That kind of "dragon's teeth" indicates roof insulation is *very* poor, indeed:)
Actually, there is no insulation

My grandfather didn’t spend money on insulation when he built the cabin in the 1960s. Fortunately, there is no electricity installed in the cabin, so we don’t waste energy when it’s not being used. It is only heated by burning locally sourced, self-cut firewood when it’s in use :-)