Flexible System for Small Farm Buildings

Hi all. I'm trying to plan a cheap, flexible system that I can use for making a number of small buildings that range in function from coops and sheds to workshops and living spaces. I'm in Tennessee, zone 7a, so it's hot, humid summers and winters that are fairly mild most of the season, with a few weeks of serious cold and a little bit of snow. I have a few requirements that make it a bit more complicated than usual, but also some things I don't need which should make it easier.

Requirements:
Cheap (very cheap).
Buildable in stages (ie don't have to fork out for all the materials at once).
No materials that are even a little bit toxic (my landlord is pretty strict about this, so no formaldehydes, no PVC etc etc, basically 'natural' materials only).
Buildable on pier foundations and movable by trailer (not frequently, but eventually).   I can do some disassembly for this, but I'm hoping to keep it quite light, so no heavy mass cob walls or anything.
Termite resistant.
Breathable. This is a mixed climate where water vapor will be moving from exterior to interior some of the time, and the reverse some of the time.

Preferred qualities:
A system where I can put up framing, siding and roof first to keep the rain out, then seal and insulate from the inside (both to make the build process smoother and to allow changes in building function over time).
Modifiable for different uses. Particularly the ability to add increasing layers of insulation from the inside if needed, and to install windows after the fact.
Simple, using few materials. Preferably walls, floor and ceiling use same/similar methods.
Forgiving of bad carpentry and rough-cut wood, wood in various states of dryness, and changing uses. So nothing where the exact matching of vapor retarders to heating systems is critical, nothing where a few drops of errant water will lead to mould everywhere, and nothing modular that relies on every piece of wood being perfectly straight and exactly the same thickness.
Buildable in any season, so no systems that need three months of  sunny weather to dry.
Aesthetically pleasing and human-friendly (at least in a simple, rustic way).

Factors that make it easier:
I'm building very small. Everything will be 8' wide or less, single story (probably without lofts), and between 12' and 16' long. I'll expand with multiple small buildings (or wings) rather than any really big ones.
Codes are not an issue for me here because of small size and agricultural use.
Perfect climate control is not the aim. Some of these units will be totally uninsulated sheds, some will be workshops that I only use in the daytime, and one will be a living space, but none of them need to be built to passive house standards. I've already lived a year here in an unsinulated, leaky barn here and it's totally do-able, so any insulation, thermal mass and airtightness are a bonus. Basically it should be heatable in winter and tolerable in summer with a  window open and a fan running.
Farm standards, not magazine standards. Basically these little buildings will have long-term function as farm sheds of various sorts, but they'll probably only be used as living space and workshop space for two to three years. I'm youngish, single and accustomed to rough standards of living, so nothing has to be finished up in a fancy way, and there's no high-paying client to please. That said, they have to look vaguely nice, so no shanty-town style assemblies of free scrap materials that don't match.
No need to run utilities inside the walls.

Easily available materials:
Cheapish locally milled wood, including lots of Eastern Red Cedar.
Free and cheap metal roofing from old barns.
Free wood scraps of various shapes and sizes.
Free sawdust.
High-clay soils.
Hay.
The usual hardware store stuff.

Unavailable materials:
Straw (it would have to be organic to meet landlord's requirements, and there's none of that around here).

Given the materials and (low) skills I have available, I'm trying to work out a system along these lines: simple wood framing or post and beam for load-bearing structure (with enough bracing to handle shear loads). Board and batten cedar siding on the exterior, metal roof.  Some kind of insulative clay infill between framing members.

My thinking is that board and batten is easy to do and very forgiving of wood shrinkage (it also fits in well with surrounding buildings here). Because of the horizontal strip required for nailing into, it also can be made with a good air gap between siding and the framing, so that should help with allowing the clay infill to dry even if it's put in after the siding (the horizontal strips in this case may actually be 1" boards placed diagonally to take care of shear forces).

For the infill, I'm thinking either wood chip light clay or biochar clay plaster (like this: https://www.biochar-journal.org/en/ct/3). To allow for the application of the infill without closing the air gap between wall and siding, I would put lath strips (or wire mesh?) between framing members as an armature for the clay infill to key into. I have access to free wood scraps that could serve as lath in this context. I'm not planning to go for really thick walls with fantastic R-value, just a few inches to moderate the interior climate (probably 1" to 4" depending on intended use). Again, it's a fairly mild climate here and I'm not looking for perfection.

I've attached some little drawings to show what I mean about the walls. Before I go into all the details of how to do the ceiling and floor etc, I'm wondering if you all think that would work as an approach for the walls.  Will a 1" to 1.5" air gap between wall and siding allow an insulative clay infill to dry out? I think wood chip light clay would be a nice, relatively low-labor solution here, but as I understand it, drying can be an issue. If that is the case, the biochar plaster (more labor intensive but probably a better insulator) might still work as it can be applied to the armature in thin layers that have time to dry.

If this approach will work as a construction method, would the clay infill have to be "exterior grade" (ie mixed with lime) because some moisture will occasionally make its way through the siding, or could a simple clay mix handle the occasional drop of water as long as it can dry out?

And just to be clear about what I mean by the various different uses and building the siding first: the idea is that I can start by building for example an 8'x12' board and batten shed, then afterwards modify it from within with a bit of insulative clay infill to serve as a poultry brooding house, a bit more to serve as a workshop, or a lot more to serve as a tiny living space. Each little building can then change uses over time if need be by adding more infill, putting in or taking out windows, etc.

I plan to do some little trials to see if this will work, but would welcome any thoughts and suggestions before I put any time or money into it.   Don't be afraid to tell me if this is totally stupid, I'd rather find out now. Thanks in advance for your help!

What is  your advantage that will allow you build cheap? Or cheaper than the next guy? Ever consider working for a local company building garages just to learn the rules of their existence? Unless you've already worked with a good construction crew, there's a lot to be learned - just about everything, in fact. A bit of practical local knowledge often weighs heavier than any number of careful theories. Of course, most businesses won't be doing a "clean" build - but they will be dealing with the location and culture you are in and can demonstrate the endless adaptation it takes to get something done and built. And that's doing it the easy way, just like everybody else. Throw in new untested theories, skills, etc and life gets way more interesting.



Rufus

With 'Cheap" do you mean poor quality?

There are a lot of things that can be done very inexpensively without sacrificing functional quality. A low level of finish is prime among those; if it doesn't need to look fancy it can often be done by semiskilled labor, learning with practice. Developing a single modular-type method would be very helpful here, as early efforts which may have major flaws can be used for minor functions like storage sheds, leading to good construction quality in structures used for living space.

I think the rain screen board & batten would work fine as an initial layer, and with an inch of air space and a relatively thin light cobbish insulating layer should not present problems in drying. Timber frame structures with wattle and daub infill all exposed to the elements have been built for centuries in Europe, and with appropriate detailing can be durable.