Not too long ago, when petrol was about 50 US$-cents and gas was almost free in Europe, we would “insulate” our roofs with, say 10 centimeters of mineral wool. As long as you could not look to the outside it was ok.
Not anymore. Today we have EU-requirements, translated into local regulations for each EU-country, and these requirements are very different from not-too-long-ago. At Lithouse we can easily meet these requirements, and just look at this roof. Thirty (30) centimeters of wood fiber and then on the inside another five (5) centimeters, creating a total R-value of 9.5 W/(m2⋅K).