Have been working thru in my head a variety of ideas on building a new home. Considerations have been: big hats and tall boots. (wide over hangs and sills that are not close to the ground.
first to build in an economic manner knowing how the price of materials are.
Second is building that will be low maintenance while long lasting.
Third simple design, with out all the crazy roof designs and rooms that just dont make a lot of sense. How many bedrooms does one need for two seniors?
Fourth is freedom from utility bills.
With all of these things in mind. I have worked thru a variety of natural materials. Some have survived my cut others have not. Each has their pro and con.
Have looked at Cob, cordwood, hempcrete, rammed earth and its variants, lime based variants along the way. Have looked at the pro and con of earthships, underground, partial underground.
What I am now seeing is that while each has wonderful things to recommend them I likely will take some positive ideas that seem to overlap. Things that are similar and that I plan to incorporate is that of high Thermal mass. That is what holds the heat and regulates temperature swings. Thick walls that are heavy. But I plan to get this mass by storing water in 2 liter bottles that are basically free and plentiful. Store them on some shelving near the ceiling. Odd idea but have seen it work and it works well.
Current building trend is towards much better control of the way we seal the building. There seem to be two big things going on here, Moisture control and air sealing. Where things get interesting in going down this path is that, the first thing that struck me and me saying OH NO, not a chance. Traditional building uses sheet materials like plywood or osb and its variants. These are used for shear wall strength. In years gone by carpenters would let in wood into the studs at angles on the corners and around doors. I had forgotten that this was the way buildings were built before the advent of these sheet goods.
As I continue my quest for how to build and what I to build with. I have learned more about insulation. I have decided to use two distinctly different materials. Cellulose it is bio degradable but mostly recycled content. No VOC No toxic chemicals to speak of. The second insulation is for use on top of the roof. Rockwool, It is basically recycled slag and pumice. It like the cellulose is it is fire proof over 1100 degrees. Both are around r3.7 - r4 / inch.
What is great about many of the other materials I have looked at is they do a great job of air sealing. Keeping the heat in or keeping it out. With air movement thru the building walls and roof you pay to keep the temperature fairly constant. As it cools you have to add heat. Many do this by burning wood. Some use mechanical means, boilers or forced air. Cooling working from the other direction. Turns out there are some excellent products being made that are both inexpensive and also do a good job allowing the movement of moisture vapor. There is always a balance that needs to be made. I look at Hemp and earth as doing this very easily. The air wont blow thru but the moisture moves thru or is retained well.
Dry walls and condensation is what I keep seeing .. Mold happens because of walls that do not dry. Condensation happens when warm wall comes in contact with cold air. Think about your glass of cold beverage in warmer air.. time to break out the coasters because of the condensation. Rotting walls is not our friend. This brings me back to two other ideas. Earth tubes that are large enough to condensate the water vapor out air in the house. Remember water runs down hill and so the tubes need to slope down and away from the house. Insulation (cosy around your coke can) is how we slow the movement of heat. Builders seem to be considering the idea of exterior insulation. It is like wrapping the house with a sweater. This to me just makes so much sense. it keeps the house from having the sheathing cold on one side and hot on the inside. This becomes the surface that is normally when condensation happens. Moisture and food for the mold to grow. The exterior insulation keeps the condensation dew point from happening.
In keeping with this idea, going back to old let in wood and no sheathing. The wall can always dry out .. Dry walls just never go away. Removing water there can be no rot happening. To keep my walls dry am looking at a nice size porch around the house. There is always something nice about a porch. It is the wide hat. Rain hits the exterior cladding. Grading and a bit more of foundation height will go a long way in keeping the bottom of the house dry. I have seen so many houses where the exterior sheathing is rotting.
Putting this together. Choosing a wall and roof structure that uses a sheeting material on the inside and outside of the frame. Think of them as super high tech tar paper. Keeps the air from moving thru but allows the wall to dry if any moisture should get in. Blow in Cellulose 12 inches in the wall. Use two stud construction. In essence it is like framing the walls twice. It keeps from needing sheathing for shear strength and the is no condensation plane.
I've been a big fan of "lots of insulation" for a long time - after all, cob homes have been built for hundreds of years and the straw in the cob is essentially that! With the advent of cheap energy, people pointed out that most of the benefit of the insulation is in the first few inches and then it drops off quickly. Also, it was being used to replace thermal mass. So we ended up with houses that need constant added heat/cooling to keep them comfy! So your thoughts of thermal mass inside and lots of insulation outside definitely resonates with me.
That said, houses built 10 to 150 years ago, managed inside water vapor by being leaky. Yes, a poor hat and boots on a house may cause the external finish to rot, but the bigger issue is to prevent it from rotting from the inside out. Cob does that by absorbing the vapor in the wet winter and drying out in the dry summer. Modern air-tight homes do that by plastic vapor barriers of limited lifespans. I don't know enough about the alternatives to figure out a better option and in our own very wet environment living in a 1970's stick-built third hand home we've broken down and are using electricity by running a dehumidifier. When we get to fixing things, controlling indoor humidity will be critical. Doing so in a long-term environmentally sound way will be equally critical.
So I encourage you to keep learning and thinking and even consider building a "small version" of some of your ideas that could eventually be a valuable office or workshop or guest cabin and see how it goes. I hope you come up with something that fits with your specific environment. More people might jump in with ideas if you post pictures of the actual spot you're thinking of building on and a bit more info on the expected weather. I always encourage people to build for the extremes - fire, flood, high winds can all be managed with forethought and most building codes are written to save lives, not save buildings. I would like permies buildings to do both!