The key feature of any piece of appropriate architecture is that it should provide appropriate levels of thermal comfort. Providing appropriate levels of thermal comfort is complicated because it asks you to move beyond code driven, design guidelines and attempt to optimize desirable thermal comfort conditions with the costs, both internal and external, involved in achieving them. An example of this process would go something like this:

Please determine the following:

You are converting a small 1908 garage into an auxiliary dwelling unit (ADU). The garage is framed with 2×4’s studs for the walls and 2×4 rafters.

How will you achieve thermal comfort in this new shelter?
What is your thermal concept for the building?
The Oregon Residential Specialty Code calls for a minimum are R-21 insulation in the walls and R-38 in vaulted ceilings.

How will achieve this?
What kind of insulation will you use?
What is the overall thickness and make-up of your thermal envelope?
What materials will use in the construction of this wall?
Answer as a written narrative with calculations provided. I am keenly interested in the assumptions you use to generate your answer. Please be as direct as possible in explaining your assumptions.