I'm curious how folks are detailing their enclosure systems to create functional air barriers on the interior and exterior, as current best practices guidelines appear to dictate. This is, or should be, a prime concern of folks building with alternative enclosure systems because we roll-your-own types don't have the benefit of installation instructions. The goal is simple enough-- to create continuity of interior and exterior envelopes such that air is not moving into and through walls-- and thus creating all manner of moisture issues, not to mention drastic heat loss (or heat gain for you timberframers in Phoenix, AZ). But this is a pretty elusive goal too, when you consider that, by necessity, our very construction method of choice-- timberframing-- creates all manner of transitions between dissimilar materials that need to be detailed appropriately. Some folks here in the Mad River Valley of VT are doing some pretty excellent work with creating airtight strawbale enclosures. I believe the new Guild Quarterly has an article about their work and the methods they have developed-- mostly involving "airfins" at transitions between plaster and timbers. Does anybody else have anything to share about how best to approach this?
-Devin

I am thinking something along this line....

http://www.greenwallsolutions.com/

The building is built into a bank, the north side like a bank barn. It minimizes the surface area exposed to the cold and or heat. In my case the south east face would be infilled with wood chip clay using the larson truss system, over a plank wall and clay render to seal it up. As clay wood chip is more of a thermal mass system rather than an insulating R-value system it will store heat from the day, too. This is not the exterior, but has a greenhouse built around it. It would protect the wall from exposure in wetter climates and the south easterly wind driven rain, provide room for growing food year round, move the house to a zone further south, and be used for a supplement to the heating system, perhaps some duct work in the higher reaches to be blown into the house and growing beds. This duct system will keep the soil in the growing beds at 45 degrees at the coldest times in a Maine winter.

Any wall not covered with the green house would be foamed to R-50+, roof too.

My tweaking of the Earthship system, to keep it somewhere close to a traditional looking building.

I hope the people of Japan recover from the destruction. How is your Japanese?
http://www.youtube.com/watch?v=oQj7TaHc7HE

Listed in the Cons in the Guilds quarterly, one of the cons is the drying of the clay system, the green house would extend the window, thus removing it from the cons list. It will also relieve some of the pressure of the technical issues, namely the cold climate thermal mass part. I am not sure why clayless sites or regions would be exempt from using clay as a building material. Most building system are shipped from long distances. It would be nice if it was local but not totally necessary, clay is still a rather "raw" material.

So Tim, your vote is for clay render to create an air barrier on the exterior face. Moisture seems like less of a concern for a material like wood-chip clay than for other materials, like straw bale or cellulose. I'm in the process of building a double wall to be infilled with cellulose, and debating the merits/necessity of an interior air barrier. I have osb sheathing (not my favorite material, but with typar, it kept the weather out for a year and a half while I got ready for the next phase of construction), so a little bit of care in lapping and taping the roof membrane (grace tri-flex) to the typar, and the exterior face is pretty much sealed. The inside will get sawn lath over 2x2 16 o.c., and clay/lime plaster. I'm puzzling over how and whether to bother trying to get a contiguous interior envelope, similar to the "air-tight drywall approach".

I like your greenhouse idea. I have a 2 story attached greenhouse in the works on my house if and when I ever finish the basics.
-Devin

One of my concerns with the greenhouse is over heating. I am told proper venting with handle that. Automatic vent pistons, or whatever they are called, they open vents once the temp rises to a certain temperature. The smell of green plants and soil is near heaven.

Yes, a seal to keep the voids in the wood chip covered and to reduce air movement through the mix. With my plank wall I can only cover one side. But I am assuming the planks will act as the solid side or the inner side of the infill. The planks are splined as well. It is also trim, a finish look to the wall, rough wood chips just wouldn't cut it.

I keep going back and forth with the foam vs woodchip/clay wall. Foam would be the fastest, but that is not the only factor. The greenhouse would open this up to bigger and better possibilities. I would gladly swap the cost of foam for the polycarbonate sheets. Clay, wood chips, wood and time are all "free". Speaking of free, to be free from the restraints of tradition, new and old is sometimes a good feeling. I think our approach to building needs new methods and/or approaches.

I don't feel comfortable having a "vapor barrier" mixed with a clay wall system. An air barrier is a different thing, and welcome. I like the explanation of the "air fins" in the article and the rabbets on the exterior corners of the post.

I agree with tim on one thing there, a vapor barrier when dealing with a clay wall is not a good idea. The reason is that clay needs to be able to breathe and move moisture throughout itself to function properly, and I suspect with clay straw, a vapor barrier would hasten the deterioration of the wall materials.

An air barrier, however, is a must for a modern American house. Especially so if we are building for profit.

You should read up on straw clay walls in Germany, where they are typically at least 12" thick, and are both an infill and an envelope. 'Wrap and Fill' you might call it.

Another technique, which I learned from the Swiss, but the Germans use too at times, is to have a layer of tongue and grooved planking set into the timbers and plastered on both sides. Many Swiss half timbered homes actually have this in the cavities instead of masonry. This creates an effective draft barrier.

Japanese TV is so weird... I like the fiddle tune goin on in the background to let the Japanese know these folks are Americans! Think I'll go play my fiddle now...

DLB