There IS insulation behind the 2x4 joists and planks. There was an extisting house here that was fallling apart, but we liked the look. To keep the look but to add the functional needs of electrical and insulation, we build a wall behind the wall you see here. In the gap we put electrical and insulation but were able to keep the look of the old structure.

What kind of corrugated roofing material is that? Did you paint that metal?