Can I add foam board insulation to my tiny house to increase energy efficiency?

Question

I have a new tiny home shell in east Texas. It's 16x40 shell with wood siding 4x8 sheets on the out side. The kind with a groove every 4 inches. The house has a weather wrap on it already.
Metal roof. 2x4 walls and ceiling. 2x6 floor joists. 5/8 Plywood flooring. Thinking of adding 1/2" on top of that just for extra measure. Walls an floor 16" center. Ceiling 24" enter Siding is 4x8 sheets rough siding with grooves every 4"
What's the best way to insulate?
#1....Can I use 1/2" EPS foam on exterior or so I need to use a foiled foam sheet?
#2.... can I put more foam between the studs on the inside for better protection with my fiberglass insulation (Or would I need a thicker foam sheet on the inside)? I would peel the thickness of the foam off the fiberglass faced insulation.
Thanks

xeeka · Answer

Although it can' t answer the question for the best solution,
a fast and easy method for simulation is offered on the site
www.ubakus.com.
The very important parameters dew points,  moisture and drying time can be seen in seconds, thus disclosing any critical layer combination that could effect the health and damage the walls.
R value, phase shifting and more are also calculated and displayed.
Best way is to open an example and change/add layers. Each layer can be easily switched on/off to instantly see any change. Toggling  between R- value/U- value is done by clicking on the tool icon next to the result.
It is free for private use.

mreff555 · Answer

Aside from aerogels, which are outrageously expensive, the best r-value/inch that I know of is closed cell spray foam. You can get an r-value of 23 with 2x4’s.

Can I add foam board insulation to my tiny house to increase energy efficiency?

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