Hybrid Walls

While we intend to build with either earthbags or cob on our homestead land in NE Georgia, we are well aware that building code enforcement may make that impossible.  As a fall-back plan, we've considered using a post- or pole-framed structure to support the roof, and using earthbags or strawbale as an infill.  Timber framing is not going to make our code inspector's hair catch on fire, and we can probably talk him into an alternative infill system much more easily than an alternative load bearing structure. 

One idea that sort of appeals to us, should we end up having to build a redundant timber frame to satisfy code, is to use BOTH bags (or cob) and strawbales to achieve both thermal mass AND insulation.  Essentially, we'd end up with a ~3 foot think wall, with earthen mass walls on the inside and strawbales on the outside (faced with earthen plaster and probably a lime coat), with the timber frame members spaced along the interface between the two wall systems.  The earthen and bale walls would be notched/shaped as needed to form up against the timbers, which would be invisible, being in the middle of the wall.  Barbed wire could be used to tie the strawbale wall to the earthen wall, and could tie both to the timbers as well, if need be. 

Has anyone tried something like this?  Anyone have thoughts on the feasibility?  Would there be undue concerns about the timbers in the middle providing an entry point into the wall structure for moisture?

Thanks,
Doug

Have you checked with the Georgia State Construction Division or whatever they may call themselves? Here in NM the Construction Industries Division, which oversees all construction, writes the rules and enforces them where cities and towns do not have their own inspectors, has had specific rules for straw bale construction for about 20 years if I'm not mistaken. Their rules are available online. As far as I know they only permit non load bearing straw bale. Not sure how earthbag fits in here; adobe bricks are permitted for new construction and have their own rule set. NM also has provision for mass wall construction as it relates to energy conservation codes.

FYI

straw  http://www.rld.state.nm.us/CID/PDFs/2008%20Codes/14%207%205%20NMAC.pdf

adobe  http://www.rld.state.nm.us/cid/GenBureau/PDFs/ProposedRules/051010/14%207%204%20NMAC-2009%20N%20M%20EARTHEN%20BUILDING%20MATERIALS%20CODE%205-10-10.pdf

energy codes  , mass wall is hidden in there someplace
http://www.rld.state.nm.us/cid/PDFs/Forms/NM%20MEC.pdf

G/L

Yes.  In GA, counties have their own building inspectors, and our particular county operates under the Southern Building Code.  The primary reason for using a timber frame is that it will be easier to get a variance for a non-load bearing infill system than it would for a structural system.

Doug

Anyone?  Anyone?  Bueller?

In particular, in such a structure, would it be feasible to build the earthen mass and/or the bale walls to a level such that they would also contribute to the support of the roof?  Would using embedded (treated) posts be a possibility?

Doug

Sounds like light clay/straw would be a perfect application for your project. It is a technique I've only recently learned about but I really like it. Its basically the middle ground between cob and straw bales, being developed by a man from New Mexico.

You take loose straw, mix it with a light clay slip made from mixing clay and water to a creamy consistancy, and pack it between your timber frame and temporary formwork. What you get after it has dried is an extremely dense wall, with both high thermal resistance, good amount of mass, and the hygroscopicity that a natural home should have.

I encourage you to check out his web site: www.econesthomes.com

We've definitely considered light clay (which was actually developed many centuries ago in Europe and is still used somewhat commonly as an infill in Germany in half-timbered buildings).  The problem we foresee with light clay, in our particular (very humid) environment, is the very lengthy drying times and the potential for mold development.  The dry season, in northeast Georgia, might not be long enough (or dry enough) to allow light clay to work. 

On that note, Patti Stouter has been doing some very interesting work recently with a hybrid of light clay and hyperadobe that she calls hyperwattle, and which looks very promising. 

Doug