less, depending on the skill of the builder, some people do build without stem walls and go 4-5 years before applying a sedaling finish coat to
the outside walls, but that would require careful handling of the water as it flows off of the roof, and good drainage !

Earthen walls while seemingly charming and simple require a skill set that I do not have, I do not see a earthen floor in my future, I leave that for other of our fellow
members to comment on ! For the Good of the Craft !


Thanks for commenting, Allen. Yes, the plumbing will be sloped away from the building site, as will the rubble trench, to drain all water away. And I didn't explain the porch idea very well ~ I mean I covered porch, whose roof is connected to the main roof or comes up to the house just under the main roof, thereby extending the covered area next to the exterior wall by 4-6 feet (and hopefully negating the need for a bomber stem wall... but we'll do one anyway probably). And yes, the style we're going for is similar to wattle & daub... it's described in the book Econest, and we've seen it done locally: Larsen trusses are filled in with the clay-covered straw, and plastered over once they're dry. The Larsen trusses are two sets of 2x4 walls connected with small gussets. The total thickness is 12", and the gussets are the only "bridge" between the two walls, so thermal bridging is limited (as opposed to a "normal" 2x6 wall where the studs carry cold across the wall). Bamboo runs horizontally every 2 feet of height, resting on those gussets (it helps the straw to not settle too far). Anyway, thanks for the input! Lots to explore & learn... and perhaps I'll look around the cob forum too.

Cheers, Maude
 
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