Comments on: The Ideal Wall http://rusticprecision.com/blog/2008/04/17/the-ideal-wall/ Wed, 23 Apr 2008 22:47:51 +0000 http://wordpress.org/?v=2.8.4 hourly 1 By: Chris http://rusticprecision.com/blog/2008/04/17/the-ideal-wall/comment-page-1/#comment-11 Chris Wed, 23 Apr 2008 22:47:51 +0000 http://rusticprecision.com/blog/2008/04/17/the-ideal-wall/#comment-11 Hi Stephen, I like your idea, and I think it should work well. I don't think condensation between the bales and CEB should be an issue. Just the same, I'd try to make the whole wall an unvented assembly by intentionally leaving a gap between the CEB wall and the bales, and filling this gap completely with adobe mortar. Depending on the consistency of your mortar, you'll need a gap of at least 1", and maybe 2", to be able to work the mortar all the way to the bottom. Be sure to do the mortaring with each bale course, as you won't be able to work the stuff down in there after the fact. <br/>With the mortar, CEB wall, and interior plaster, what you will have created is a very thick, earthen, breathable interior "plaster". I would guess that the CEBs will have lower permeability than the mortar or your interior finish plaster, but they should still breathe. With this design, the straw bales should be able to vent vapor in both directions. <br/>I recommend a lime- or earth-based exterior plaster/stucco. There are plenty of papered, wired and cement stuccoed bales houses around, but, personally, they make me nervous. Any water that gets trapped inside a bale wall creates compost. This is because cement stucco has a propensity to crack and let water in, but is less generous about letting it out again. I guess the message is, if you go the cement stucco route, make sure your drainage plane works: the stucco paper is water tight; a small air gap exists between it and the stucco; and the weepscreed at the bottom lets water out. That's pretty standard for stucco these days. <br/> I assume you will be attaching windows to bucks frame into the CEB part of the wall? If so, make sure to "pan" the window sills all the way out to the exterior edge of the bale wall and beyond (or lip it over the stucco paper/drainage plane if you go the cement stucco route). The pan should have positive slope. To accomplish this, you can either cut a bevel in your lower window sill, or add a beveled furring strip. To install the window without piercing the pan, cut or otherwise remove the portions of the nailing fins that get in the way (i.e, the bottom fin and a portion of the sides) and nail the fins everywhere else. Use spray foam generously for extra anchorage all the way around the window. <br/>You can make custom-sized soft window pans by making a sandwich of bituthene, synthetic roof underlayment (e.g, "Titanium"), and self-furring plaster lath. Landscape staples (heavy-gauge wire U-shaped staples) and Sikaflex adhesive may help. Roofing supply stores sell bituthene in 30" or 36" wide rolls (about $170 ea, last I checked.) The stuff is tacky on one side. Apply the roof underlayment to the tacky side to protect the bituthene from UV light destruction. After you put those two components together and create a pan with a U-shaped cross-section (lapped up at least 2" on either side), bend a piece of plaster lath so that it extends from the outside of the wooden window buck to beyond the edge of bale. Attach the lath to the bales with the landscape staples, and to the bituthene/underlayment with the Sikaflex. Don't pierce your pan with anything. The first two layers of your pan are for waterproofing, the lath is so that the plaster will stick to it. <br/>If you do cast-in-place concrete window sills (and if you do, don't forget to stop the bales short of the window buck to allow sufficient depth!), your sill will cover most of the pan. However, the lath will come in handy when it comes time to plaster the sides of the pan above the sill. <br/>If all goes well, this wall assembly should last a very, very long time. Make sure you put an adequate concrete foundation under it, with adequate reinforcing steel. Also, it's best to get drainage under the first course of bales. One way to do this is to cast a step up for your CEB area that extends 4" into the bale area. Slope the rest out to the exterior edge. Now cast a small curb, with drain slots every 12-24", on the outside to bring the outside edge level with the other side of the foundation. Now you have a drained "moat" underneath most of the bale that you can then fill with pea gravel. As an alternative to casting that outer curb, you can anchor bolt a perimeter of pressure treated (or heart redwood) 4x4 there instead. Notch your drainage slots on the bottom first with a skilsaw. <br/>If not all this makes sense, I might be able to draw some pictures. <br/>Feel free to ask more questions, and keep me updated with respect to your progress. <br/>Cheers, Chris Hi Stephen,
I like your idea, and I think it should work well. I don’t think condensation between the bales and CEB should be an issue. Just the same, I’d try to make the whole wall an unvented assembly by intentionally leaving a gap between the CEB wall and the bales, and filling this gap completely with adobe mortar. Depending on the consistency of your mortar, you’ll need a gap of at least 1″, and maybe 2″, to be able to work the mortar all the way to the bottom. Be sure to do the mortaring with each bale course, as you won’t be able to work the stuff down in there after the fact.

With the mortar, CEB wall, and interior plaster, what you will have created is a very thick, earthen, breathable interior “plaster”. I would guess that the CEBs will have lower permeability than the mortar or your interior finish plaster, but they should still breathe. With this design, the straw bales should be able to vent vapor in both directions.

I recommend a lime- or earth-based exterior plaster/stucco. There are plenty of papered, wired and cement stuccoed bales houses around, but, personally, they make me nervous. Any water that gets trapped inside a bale wall creates compost. This is because cement stucco has a propensity to crack and let water in, but is less generous about letting it out again. I guess the message is, if you go the cement stucco route, make sure your drainage plane works: the stucco paper is water tight; a small air gap exists between it and the stucco; and the weepscreed at the bottom lets water out. That’s pretty standard for stucco these days.

I assume you will be attaching windows to bucks frame into the CEB part of the wall? If so, make sure to “pan” the window sills all the way out to the exterior edge of the bale wall and beyond (or lip it over the stucco paper/drainage plane if you go the cement stucco route). The pan should have positive slope. To accomplish this, you can either cut a bevel in your lower window sill, or add a beveled furring strip. To install the window without piercing the pan, cut or otherwise remove the portions of the nailing fins that get in the way (i.e, the bottom fin and a portion of the sides) and nail the fins everywhere else. Use spray foam generously for extra anchorage all the way around the window.

You can make custom-sized soft window pans by making a sandwich of bituthene, synthetic roof underlayment (e.g, “Titanium”), and self-furring plaster lath. Landscape staples (heavy-gauge wire U-shaped staples) and Sikaflex adhesive may help. Roofing supply stores sell bituthene in 30″ or 36″ wide rolls (about $170 ea, last I checked.) The stuff is tacky on one side. Apply the roof underlayment to the tacky side to protect the bituthene from UV light destruction. After you put those two components together and create a pan with a U-shaped cross-section (lapped up at least 2″ on either side), bend a piece of plaster lath so that it extends from the outside of the wooden window buck to beyond the edge of bale. Attach the lath to the bales with the landscape staples, and to the bituthene/underlayment with the Sikaflex. Don’t pierce your pan with anything. The first two layers of your pan are for waterproofing, the lath is so that the plaster will stick to it.

If you do cast-in-place concrete window sills (and if you do, don’t forget to stop the bales short of the window buck to allow sufficient depth!), your sill will cover most of the pan. However, the lath will come in handy when it comes time to plaster the sides of the pan above the sill.

If all goes well, this wall assembly should last a very, very long time. Make sure you put an adequate concrete foundation under it, with adequate reinforcing steel. Also, it’s best to get drainage under the first course of bales. One way to do this is to cast a step up for your CEB area that extends 4″ into the bale area. Slope the rest out to the exterior edge. Now cast a small curb, with drain slots every 12-24″, on the outside to bring the outside edge level with the other side of the foundation. Now you have a drained “moat” underneath most of the bale that you can then fill with pea gravel. As an alternative to casting that outer curb, you can anchor bolt a perimeter of pressure treated (or heart redwood) 4×4 there instead. Notch your drainage slots on the bottom first with a skilsaw.

If not all this makes sense, I might be able to draw some pictures.

Feel free to ask more questions, and keep me updated with respect to your progress.

Cheers,
Chris

]]> By: Stephen http://rusticprecision.com/blog/2008/04/17/the-ideal-wall/comment-page-1/#comment-10 Stephen Wed, 23 Apr 2008 22:44:26 +0000 http://rusticprecision.com/blog/2008/04/17/the-ideal-wall/#comment-10 Dear Mr. Schille I came across your article on The Ideal Wall. I am currently looking at building a passive solar compressed earth block (CEB) home in Midland, Texas. In googling the internet, I cannot find any real discussion on a wall concept using CEB for the interior load bearing walls (on the outside perimeter) with straw bale located on the outside of the CEB for insulation. Is this a reasonable concept or will the back of the bale abutting the CEB become a condensation/mold issue (both the front of the straw bale (to the environment) and the inside of the CEB perimeter wall will be plastered). The Midland climate is a desert climate with normally low humidity levels. Any thoughts/guidance would be greatly appreciated. Sincerely, Stephen Dear Mr. Schille
I came across your article on The Ideal Wall. I am currently looking at building a passive solar compressed earth block (CEB) home in Midland, Texas. In googling the internet, I cannot find any real discussion on a wall concept using CEB for the interior load bearing walls (on the outside perimeter) with straw bale located on the outside of the CEB for insulation. Is this a reasonable concept or will the back of the bale abutting the CEB become a condensation/mold issue (both the front of the straw bale (to the environment) and the inside of the CEB perimeter wall will be plastered). The Midland climate is a desert climate with normally low humidity levels.
Any thoughts/guidance would be greatly appreciated.

Sincerely,
Stephen

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